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SCIENTIFIC AMERICAN SUPPLEMENT NO. 821

NEW YORK, September 26, 1891

Scientific American Supplement. Vol. XXXII, No. 821.

Scientific American established 1845

Scientific American Supplement, $5 a year.

Scientific American and Supplement, $7 a year.

TABLE OF CONTENTS.

I.    Architectural.--The New Labor Exchange in Paris.--With
      views of the interior and exterior of the building

II.   Electrical.--The Construction and Maintenance of Underground
      Circuits.--By S.B. FOWLER.--A comprehensive article,
      discussing at length the various devices for protecting underground
      circuits, methods _of_ inserting the cables, etc.

III.  Engineering.--Railroads to the Clouds.--Sketches of a number
      of mountain railroads

IV.   Marine Engineering.--The French Armored Turret Ship
      the Marceau.--1 engraving.--A full description of the vessel, giving
      dimensions and cost

      A Review of Marine Engineering during the Past Decade.--A
      paper read before the Institution of Mechanical Engineers by Mr.
      Alfred Blechynben, of Barrow-in-Furness.--This paper, which
      is continued from Supplement No. 820, treats on steam pipes,
      feed water heating, twin screws, etc.

V.    Miscellaneous.--The Little House.--An article giving various
      hints about the arrangement and management of small
      dwellings, with special view to the best sanitary arrangements

      Stilt Walking.--A sketch, with engraving, of Sylvain Dornon,
      the stilt walker of Landes

      Remains of a Roman Villa in England

      Gum Arabic and its Modern Substitutes.--A continuation of a
      paper by Dr. S. Rideal and W.E. Youle.--With 26 tables

      A New Method of Extinguishing Fires.--Invented by George
      Dickson and David A. Jones, of Toronto, Canada.--Apparatus designed
      to utilize a mixture of water and liquefied carbonic acid

VI.   Medicine and Hygiene.--The Hygienic Treatment of
      Obesity.--By Dr. Paul Chebon.--Methods of eating, drinking,
      and exercising for the purpose of reducing fat.--An extended
      article, giving valuable information to people troubled with too
      much flesh

VII.  Photography.--Spectroscopic Determination of the Sensitiveness
      of Dry Plates.--A full description of the new plan of
      Mr. G.F. WILLIAMS, for determining the sensitiveness of dry
      plates by the use of a small direct vision pocket spectroscope

VIII. Physics.--A Physical Laboratory Indicator.--By J.W.
      MOORE, of Lafayette College.--1 engraving.--This is a modification
      of the old peg board adapted to use in the laboratory.--It indicates
      the names of the members of the class, contains a full
      list of the experiments to be performed, refers the student
      to the book and page where information in reference to experiments
      or apparatus may be found, it shows what experiments
      are to be performed by each student at a given time, etc.

      Cailletet's Cryogen.--A description, with one engraving, of Mr.
      Cailletet's new apparatus for producing temperatures from 70
      degrees to 80 degrees C., below zero, through the expansion of
      liquid carbonic acid

IX.   Technology.--The Manufacture of Roll Tar Paper.--An extended
      article containing a historical sketch and full information
      as to the materials used and the methods of manufacture

      Smokeless Gunpowder.--By Hudson Maxim.--A comprehensive
      article on the manufacture and use of smokeless gunpowder,
      giving a sketch of its history, and describing the methods of
      manufacture and its characteristics

      Method of Producing Alcohol.--A description of an improved
      process for making alcohol.--Invented by Mr. Alfred Springer,
      of Cincinnati, Ohio

[Illustration: INTERIOR OF THE NEW LABOR EXCHANGE, PARIS.]

[Illustration: NEW LABOR EXCHANGE, PARIS.]

THE NEW LABOR EXCHANGE, PARIS.

The new Labor Exchange is soon to be inaugurated. We give herewith a
view of the entrance facade of the meeting hall. The buildings, which
are the work of Mr Bouvard, architect, of the city of Paris, are
comprised within the block of houses whose sharp angle forms upon
Place de la Republique, the intersection of Boulevard Magenta and
Bondy street. One of the entrances of the Exchange is on a level with
this street. The three others are on Chateau d'Eau street, where the
facade of the edifice extends for a length of one hundred feet. From
the facade and above the balcony that projects from the first story,
stand out in bold relief three heads surrounded by foliage and fruit
that dominate the three entrance doors. These sculptures represent the
Republic between Labor and Peace. The windows of the upper stories are
set within nine rows of columns, from between the capitals of which
stand out the names of the manufacturers, inventors, and statesmen
that have sprung from the laboring classes. Upon the same line, at the
two extremities of the facade, two modillions, traversed through their
center by palms, bear the devices "Labor" and "Peace." Above, there is
a dial surmounted by a shield bearing the device of the city of Paris.

The central door of the ground floor opens upon a large vestibule,
around which are arranged symmetrically the post, telegraph,
telephone, and intelligence offices, etc. Beyond the vestibule there
is a gallery that leads to the central court, upon the site of which
has been erected the grand assembly hall. This latter, which measures
20 meters in length, 22 in width, and 6 in height, is lighted by a
glazed ceiling, and contains ten rows of benches. These latter contain
900 seats, arranged in the form of circular steps, radiating around
the president's platform, which is one meter in height. A special
combination will permit of increasing the number of seats reserved for
the labor associations on occasions of grand reunions to 1,200. The
oak doors forming the lateral bays of the hall will open upon the two
large assembly rooms and the three waiting rooms constructed around
the faces of the large hall. In the assembly rooms forming one with
the central hall will take place the deliberations of the syndic
chambers. The walls of the hall will, ere long, receive decorative
paintings.--_L'Illustration._

MANUFACTURE OF ROLL TAR PAPER.

Roofing paper was first used in Scandinavia early as the last century,
the invention being accredited to Faxa, an official of the Swedish
Admiralty. The first tar and gravel roofs in Sweden were very
defective. The impregnation of the paper with a water-proofing liquid
had not been thought of, and the roofs were constructed by laying over
the rafters a boarding, upon which the unsaturated paper, the sides of
which lapped over the other, was fastened with short tacks. The
surface of the paper was next coated with heated pine tar to make it
waterproof. The thin layer of tar was soon destroyed by the weather,
so that the paper, swelled by the absorption of rain water, lost its
cohesiveness and was soon destroyed by the elements. This imperfect
method of roof covering found no great favor and was but seldom
employed.

In Germany the architect Gilly was first to become interested in tar
paper roofing, and recommended it in his architecture for the country.
Nevertheless the new style of roof covering was but little employed,
and was finally abandoned during the first year of the 19th century.
It was revived again in 1840, when people began to take a renewed
interest in tar paper roofs, the method of manufacturing an
impermeable paper being already so far perfected that the squares of
paper were dipped in tar until thoroughly saturated. The roof
constructed of these waterproof paper sheets proved itself to be a
durable covering, being unimpenetrable to atmospheric precipitations,
and soon several factories commenced manufacturing the paper. The
product was improved continually and its method of manufacture
perfected. The good qualities of tar paper roofs being recognized by
the public, they were gradually adopted. The costly pine tar was soon
replaced by the cheaper coal tar. Square sheets of paper were made at
first; they were dipped sufficiently long in ordinary heated coal tar,
until perfectly saturated. The excess of tar was then permitted to
drip off, and the sheets were dried in the air. The improvement of
passing them through rollers to get rid of the surplus tar was
reserved for a future time, when an enterprising manufacturer
commenced to make endless tar paper in place of sheets. Special
apparatus were constructed to impregnate these rolls with tar; they
were imperfect at first, but gradually improved to a high degree. Much
progress was also made in the construction of the roofs, and several
methods of covering were devised. The defects caused by the old method
of nailing the tar paper direct upon the roof boarding were corrected;
the consequence of this method was that the paper was apt to tear,
caused by the unequal expansion of the roofing boards and paper, and
this soon led to the idea of making the latter independent of the
former by nailing the sides of the paper upon strips running parallel
with the gable. The use of endless tar paper proved to be an essential
advantage, because the number of seams as well as places where it had
to be nailed to the roof boarding was largely decreased. The
manufacture of tar paper has remained at about the same stage and no
essential improvements have been made up to the present. As partial
improvement may be mentioned the preparation of tar, especially since
the introduction of the tar distillery, and the manufacture of special
roof lacquers, which have been used for coating in place of the coal
tar. As an essential progress in the tar paper roofing may be
mentioned the invention of the double tar paper roof, and the wood
cement roof, which is regarded as an offshoot.

The tar paper industry has, within the last forty years, assumed great
dimensions, and the preferences for this roofing are gaining ground
daily. In view of the small weight of the covering material, the wood
construction of the roof can be much lighter, and the building is
therefore less strained by the weight of the roof than one with the
other kind, so that the outer walls need not be as heavy. Considering
the price, the paper roof is not only cheaper than other fireproof
roofs, but its light weight makes it possible for the whole building
to be constructed lighter and cheaper. The durability of the tar paper
roof is satisfactory, if carefully made of good material; the double
tar paper roof, the gravel double roof, and the wood cement roof are
distinguished by their great durability.

These roofs may be used for all kinds of buildings, and not only are
factories, storehouses, and country buildings covered with it, but
also many dwellings. The most stylish residences and villas are at
present being inclosed with the more durable kinds; the double roof,
the gravel double roof, and the wood cement roof. For factory
buildings, which are constantly shaken by the vibrations of the
machinery, the tar paper roof is preferable to any other.

In order to ascertain to what degree tar paper roofs would resist
fire, experiments were instituted at the instigation of some of the
larger manufacturers of roofing paper, in the presence of experts,
architects, and others, embracing the most severe tests, and it was
fully proved that the tar paper roof is as fireproof as any other.
These experiments were made in two different ways; first, the
readiness of ignition of the tar paper roof by a spark or flame from
the outside was considered, and, second, it was tested in how far it
would resist a fire in the interior of the building. In the former
case, it was ascertained that a bright, intense fire could be kept
burning upon the roof for some time, without igniting the woodwork of
the roof, but heat from above caused some of the more volatile
constituents of the tar to be expelled, whereby small flames appeared
upon the surface within the limits of the fire; the roofing paper was
not completely destroyed. There always remained a cohesive substance,
although it was charred and friable, which by reason of its bad
conductivity of heat protected the roof boarding to such an extent
that it was "browned" only by the developed tar vapors. A fire was
next started within a building covered with a tar paper roof; the
flame touched the roof boarding, which partly commenced to char and
smoulder, but the bright burning of the wood was prevented by the
air-tight condition of the roof; the fire gases could not escape from
the building. The smoke collecting under the roof prevented the
entrance of fresh air, in consequence of which the want of oxygen
smothered the fire. The roofing paper remained unchanged. By making
openings in the sides of the building so that the fire gases could
escape, the wood part of the roof was consumed, but the roofing paper
itself was only charred and did not burn. After removing the fire in
contact with the paper, this ceased burning at once and evinced no
disposition whatever to spread. In large conflagrations, also, the tar
paper roofs behaved in identically a similar manner. Many instances
have occurred where the tar paper roof prevented the fire from
spreading inside the building, and developing with sufficient
intensity to work injury.

As it is of interest to the roofer to know the manner of making the
material he uses, we give in the following a short description of the
manufacture of roofing paper. At first, when square sheets were used
exclusively, the raw paper consisted of ordinary dipped or formed
sheets. The materials used in its manufacture were common woolen rags
and other material. In order to prepare the pulp from the rags it is
necessary to cut them so small that the fabric is entirely dissolved
and converted into short fibers. The rags are for this purpose first
cut into pieces, which are again reduced by special machines. The rags
are cut in a rag cutting machine, which was formerly constructed
similar to a feed cutter; later on, more complicated machines of
various constructions were employed. It is not our task to describe
the various kinds, but we remain content with the general remark that
they are all based on the principles of causing revolving knives to
operate upon the rags. The careful cleansing of the cut rags,
necessary for the manufacture of paper, is not required for roofing
paper. It is sufficient to rinse away the sand and other solid
extraneous matter. The further reduction of the cut rags was formerly
performed in a stamp mill, which is no longer employed, the pulp mill
or rag engine being universally used.

The construction of this engine may be described as follows: A box or
trough of wood, iron, or stone is by a partition divided into two
parts which are connected at their ends. At one side upon the bottom
of the box lies an oakwood block, called the back fall. In a hollow of
this back fall is sunk the so-called plate, furnished with a number of
sharp steel cutters or knives, lying alongside of each other. A roller
of solid oakwood, the circumference of which is also furnished with
sharp steel cutters or knives, is fastened upon a shaft and revolves
within the hollow. The journal bearings of the shaft are let into and
fastened in movable wooden carriers. The carriers of the bearings may
be raised and lowered by turning suitable thumbscrews, whereby the
distance between the roller and the back fall is increased or
decreased. The whole is above covered with a dome, the so-called case,
to prevent the throwing out of the mass under the operation of
grinding. The roller is revolved with a velocity of from 100 to 150
revolutions per minute, whereby the rags are sucked in between the
roller and the back fall and cut and torn between the knives. At the
beginning of the operation, the distance between the roller and the
back fall is made as great as possible, the intention being less to
cut the rags than to wash them thoroughly. The dirty water is then
drawn off and replaced by clean, and the space of the grinding
apparatus is lessened gradually, so as to cut the rags between the
knives. The mass is constantly kept in motion and each piece of rag
passes repeatedly between the knives. The case protects the mass from
being thrown out by the centrifugal force. The work of beating the
rags is ended in a few hours, and the ensuing thin paste is drawn off
into the pulp chest, this being a square box lined with lead.

From the pulp chest it passes to the form of the paper machine. This
form consists of an endless fine web of brass wire, which revolves
around rollers. The upper part of this form rests upon a number of
hollow copper rollers, whereby a level place is formed. The form
revolves uniformly around the two end rollers, and has at the same
time a vibratory motion, by which the pulp running upon the form is
spread out uniformly and conducted along, more flowing on as the
latter progresses. The water escapes rapidly through the close wire
web. In order to limit the form on the sides two endless leather
straps revolve around the rollers on each side, which touch with their
lower parts the form on both sides and confine the fluid within a
proper breadth. The thickness of the pulp is regulated at the head of
the form by a brass rule standing at a certain height; its function is
to level the pulp and distribute it at a certain thickness. The
continually moving pulp layer assumes greater consistency the nearer
it approaches to the dandy roll. This is a cylinder covered with brass
wire, and is for the purpose of compressing the paper, after it has
left the form, and free it from a great part of the water, which
escapes into a box. The paper is now freed of a good deal of the
fluid, and assumes a consistency with which it is enabled to leave the
form, which now commences to return underneath the paper, passing on
to an endless felt, which revolves around rollers and delivers it to
two iron rolls. The paper passes through a second pair of iron
rollers, the interiors of which are heated by steam. These rollers
cause the last of the water to be evaporated, so that it can then be
rolled upon reels. A special arrangement shaves the edges to the exact
size required.

The paper is made in different thicknesses and designated by numbers
to the size and weight.

Waste paper, bookbinders' shavings, etc., can be used for making the
paper. As much wool as possible should be employed, because the wool
fiber has a greater resistance than vegetable fiber to the effects of
the temperature. By wool fiber is understood the horny substance
resembling hair, with the difference that the former has no marrowy
tissue. The covering pellicle of the wool fiber consists of flat,
mostly elongated leaves, with more or less corners, lying over each
other like scales, which makes the surface of the fiber rough; this
condition, together with the inclination of curling, renders it
capable of felting readily. Pure wool consists of a horny substance,
containing both nitrogen and sulphur, and dissolves in a potash
solution. In a clean condition, the wool contains from 0.3 to 0.5 per
cent. of ash. It is very hygroscopical, and under ordinary
circumstances it contains from 13 to 16 per cent. humidity, in dry air
from 7 to 11 per cent., which can be entirely expelled at a
temperature of from 226 to 230 degrees Fahrenheit. Wool when ignited
does not burn with a bright flame, as vegetable fiber does, but
consumes with a feeble smouldering glow, soon extinguishes, spreading
a disagreeable pungent vapor, as of burning horn. By placing a test
tube with a solution of five parts caustic potash in 100 parts water,
a mixture of vegetable fibers and wool fibers, the latter dissolve if
the fluid is brought to boiling above an alcohol flame, while the
cotton and linen fibers remain intact.

The solubility of the woolen fibers in potash lye is a ready means of
ascertaining the percentage of wool fiber in the paper. An exhaustive
analysis of the latter can be performed in the following manner: A
known quantity of the paper is slowly dried in a drying apparatus at
temperature of 230° Fahrenheit, until a sample weighed on a scale
remains constant. The loss of weight indicates the degree of humidity.
To determine the ash percentage, the sample is placed in a platinum
crucible, and held over a lamp until all the organic matter is burned
out and the ash has assumed a light color. The cold ash is then
moistened with a carbonate of ammonia solution, and the crucible again
exposed until it is dark red; the weight of the ash is then taken. To
determine the percentage of wool, a sample of the paper is dried at
230° Fahrenheit and weighed, boiled in a porcelain dish in potash lye
12° B. strong, and frequently stirred with a glass rod. The wool fiber
soon dissolves in the potash lye, while the vegetable fiber remains
unaltered. The pulpy mass resulting is placed upon a filter, dried at
212° Fahrenheit, and after the potash lye has dripped off, the
residue, consisting of vegetable fiber and earthy ash ingredients, is
washed until the water ceases to dissolve anything. The residue dried
at 212° Fahrenheit is weighed with a filter, after which that of the
latter is deducted. The loss of weight experienced is essentially
equal to the loss of the wool fiber. If the filtrate is saturated with
hydrochloric acid, the dissolved wool fiber separates again, and after
having been collected upon a weighed filter, it may be weighed and the
quantity ascertained.

The weight of the mineral substances in the raw paper is ascertained
by analyzing the ash in a manner similar to that above described. The
several constituents of the ash and the mineral added to the raw paper
are ascertained as follows: Sufficient of the paper is calcined in the
manner described; a known quantity of the ash is weighed and thrown
into a small porcelain dish containing a little distilled water and an
excess of chemically pure hydrochloric acid. In this solution are
dissolved the carbonates, carbonate of lime, carbonate of magnesia, a
little of sulphate of alumina, as well as metallic oxides, while
silicate of magnesia, silicic acid, sulphate of lime (gypsum) remain
undissolved. The substance is heated until the water and excess of
free hydrochloric acid have been driven off; it is then moistened with
a little hydrochloric acid, diluted with distilled water and heated.
The undissolved residue is by filtering separated from the dissolved,
the filter washed with distilled water, and the wash water added to
the filtrate. The undissolved residue is dried, and after the filter
has also been burned in due manner and the ash added, the weight is
ascertained. It consists of clay, sand, silicic acid and gypsum.

The filtrate is then poured into a cylinder capable of holding 100
cubic centimeters, and furnished with a scale; sufficient distilled
water is then added until the well-shaken fluid measures precisely 100
cubic centimeters. By means of this measuring instrument, the filtrate
is then divided into two equal portions. One of these parts is in a
beaker glass over-saturated with chemically pure chloride of ammonia,
whereby any iron of oxide present and a little dissolved alumina fall
down as deposit. The precipitate is separated by filtering, washed,
dried at 212° Fahrenheit and weighed. To the filtrate is then added a
solution of oxalate of ammonia until a white precipitate of oxalate of
lime is formed. This precipitate is separated by filtering, washed,
dried and when separated from the filter, is collected upon dark
satinized paper; the filter itself is burned and the ash added to the
oxalate of lime. This oxalate of lime is then heated to a dark red
heat in a platinum crucible with lid until the oxalate of lime is
converted into carbonate of lime. By the addition of a few drops of
carbonate of ammonia solution and another slight heating of the
crucible, also the caustic lime produced in the filter ash by heating,
is reconverted into carbonate of lime, and after cooling in the
exsiccator, the whole contents of the crucible is weighed as
carbonate of lime, after deducting the known quantity of filter ash.

Any magnesia present in the filtrate of the oxalate of lime is by the
addition of a solution of phosphate of soda separated as phosphate of
ammonia and magnesia, after having stood twenty-four hours. The
precipitate is filtered off, washed with water to which a little
chloride of ammonia is added, dried, and after calcining the fiber and
adding the filter ash, glow heated in the crucible. The glowed
substance is weighed after cooling, and is pyrophosphate of magnesia,
from which the magnesia or carbonate of magnesia is calculated
stoichiometrically. All the ascertained sums must be multiplied by 2,
if they are to correspond to the analyzed and weighed quantity of ash.

The second half of the filtrate is used for determining the small
quantity of sulphate of lime still contained in the hydrochlorate
solution. By adding chloride of barium solution the sulphuric acid is
bound to the barytes and sulphate of baryta separates as white
precipitate. This is separated by filtering, washed, dried and weighed
in the customary manner. From the weight of the sulphate of baryta is
then computed the weight of sulphate of lime, which has passed over
into solution. The ascertained sum is also to be multiplied with 2.

The manufacture of roll tar paper from the roll paper was at first
found to be difficult, as it was impossible to submerge a surface
larger than from ten to fifteen square yards, rolled up, in the tar,
because more would have required too large a pan. Besides this, the
paper tears easily, when it is in the hot tar. All kinds of
experiments were tried, in order to impregnate the surface of the
paper without employing too large a pan.

The following method was tried at first: The roll paper was cut into
lengths of ten yards, which were rolled up loosely, so that a certain
space was left between the different coils. These loose rolls, of
course, occupied much space and could be put into the tar only in a
standing position, because in a horizontal one the several coils would
have pressed together again. The loose roll was therefore slipped over
a vertical iron rod fastened into a circular perforated wooden foot.
The upper end of this iron rod ended in a ring, in which the hook of a
chain or rope could be fastened. With the aid of a windlass the roll
was raised or lowered. When placed in the pan with boiling tar, it was
left there until thoroughly saturated. It was then taken out, placed
upon a table, and the excess of tar allowed to drip off into a vessel
underneath. After partially drying, the roll was spread out in open
air, occasionally turned, until sufficiently dried, when it was rolled
up again.

In order to neutralize the smeary, sticky condition of the surface and
avoid the disagreeable drying in open air, the experiment of strewing
sand on the sticky places was tried next. The weight of the paper was
largely increased by the sand, and appeared considerably thicker. For
this reason the method of sanding the paper was at once universally
adopted. To dispense with the process of permitting the surplus tar to
drip off, means were devised by which it was taken off by scrapers, or
by pressing through rollers. The scrapers, two sharp edged rods
fastened across the pan, were then so placed that the paper was drawn
through them. The excess of tar adhering to its surface was thereby
scraped off and ran back into the pan.

This work, however, was performed better and to more satisfaction by a
pair of rollers fastened to the pan. These performed a double duty;
thoroughly removed the tar from the surface and by reason of their
pressure they caused a more perfect incorporation of the tar with the
fibers of the paper. Finally, different factories employed different
methods of manufacture, one of which was to cut the rolls into
definite lengths of about ten yards; these were then rerolled very
loosely and immersed in the hot tar until sufficiently saturated. The
paper was then passed through the roller, much pressure exerted, and
then loosely rolled up again. Being tarred once, it was then laid into
a second pan with hot tar, reeled out after a time, strewn with sand,
and rolled up again. Another method was to cut clothes lines into
lengths of about fifteen yards, and at a distance of two inches have
knots tied in them. The paper was cut in lengths of ten or fifteen
yards, three pieces of the knotted clothes line were then rolled
between the loose coils of paper, which was then submerged in the tar,
which on account of the knots could penetrate the paper. The paper was
next sanded by permitting its lower surface to pass over dry sand in a
box standing on the floor. A workman rolled off the paper, and with
his hand he strews sand on the upper surface. The rolling taking place
on the edge of a table, by means of a crank, the excess of sand
dropped off.

It is said by this method two workmen, one of which tends to the
rolling and sanding, the other turning the crank, could turn out
eighty rolls per day. This method is still in use. It is useless to
describe the many antiquated methods in vogue in smaller factories,
and it can truthfully be said that nearly all of them are out of date.
It appears to be the fact of almost all inventions that when reduced
to practical use, the arrangements, apparatus, and working methods
employed are generally of the most complicated nature, and time and
experience only will simplify them. This has been also the case with
the methods in the roofing paper industry, which are at present
gradually being reduced to a practical basis. The method gradually
adopted has been described in the preceding. The pan is of a certain
length, whereby it becomes possible to saturate the paper by slowly
drawing it through the heated tar. This is the chief feature. The work
is much simplified thereby and the workmen need not dip their hands
into the tar or soil them with it. The work of impregnating has become
much cleaner and easier, while at the same time the tar can be heated
to a much higher temperature. The pan is generally filled with
distilled coal tar, and the heating is regulated in such a manner that
the temperature of the impregnating mass is raised far beyond 212°
Fahrenheit. This accelerates the penetration, which takes place more
quickly as the degree of heat is raised, which may be almost up to the
boiling point of the tar, as at this degree the paper is not destroyed
by the heat. In order to prevent the evaporation of the volatile
ingredients of the tar, the pan is covered with a sheet iron cover,
with a slot at the place where the paper enters into the impregnating
mass and another at the place where it issues. The tar is always kept
at the same level, by occasional additions.

The roll of paper is mounted upon a shaft at the back end of the pan,
and by suitable arrangement of guide rollers it unwinds slowly, passes
into the tar in which it is kept submerged. The guide rollers can be
raised so that when a new roller is set up they can be raised out of
the tar. The end of the paper is then slipped underneath them above
the surface of the tar, when having passed through the squeezing
rollers, it is fastened to the beaming roller, and the guide rollers
are submerged again. A workman slowly turns the crank of the beaming
roller.

This motion draws the paper slowly through the fluid, the roll at the
back end unwinding. The speed with which the squeezing rollers are
turned is regulated in such a manner that the paper remains
sufficiently long underneath the fluid to be thoroughly impregnated
with it. The workmen quickly learn by experience how fast to turn the
crank. The hotter the tar, the more rapid the saturation; the high
degree of heat expels the air and evaporates the hygroscopic fluid in
the pores of the paper. The strong heating of the tar causes another
advantage connected with this method. The surface of the paper as it
issues from the squeezing rollers is still very hot, and a part of the
volatile oils evaporate very quickly at this high temperature. The
surface is thereby at once dried to a certain degree and at the same
time receives a handsome luster, as if it had been coated with a black
lacquer. The paper is sanded in a very simple manner without the use
of mechanical apparatus; as it is being wrapped into a coil, it passes
with its lower surface over a layer of sand, while the workman who
tends to rolling up strews the inside with sand. The lower surface is
coated very equally. Care only being necessary that the sand lies
smooth and even at all times. When the workman has rolled up ten or
fifteen yards, he cuts it across with a knife and straightedge, so
that the paper is cut at right angles with its sides.

There are three different sorts of roofing paper, according to the
impregnating fluid used in its manufacture. The ordinary tar paper is
that saturated with clear cold tar. This contains the greatest amount
of fluid ingredients and is very raggy in a fresh condition. It is
easy to see that the volatile hydrocarbons evaporate in a short time,
and when expelled, the paper becomes stiffer and apparently drier.
This drying, or the volatilization of the hydrocarbons, causes pores
between the fibers of the paper. These pores are highly injurious to
it, as they facilitate a process of decomposition which will ruin it
in a short time.

Roofing paper can be called good only when it is essentially made from
woolen rags, and contains either very few or no earthy additions. It
is beyond doubt that the durability of a roofing paper increases with
the quality of wool fiber it contains--vegetable fibers and earthy
additions cause a direct injury. Reprehensible altogether is any
combination with lime, either in form of a carbonate or sulphate,
because the lime enters into chemical combination with the
decomposition products of the tar.

The general nature of gravel is too well known to require description.
The grains of quartz sand are either sharp cornered or else rounded
pieces of stone of quartz, occasionally mixed with grains of other
amorphous pieces of silica--such as horn stone, silicious slate,
carnelian, etc.; again, with lustrous pieces of mica, or red and white
pieces of feldspar. The gravel used for a tar paper roof must be of a
special nature and be prepared for the purpose. The size of its grains
must not exceed a certain standard--say, the size of a pea. When found
in the gravel bank, it is frequently mixed with clay, etc., and it
cannot be used in this condition for a roof, but must be washed. The
utensils necessary for this purpose are of so simple and suggestive a
nature that they need not be described. Slag is being successfully
used in place of the gravel. It is easily reduced to suitable size, by
letting the red hot mass, as it runs from the furnace, run into a
vessel with water. The sudden chilling of the slag causes it to burst
into fragments of a sharp cornered structure. It is next passed
through a sieve, and the suitably sized gravel makes an excellent
material, as it gives a clean appearance to the roof.

The thinking mind can easily go one step further and imagine that,
since the tar contains a number of volatile hydrocarbons, it might be
made more adaptable for impregnation by paper by distilling it, as by
this process the fluid would lose its tendency to evaporate and the
percentage of resinous substances increase. Singular to say, there was
a prejudice against the employment of distilled tar, entertained by
builders and people who had no knowledge of chemistry. Increasing
intelligence and altered business circumstances, however, brought
about the almost universal employment of distilled tar, and every
large factory uses it at present. The roofing paper prepared with
distilled tar is perhaps most suitably called asphaltum paper, as this
has been used in its manufacture. It possesses properties superior to
the ordinary tar paper, one of which is that immediately after its
manufacture, as soon as cold, it is dry and ready for shipment; nor
does it require to be kept in store for a length of time, and it has
also a good, firm body, being as flexible and tough as leather. It is
very durable upon the roof, and remains flexible for a long time. It
is true that asphaltum papers will always in a fresh state contain a
small percentage of volatile ingredients, which after a while make it
hard and friable upon the roof; but, by reason of its greater
percentage of resinous components, it will always preserve a superior
degree of durability and become far less porous. One hundred parts by
weight absorb 140 or 150 parts by weight of coal tar. A factory which
distilled a good standard tar for roofing paper recovered, besides
benzole and naphtha, also about ten per cent. of creosote oil, used
for one hundred parts raw paper, 176.4 partially distilled tar.
Experiments on a larger as well as a smaller scale reduced this
quantity to an average of 141.5 parts for one hundred parts raw paper.
The weight of sanded paper is very variable, as it depends altogether
upon the size of the sand grains. It may be stated generally that the
weight of the sand is as large as that of the tarred paper.

The kinds of roofing paper saturated with other additions besides coal
tar form a separate class, in order to neutralize the defects inherent
in coal tar. These additions were originally for the purpose of
thickening the paper and making it stiffer and drier. The most
ordinary and cheapest thickener was the coal pitch. Although the
resinous substances are increased thereby, still the light tar oils
remain to evaporate, and the paper prepared with such a substance
readily becomes hard and brittle. A better addition is the natural
asphaltum, because it resists better the destroying influence of the
decomposition process, and also, to a certain degree, protects the
coal tar in which it is dissolved. The addition of natural asphaltum
doubtless caused the name of "asphaltum roofing paper." Resin,
sulphur, wood tar and other substances were also used as additions;
each manufacturer kept his method secret, however, and simply pointed
out by high sounding title in what manner his paper was composed. In
most cases, however, this appellation was applied to the ordinary tar
paper; the impregnating substance was mixed only with coal pitch, or
else a roofing paper saturated with distilled tar. The costly
additions, by the use of which a high grade of roofing paper can
doubtless be produced, largely increased its price, and on account of
the constant fall of prices of the article, its use became rather one
of those things "more honored in the breach than in the observance,"
and was dispensed with whenever practicable. The crude paper is the
foundation of the roofing paper. The qualities of a good,
unadulterated paper have already been stated. At times, the crude
paper contains too many earthy ingredients which impair the cohesion
of the felted fibrous substance, and which especially the carbonate of
lime is very injurious, as it readily effects the decomposition of the
coal tar. The percentage of wool, upon which the durability of the
paper depends very largely, is very small in some of the paper found
in the market. In place of woolen rags, cheap substitutes have been
used, such as waste, which contains vegetable fibers. Since this
cannot resist the decomposition process for any length of time, it is
evident that the roofing paper which contains a noticeable quantity of
vegetable fibers cannot be very durable. To judge from the endeavors
made to improve the coal tar, it may be concluded that this material
does not fully comply with its function of making the roofing paper
perfectly and durably waterproof. The coal tar, be it either crude or
distilled, is not a perfect impregnating material, and the roofing
paper, saturated with it, possesses several defects. Let us in the
following try to ascertain their shortcomings, and then express our
idea in what manner the roofing paper may be improved. It was
previously mentioned that every tar roofing paper will, after a
greater or smaller lapse of time, assume a dry, porous, friable
condition, caused by the volatilization of a part of the constituents
of the tar. This alteration is materially assisted by the oxygen of
the air, which causes the latter to become resinous and exerts a
chemical influence upon them. By the volatilization of the lighter tar
oils, pores are generated between the fibers of the roofing paper,
into which the air and humidity penetrate. In consequence of the
greatly enlarged surface, not only the solid ingredients of the tar,
which still remain unaltered, are exposed to the action of the oxygen,
but also the fibers of the roofing paper are exposed to decomposition.
How destructive the alternating influence of the oxygen and the
atmospheric precipitations are for the roofing paper will be shown by
the following results of tests. It will have been observed that the
rain water running from an old paper roof, especially after dry
weather, has a yellowish, sometimes a brown yellow color. The
supposition that this colored rain water might contain decomposition
products of the roofing paper readily prompted itself, and it has been
collected and analyzed at different seasons of the year. After a
period of several weeks of fair weather during the summer, rain fell,
and the sample of water running from a roof was caught and evaporated;
the residue when dried weighed 1.68 grammes. It was of a brownish
black color, fusible in heat and readily soluble, with a yellow brown
color in water. The dark brown substance readily dissolved in ammonia,
alcohol, dilute acid, hydrochloric acid, sulphuric acid, and
decomposed in nitric acid, but did not dissolve in benzine or fat oil.
After several days' rain during the summer, a quantity of the water
was caught, evaporated, and the residue dried. Its characteristics
were similar to those above mentioned. By an experiment instituted in
water under conditions similar to the first mentioned, the dry brown
substance weighed 71 grammes. It possessed the same characteristics.
In the solution effected with water containing some aqua ammonia of
the brown substance, a white precipitate of oxalate of lime occurred
when an oxalate of ammonia solution was added, but the brown substance
remained in solution. A further precipitation of oxalate of lime was
produced by a solution of oxalic acid, but the brown organic substance
remained in solution. This organic substance being liberated from the
lime was evaporated, and left a dry, resinous, fusible brownish black
substance, which also dissolved readily in water. It will be seen from
these trials that the substance obtained from the rain water running
from a paper roof is a combination of an organic acid with lime, which
readily dissolves in water, and that also the free organic acid
combined with the lime dissolves easily in water.

The question concerning the origin of this organic substance or its
combination with lime can only be answered in one way, viz., that it
must have been washed by the rain water out of the paper. But since
such a solid substance, easily soluble in water, is contained neither
in the fresh roofing paper nor in the coal tar, the only deduction is
that it must have arisen by the decomposition of the tar, in
consequence of the operation of the oxygen. The lime comes from the
coating substance of the roof, for which tar mixed with coal pitch was
used. The latter was fused with carbonate of lime. These analyses
furthermore show that the formation of the organic acid easily soluble
in water depends upon the season; and that a larger quantity of it is
generated in warm, sunny weather than in cold, without sunshine. This
peculiarity of the solid, resinous constituents of the coal tar, to be
by the operation of the atmospheric oxygen altered into such products
that are readily soluble in water, makes the tar very unsuitable as a
saturative substance for a roofing paper. How rapidly a paper roof can
be ruined by the generation of this injurious organic acid will be
seen from the following calculation: Let us suppose that an average
of 132 gallons of rain water falls upon ten square feet roof surface
per year, and that the arithmetical mean 0.932 of the largest (1.680)
and smallest number (0.184) be the quantity of the soluble brown
substance which on an average is dissolved in one quart of rain water;
hence from ten square feet of roof surface are rinsed away with the
rain water per year 466 grammes of the soluble decomposition products
of the tar. The oxidation process will not always occur as intensely
as by a paper roof, ten years old and painted two years ago, which
instigated above described experiment. As long as the roofing paper is
fresh and less porous, especially if the occurring pores are filled
and closed again by repeated coatings, oxidation will take place far
less rapidly. Besides this, the protective coating applied to the roof
surface is exposed most to this oxidation process. Even by assuming
this constantly progressive destructive action of the oxygen on the
roofing paper to be much less than above stated, we can readily
imagine that it must be quite large. If it is desired to produce a
material free of faults, it is first of all indispensable that
unobjectionable raw material be procured. Coal tar was formerly used
almost exclusively for the coating of a roof. It was heated and
applied hot upon the surface. In order to avoid the running off of the
thinly fluid mass, the freshly coated surface was strewn with sand.
The most volatile portion of the tar evaporated soon, whereby the
coating became thicker and finally dried. The bad properties of the
coal tar, pointed out elsewhere, made it very unsuitable even for this
purpose, and experiments were instituted to compound mixtures, by
adding other ingredients to the tar, that should more fully comply
with its function. It may be said in general that the coating masses
for roofs can be divided into two classes: either as lacquers or as
cements. To the former may be classed those of a fairly thinly fluid
consistency, and which contain volatile oils in such quantities that
they will dry quickly. Cements are those of a thickly fluid
consistency, and are rendered thus fluid by heating. It is not
necessary that the coating applied should harden quickly, as it
assumes soon after its application a firmness sufficient to prevent it
from running off the roof. Coal tar is to be classed among lacquers.
If it has been liberated by distillation from the volatile oils, it is
made better suited for the purpose than the ordinary kind. The mass
contains much more asphaltum, and after drying, which takes place
soon, it leaves a far thicker layer upon the roof surface, while the
pores, which had formed in the roofing paper consequent on drying, are
better filled up. Nevertheless, the distilled tar also has retained
the property of drying with time into a hard, vitreous mass, and
ultimately to be destroyed by decomposition.--_The Roofer_.

A PHYSICAL LABORATORY INDICATOR.

The difficulties attending the management of a physical laboratory are
much greater than those of a chemical one. The cause of this lies in the
fact that in the latter the apparatus is less complicated and the pieces
less varied. Any contrivance that will reduce the labor and worry
connected with the running of a laboratory is valuable.

A physical laboratory may be arranged in several ways. The apparatus may
be kept in a store room and such as is needed may be given to the
student each day and removed after the experiments are performed; or the
apparatus for each experiment or system of experiments may be kept in a
fixed place in the laboratory ready for assembling; for certain
experiments the apparatus may be kept in a fixed place in the laboratory
and permanently arranged for service.

Each student may have his own desk and apparatus or he may be required
to pass from desk to desk. The latter method is preferable.

When a store room is used the services of a man are required to
distribute and afterward to collect. If the apparatus is permanently
distributed, a large room is necessary, but the labor of collecting and
distributing is done away with.

There are certain general experiments intended to show the use of
measuring instruments which all students must perform. To illustrate the
use of the indicator I have selected an elementary class, although the
instrument is equally applicable to all classes of experiments.

Having selected a suitable room, tables may be placed against the walls
between the windows and at other convenient places. Shallow closets are
built upon these tables against the wall; they have glass doors and are
fitted with shelves properly spaced. A large number of light wooden
boxes are prepared, numbered from one up to the limit of the storage
capacity of the closets. A number corresponding to that upon the box is
placed upon the shelf, so that each one after removal may be returned to
its proper place without difficulty. On the front of the box is a label
upon which is written the experiment to be performed or the name of the
apparatus whose use is to be learned, references to various books, which
may be found in the laboratory library, and the apparatus necessary for
the experiment, which ought to be found in the box. If any parts of the
apparatus are too large to be placed in the box, the label indicates by
a number where it may be found in the storage case.

It is evident that, instead of the above arrangement, all the boxes can
be stacked in piles in a general store room. The described arrangement
is preferable, as it prevents confusion in collecting and distributing
apparatus when the class is large.

_The Indicator_ (see figure).--Some device is evidently desirable to
direct the work of a laboratory with the least trouble and friction
possible. I have found that the old fashioned "peg board," formerly used
in schools to record the demerits of scholars, modified as in the
following description, leaves nothing to be desired.

The requirements of such an instrument are these: It must show the names
of the members of the class; it must contain a full list of the
experiments to be performed; it must refer the student to the book and
page where information in reference to the experiments or apparatus may
be found; it must show what experiments are to be performed by each
student at a given time; it must give information as to the place in the
laboratory where the apparatus is deposited; it must show to the
instructor what experiments have been performed by each student; it must
prevent the assignment of the same experiment to two students; it must
enable the instructor to assign the same experiment to two or more
students; it must form a complete record of what has been done, what
work is incomplete, and what experiments have not yet been assigned; it
must also be so arranged that new experiments or sets of experiments may
be exhibited.

      +------+---+---+---+---+---+---+---+---+
      |      | A | B | C | D | E | F | G | H |
      +------+---+---+---+---+---+---+---+---+
      |    1 | *   o   o   *   o   o   o   o |
      |    2 | *   o   *   *   o   o   o   o |
      |    3 | +   *   *   *   o   o   o   o |
      |    4 | +   o   *   *   o   o   o   o |
      |    5 | o   +   *   *   *   *   o   o |
      |    6 | o   +   *   *   o   *   o   o |
      |    7 | o   o   +   *   o   o   o   o |
      |    8 | o   o   o   +   *   o   o   o |
      |    9 | o   o   o   *   +   o   o   o |
      |   10 | o   o   o   o   o   +   o   o |
      |   11 | o   o   o   *   o   o   +   * |
      |   12 | o   o   *   *   o   +   +   + |
      |   13 | o   o   *   o   o   o   o   o |
      |   14 | o   o   *   o   o   o   o   o |
      |   15 | o   o   +   o   o   o   o   o |
      |   16 | o   o   +   +   *   o   o   * |
      +--------------------------------------+

     A, B, C, etc., are cards upon which are the names of students. 1,
     2, 3, etc., are cards like the one described in the article. The
     small circles (o) represent unassigned experiments. The black
     circles (*) (slate nails) represent work done. The caudate circles
     (+) (brass nail) represent work assigned.

The indicator consists of a plank of any convenient length and breadth.
The front surface is divided into squares of such size that the pegs may
be introduced and withdrawn with ease. At each corner of the squares
holes are bored into which nails may be placed. There is a blank border
at the top and another on the left side. At the top of each vertical
column of holes is placed a card holder. This is made of light tin
turned up on the long edges--which are vertical--and tacked to the
board. Opposite each horizontal row of holes is a similar tin card
holder, but of greater length, and having its length horizontal. The
holders at the top of the board contain cards upon which the names of
the class are written.

Cards, like the following, are prepared for the horizontal holders.

--------------------------------------------------------------
Stewart & Gee 229
Physical Manip. 85    Intensity of Gravity--Borda's Method  39
Glazebrook & Shaw 132
--------------------------------------------------------------

These cards are numbered from one to any desired number and are arranged
in the holders consecutively.

Two kinds of nails are provided to fit the holes in the board: An
ordinary slate nail and a common picture frame nail with a brass head.
The latter indicates work to be done, the former work done.

To prepare the board for service, brass headed nails are placed opposite
each experiment, and below the names, care being taken not to have more
than one nail in the same horizontal row, unless it is intended that two
persons or more are to work upon the same experiment.

There will be no conflict when the brass nails occupy diagonal lines. If
they do not, a glance will show the fact.

After an experiment has been performed and a report made upon the usual
blank, the brass nail is removed and a slate nail put in its place.

The board will show by the slate nails what work has been done by each
student, by the brass nails what is yet to be done, and by the empty
holes, experiments which have been omitted or are yet to be assigned. A
slate nail opposite an experiment card indicates that that experiment
may now be assigned to another person.

It is evident that the schedule for a whole term may be arranged in a
few minutes and that the daily changes require very little time.

The board is hung in a convenient place. The student as he enters the
laboratory looks for his name on the upper cards and under it for the
first brass nail in the vertical column: to the left he finds the
experiment card. On the left hand end of the slip he sees the book
references, on the right hand end a number--39 in the sample card given
above. Knowing the number, he proceeds to a desk and finds a box
numbered in the same manner. He removes the box from the closet. On the
label of the box is a list of all the apparatus necessary, which he will
find in the box; the label also contains the book references. He
performs the experiment, fills up a blank which he gives to the
instructor, puts all the materials back in the box, replaces the box in
its proper place in the closet and proceeds with the next experiment.
With this indicator there is no difficulty in managing fifty students or
more.

Comparatively little apparatus need be duplicated. Where apparatus is
fixed against a wall a number may be tacked upon the wall and a card
containing the information desired. The procedure is then the same as
with the boxes. The cards on the board being removable, other ones may
be inserted containing information in reference to other boxes having
the same number but containing different materials. There can be no
successful tampering with the board, for the record of experiments
performed is upon the blanks which the students turn in and also in the
individual note books which are written up and given to the instructor
for daily examination.

Lafayette College. J.W. MOORE.

NEW METHOD OF EXTINGUISHING FIRES

This is by George Dickson, of Toronto, Canada, and David Alanson Jones.

A mixture of water and liquefied carbon dioxide upon being discharged
through pipes at high pressure causes the rapid expansion of the gas and
converts the mixture into spray more or less frozen, and portions of the
liquid carbon dioxide are frozen, owing to its rapid expansion, and are
thus thrown upon the fire in a solid state, where said frozen carbon
dioxide in its further expansion not only acts to put out the fire, but
cools the surface upon which it falls, and thus tends to prevent
reignition.

A represents a receptacle sufficiently strong to stand a pressure of not
less than a thousand pounds to the square inch.

B B water receptacles.

[Illustration: Fig. 1]

In the drawings we have shown two receptacles B and only one receptacle
A; but we do not wish to confine ourselves to any particular number, nor
do we wish to confine ourselves to the horizontal position in which the
receptacles are shown.

C is a pipe leading from the receptacle A to a point at or near the
bottom of the receptacle B.

F is a pipe through which the mixture of water and liquefied gas from
the receptacle B is forced by the expansion of said liquefied gas, the
said pipe taking the mixture of water and liquefied gas from the bottom
of the receptacle.

[Illustration: Fig. 2]

To use the apparatus, open the stop cock D in the pipe C, leading to one
of the receptacles B, whereupon, owing to the lower pressure in the
cylinder B, the liquid carbon dioxide expands and rises to the top of
the cylinder A and forces the liquid carbon dioxide into the cylinder B,
the same as the superior steam of a boiler forces the water of the
boiler out when the same is tapped below the surface of the liquid. Now
upon opening the tap H, this superior gas forces out the mixture of
water and liquid carbon dioxide, which suddenly expanding causes
portions of the globules of liquefied gas to be frozen, and these, being
protected by a rapidly evaporating portion of the liquefied gas, are
thrown on the fire in solid particles. At the same time the water is
blown into a spray, which is more or less frozen. The fire is thus
rapidly extinguished by the vaporization of the carbon dioxide and water
spray.

SMOKELESS GUNPOWDER.

BY HUDSON MAXIM.

During the last forty years leading chemists have continued to
experiment with a view to the production of a gunpowder which should be
smokeless. But not until the last few years has any considerable degree
of success been attained.

To be smokeless, a gunpowder must yield only gaseous products of
combustion. None of the so-called smokeless powders are entirely
smokeless, although some of them are very nearly so.

The smoke of common black gunpowder is largely due to minute particles
of solid matter which float in the air. About one-half of the total
products of combustion of black gunpowder of ordinary composition
consists of potassium carbonate in a finely divided condition and of
potassium sulphate, which is produced chiefly by the burning in the air
of potassium sulphide, another production of combustion, as on the
outrushing gases it is borne into the air in a fine state of division.

Another cause for the smoke of gunpowder is the formation of small
liquid vesicles which condense from some of the products of combustion
thrown into the air in a state of vapor, in the same manner as vesicles
of aqueous vapor form in the air on the escape of highly heated steam
from the whistle of a locomotive.

Broadly speaking, an explosive compound is one which contains, within
itself, all the elements necessary for its complete combustion, and
whose heated gaseous products occupy vastly more space than the original
compound. Such compound usually consists of oxygen, associated with
other elements, for which it has great affinity, and from which it is
held from more intimate union, or direct chemical combination, under
normal conditions, by being in combination as well with other elements
for which it has less affinity, but which it readily gives up for the
stronger affinities when explosion takes place, the other elements
either combining with one another to form new compounds or being set
free in an uncombined state.

An explosive is said to detonate when the above changes take place
instantaneously, the action being transmitted with the speed of
electricity by a sort of molecular rhythm from molecule to molecule
throughout the entire substance of the compound.

An explosive is said to explode when the above changes do not occur
instantaneously throughout the whole substance, but whose combustion
takes place from the surface inward of the particles or grains of which
it is composed, thus requiring some definite lapse of time.

The elements of an explosive compound may be associated chemically as in
nitro-glycerine and gun-cotton, which are chemical compounds, being the
results of definite reactions. Or, an explosive may be a mere mechanical
mixture of different substances comprising the necessary elements, as is
ordinary black gunpowder, which is a compound of charcoal, sulphur and
saltpeter, the saltpeter supplying the necessary oxygen.

No gunpowder can be smokeless in which saltpeter or any oxygen-bearing
salt having a metallic base is employed, for when the salt gives up its
oxygen, the base combines with other elements to produce a sulphate, a
carbonate, or other salt, which, being solid, produces smoke. Therefore,
to be smokeless, a gunpowder must contain no other elements than oxygen,
hydrogen, nitrogen, and carbon, and in such proportions that the
products of combustion shall be wholly gaseous. The nitric
ethers--gun-cotton and nitro-glycerine--constitute such explosive
compounds. These substances were formerly thought to be
nitro-substitution compounds, but are now known to belong to the
compound ethers of nitric acid.

Gun-cotton, discovered by Schonbein, in 1845, has since been looked upon
as the most promising material for a smokeless gunpowder, it being a
very powerful explosive and burning with practically no smoke. To-day,
gun-cotton, in some form or other, constitutes the base of substantially
all of the smokeless powders with which have been attained any
considerable degree of success.

Gun-cotton alone and in its fibrous state has been found to be too
quick, or violent, for propulsive purposes, such as use in firearms; as
under such conditions of confinement it is very likely to detonate and
burst the gun. However, if gun-cotton be dissolved in a suitable
solvent, which is capable of being evaporated out, such as acetone, or
acetate of ethyl, which are very volatile, it becomes, when thus
dissolved and dried, a very hard, horn-like, amorphous substance, which
may be used for a smokeless gunpowder. But this substance taken alone is
very difficult to mould or granulate, and the loss of expensive solvents
must necessarily be quite considerable.

When gun-cotton is reduced to a collodial solid, as above, and used as a
smokeless gunpowder, the grains must be made comparatively small to
insure prompt and certain ignition, and consequently the pressures
developed in the gun are apt to be too great when charges sufficiently
large are used to give desired velocities.

If, however, a compound be made of gun-cotton and nitro-glycerine, in
about equal parts, by means of a volatile solvent or combining agent,
such as one of the before mentioned, and the solvent evaporated out, we
obtain practically a new substance and one which, as regards its
explosive nature, is quite unlike either of its two constituents taken
alone. The nitro-glycerine, furthermore, being itself a solvent of
gun-cotton, much less of the volatile ether is necessary to render the
compound of an amorphous character. Being quite plastic this substance
may be wrought or moulded into any desired size or form of grain.

This simple compound of nitro-glycerine and gun-cotton, or with some
slight modifications, has been found, when properly granulated, to be
the most smokeless powder that has yet been discovered or invented. If
pure chemicals are employed in the manufacture, and the gun-cotton and
nitro-glycerine be made of the highest nitration and best quality, we
have a smokeless powder which will possess the following desirable
qualities:

1st. It is absolutely smokeless, that is, its products of combustion are
entirely gaseous.

2d. Its products of combustion are in no way deleterious or unpleasant.

3d. It is perfectly safe to manufacture, handle and transport. There is
no more danger of its exploding accidentally than there would be of an
explosion of shavings or sawdust; for, unless well confined and set off
with a strong primer, it will not explode at all. In the open its
combustion is so slow as to in no way resemble or partake of the nature
of an explosion.

4th. It is perfectly stable, and will keep any length of time absolutely
without undergoing any change whatever, under all conditions of
temperature or exposure to which gunpowder would ever be subjected.

5th. It is not hygroscopic, and may be soaked in water without being at
all affected by it.

6th. It will not corrode the cartridge case.

7th. It will not foul the gun.

8th. It is sure of ignition with a good primer, and may be made to burn
as slowly as desired by varying the character and size of the grains.
Indeed, it may be made to burn so slowly as to fail of complete
combustion before the bullet leaves the gun, and after firing several
rounds, partly burned pieces of the powder may be picked up in front of
the gun.

9th. In a shoulder arm, a velocity of 2,000 feet per second may be
imparted to the bullet with this powder, and with a pressure in the
chamber of the gun of not more than fifteen English tons. This is, of
course, when the gun, cartridge case, primer, and projectile are adapted
to the use of smokeless powder, and the granulation of the powder is
adapted to them.

If what I have here claimed for the above smokeless powder be true, it
would appear that it may be taken as really an ideal smokeless powder.
Why, then, has it not already been universally adopted? Surely such a
powder is just what every government is seeking. In reply to this, let
me say that, in order for the above compound to be an effective and
successful smokeless powder, with the manifestation of the many
desirable qualities which I have recited, a great many other conditions
are necessary, some of which I will mention. To arrive at the knowledge
that this compound would constitute the best smokeless powder has
required a great deal of experimenting. It was first thought that
gun-cotton colloid, without any nitro-glycerine, that is, gun-cotton
dissolved and dried, would burn more slowly, keep better, and give
better ballistics than it would if combined with nitro-glycerine. It was
also thought that gun-cotton of a high degree of nitration when made
into colloidal form would even then burn too quickly to be suitable for
use in firearms. Consequently, the first experiments were with low grade
gun-cotton, what is called collodion cotton, such as is employed in the
manufacture of celluloid. But, as this would not explode without the
addition of some oxygen-bearing element, various oxygen-bearing salts
were combined with it, such as nitrate of potassium, nitrate of ammonia,
nitrate of baryta, etc. Also a great many of the first smokeless powders
were made of low grade gun-cotton combined with nitro-glycerine in
varying proportions. These powders would often give very good results
when first made; but low grade gun-cotton or di-nitro-cellulose, as it
is called, is a very unstable compound, and these powders, after giving
very promising results, were found to be constantly undergoing change,
sooner or later resulting in complete decomposition.

When nitro-glycerine was first combined with gun-cotton in small
quantities, camphor was often added, to lessen the rapidity of
combustion which the nitro-glycerine was supposed to impart and also to
render the compound more plastic, and to tend to prevent the
decomposition of the low grade gun-cotton. But camphor being volatile,
would, by its evaporation, cause the powder to constantly change in
character. Castor oil has been found to be a better diluent, as this
will not evaporate.

As all of the smokeless powders made of a low grade gun-cotton were
found to deteriorate and spoil, experiments were made with gun-cotton of
the highest degree of nitration, both alone and in combination with
nitro-glycerine. These experiments were first conducted in England by
private parties and by the British government, when it was found that
high grade gun-cotton would give excellent results if made into a
colloidal solid and used alone, or in combination with certain other
constituents. With a view to saving the large quantity of solvents
necessary to reduce the gun-cotton, and to get a more prompt and certain
ignition with a larger grain, experiments were cautiously made by the
admixture of varying proportions of nitro-glycerine to the gun-cotton
when dissolved, or rather along with other solvents in the process of
dissolving it.

It was soon found that nitro-glycerine added in quantities, even equal
in weight to the gun-cotton itself, did not materially increase the
rapidity of the explosion of the compound. And it was also found that
high grade gun-cotton, when combined with nitro-glycerine, gave very
much better results than low grade gun-cotton.

I have spoken here of high and low grade gun-cotton, when in fact the
word gun-cotton should be applied only to the highest nitro-compound of
cellulose. The word gun cotton has always been rather loosely used.
Pyroxyline would be a better word, as this applies to all grades. When
cotton fiber is soaked in a large excess of a mixture of the strongest
nitric and sulphuric acids, gun-cotton proper, or that of the highest
grade, is produced. When weaker acids are used, lower grades of
nitro-cellulose are formed.

The first mentioned or highest grade gun-cotton, when thoroughly freed
from its acids, has always proved to be a perfectly stable compound. The
lower grades have always been found to be unstable and subject to
spontaneous decomposition. Nitro-glycerine has also been erroneously
thought to be a very unstable compound. But experiments have proved
that, when made pure, it is perfectly stable.

Having now explained how the knowledge came to be arrived at that the
aforementioned compound of highest grade nitro-glycerine and highest
grade gun-cotton would constitute the best basis for a smokeless powder,
I will now mention a few of the other conditions necessary to success
with its use, without assuming that smokeless powder has yet passed its
experimental stage, and is beyond further improvement. Nevertheless,
such is the compound which has come to stay as the basis of all
smokeless powders; and any smokeless powder, if a successful one, may be
counted upon as being made of this compound of gun-cotton and
nitro-glycerine, or of a colloid of gun-cotton, either alone or combined
with diluents, oxygen-bearing salts, or inert matter. The fact that
smokeless powder may still be said to be in somewhat of an experimental
stage is not to admit that it is not a success. Firearms, cartridge
cases, and projectiles are also still in an experimental stage, for they
are constantly being improved; yet their use has been a great success
for a good many years.

The question of success of a smokeless powder does not rest alone with
the powder itself. The gun, the cartridge case, primer, and bullet have
been as much the subjects of experiments in adapting them to the use of
smokeless powder as has the smokeless powder in being adapted to them.
To impart a velocity of 2,000 feet per second to a rifle ball, with
corresponding long range and accuracy of flight, has been a question as
much of improvement in rifles and projectiles as in the powder. To give
a velocity of 2,000 feet per second to a bullet, requires a pressure of
at least 15 English tons in the chamber of a gun. This would be a
dangerous pressure in an old-fashioned shoulder arm; while a bullet made
only of lead would strip on striking the rifling and pass right through
the barrel of the gun without taking any rotary motion whatever. It
might at first seem that the powder is the only thing to be considered;
but high ballistics can only be obtained when everything else is adapted
to its use.

The projectile, the cartridge case, the fulminating cap, and the gun
have had to be all built up together, and a very large amount of
experimenting has been necessary to determine what would constitute the
best projectile, best cartridge case, best fulminating cap, and what
should be the character of the rifling and the quality and temper of the
steel of the gun barrel.

It has been necessary first to conduct experiments to test the smokeless
powders for velocities and pressures, and then with the powders test
various kinds of projectiles and guns. In order to obtain the high
ballistics which have been secured, it has been found necessary to cover
the bullet with something harder than lead and to rifle the gun in a
special manner.

The French, who were the first to definitely adopt smokeless powder,
were the first also to make a rifle, projectile, cartridge case and
primer suited to its use.

To obtain long range with a small long bullet such as is now used, it
should rotate at a very high speed. It is well known to artillerists
that a projectile of four or more calibers in length has to be rotated
at a much higher speed than one of half that length, in order to keep
the projectile stiff in the air, and to prevent it from ending over in
its flight. To communicate this very high rotary movement to the bullet
in the instant of time during which it is passing through the barrel,
the rifling of the gun has to exert an enormous torsion on the bullet.
Lead, no matter how hardened, is not sufficiently strong, as it will not
only strip and pass straight through the gun without taking any rotary
movement whatever, but under such very high pressures it behaves like
wax, and is thrown from the gun in a distorted mass.

The French cover their bullets with German silver, a substance made of
nickel, zinc and copper; and in order to put as little strain upon the
rifling and projectile as possible, the rifling of the gun is made with
an increasing twist, and has no sharp edges. The French rifle is made
very strong at the breech and is of tempered steel throughout. In this
way the French have made smokeless powder a success--a smokeless powder
made substantially of a character such as I have herein described. With
smokeless powder, the French rifle imparts a muzzle velocity of 2,000
feet per second to the bullet, with a range of about 2,400 meters.

If smokeless powder be divided into sufficiently small grains to be
ignited by an ordinary fulminating cap, it would burn too quickly,
thereby causing the pressure to mount too high, and without giving the
desired velocity. Consequently very large and strong fulminating caps
have to be employed. Smokeless powder is not ignited in the same manner
as black powder. Something besides ignition is necessary. Black powder
simply requires to be set on fire; while a smokeless powder, on the
contrary, not only requires that it be set on fire, but that a certain
degree of pressure be set up inside of the cartridge case. For instance,
if a primer of a certain size should be found to operate perfectly well,
giving prompt ignition in the cartridge case of a rifle of small
caliber, it would be found that the same primer would not ignite a
charge of the same powder if loaded into a gun of one inch caliber. In
the latter case a few grains only lying near the primer would be
ignited, and these would soon become extinguished by sudden release of
pressure bringing about a cooling effect due to expansion of the gases.
In small cartridges a large fulminating cap is all that is required, but
in large cartridges it is necessary to resort to additional means of
ignition.

In France, where experiments were conducted with a 37 millimeter Maxim
gun, it was found to be impracticable to use a fulminating cap
sufficiently large to ignite the powder and cause it to burn. Therefore,
a small ignition charge of black powder was employed, it being put in a
capsule or bag and placed next the primer. On firing at the rate of 300
rounds per minute, the black powder, though small in quantity, produced
a cloud of smoke through which it was quite impossible to see. The
inventor of the gun then prepared for the French some wafers of
pyroxyline canvas, which were placed next to the primer, securing
thereby prompt ignition without the production of any smoke.

Smokeless powder, made as I have described, cannot be detonated by a
fulminating cap of any size or by any means whatever. A large charge of
fulminate of mercury placed inside the cartridge case next the primer
will not detonate the powder, it serving only to ignite it and cause it
to explode. But even this would not cause the powder to explode except
it be confined behind a projectile, that sufficient pressure may be run
up to make it burn in its own gases.

Some curious experiments with smokeless powder may be tried with a shot
gun. If the fulminating cap be large, the powder fine, the wads numerous
and hard and the charge of shot heavy, all being well rammed down, and
the paper case well spun over the last pasteboard wad, a charge of
smokeless powder about equal in weight to one-half of what would be
employed of black powder would give about the same results as black
powder. But if the charge of shot be omitted, the primer will only
ignite the powder, and there will be set up sufficient pressure merely
to throw the wads about half way up the barrel of the gun, when the
powder will go out. Now if this same charge of powder be collected and
reloaded into a new cartridge case and well confined behind wads and a
charge of shot, as above explained, it will all burn, giving the same
results as black powder.

Attempts have been made to use this powder in pistols and revolvers, but
here it has proved a failure, as the pressure is not great enough to
cause the powder to be consumed, unless it be in the form of very fine
grains or dust, in which case the pressure mounts too high. However,
this might be overcome to a degree by making the powder porous. The
chemical conditions of the powder might be the same, but the physical
conditions must be different. A powder suitable for shot guns and
pistols would not be suitable for rifles.

One not familiar with the characteristics of smokeless powder would be
almost certain to fail in his first attempt to fire it. Many persons
have been convinced by their first experiments that this powder would
not burn at all in a gun, any more than so much sand.

Smokeless powder is consumed with a rapidity which accords with the
conditions of its confinement. Therefore, the bullets which have been
experimented with by different governments have been the cause of much
of the varying pressures attributed to the smokeless powders.

The Austrians use the Mannlicher steel jacketed bullet. The steel casing
or jacket is first tinned on the inside and then the lead is cast in,
thus melting the tin and adhering firmly to the jacket. This projectile
sets up enormous friction in the barrel of the gun when used with
smokeless powder; as the smokeless powder leaves the gun barrel
perfectly clean and the two steel surfaces being in absolute contact
cause tremendous friction; and as the coefficient of friction varies
with every shot, the pressure in the gun constantly varies greatly.

The German silver covered bullet used by the French has the disadvantage
that when firing rapidly the chamber of the barrel becomes nickel plated
and great friction is caused, mounting up the pressures and causing the
muzzle velocities to fall off.

The Austrians, in order to prevent their steel cased bullets from
rusting and to lessen the friction in the barrel of the gun, cover them
with a heavy lubricant, which gives the cartridges an unsightly
appearance and causes them to gather dust and sand. The French employ a
lubricant at the base of the projectile, with a small copper disk
between the same and the powder.

Col. A.R. Buffington, commander of the National Armory at Springfield,
Mass., has made a steel covered projectile which he prevents from
rusting by blackening by a niter process. Several grooves are pressed in
the base of the bullet which carry a lubricant, and when the bullet is
inserted in the cartridge case the grooves are covered by it.
Furthermore, these grooves prevent the lead filling from bursting
through the steel casing, leaving the latter in the barrel, as often
occurs with the Austrian and French projectiles when using smokeless
powder.

A new projectile has lately come out, the invention of Captain Edward
Palliser, of the British army. This bullet consists of a jacket made of
very soft Swedish wrought iron, coated with zinc and filled with lead,
the lead being pressed into this jacket. The bullet is corrugated at its
base, after the manner of the one made by Colonel Buffington. This
projectile has been experimented with very extensively by the British
government, and at the works of the Maxim-Nordenfelt Guns and Ammunition
Company, in England. The zinc coating of the bullet is too soft to stick
to the barrel of the gun, and also in a measure acts as a lubricant.
This projectile has given better results than any other that has been
experimented with. The great velocities and the most uniform pressures
by the use of smokeless powder have been attained with this Palliser
bullet.

NOISELESSNESS.

A great many stories have been told about the noiselessness of smokeless
powder. But there is no such thing as a noiseless gunpowder. The report
of a gun charged with smokeless powder is very sharp, and is as loud as
when black powder is used, yet the volume of sound is much less, so that
the report cannot be heard at so great a distance.

The report of a gun using smokeless powder is a sound of much higher
pitch than when black powder is used, and consequently cannot be heard
at so great a distance as the lower notes given by black powder.

As smokeless powder exerts a much greater pressure than common black
powder when burned in a gun, one would naturally think that the recoil
of the barrel would be greater, owing to the greater pressure exerted by
the smokeless powder on the base of the cartridge case and the breech
mechanism. However, such is not the fact; for the barrel actually
recoils very much less when smokeless powder is used. This is due to the
suddenness with which the pressure is exerted by smokeless powder, it
acting more like a very sharp blow on the metal, whereby more of the
energy is converted into heat instead of being spent in overcoming the
inertia of the barrel to give recoil. Similarly when smokeless powder is
fired in a gun, the displacement of the air is so sudden that the sound
waves do not possess the same amplitude of recoil or vibration as is
given by black powder.

THE CONSTRUCTION AND MAINTENANCE OF UNDERGROUND CIRCUITS.

BY S.B. FOWLER.

The numerous disastrous storms of the last winter have brought out very
vividly the advantages of having all wires placed underground, and many
inquiries have been addressed to the companies operating underground
circuits as to their success. It is not probable that all of the answers
to these inquiries have been of the most favorable character. To many
central station managers an underground system means frequent
break-downs and interruptions of service, with, perhaps, slow and
expensive repairs, which bring in their turn numerous complaints, loss
of customers, and reduced profits. In many installations burn-outs both
underground and in the station are frequent, with the natural result
that the operating of circuits underground is not there considered an
unqualified success. The writer has in mind two very different
experiences with underground cables. Several miles of cable were bought
by a certain company, carefully laid, and up to to-day not a single
burn-out or interruption of service can be attributed to failure of
cables; at about the same time another company bought about an equal
amount of the same kind of cable, and in a comparatively short time the
current had to be shut off the lines and the whole installation repaired
and parts of it replaced. Both of these experiences have been repeated
many times and will be again, although it is simply a distinction
between a good cable properly laid and a good cable ruined by careless
and incompetent workmanship.

Every failure can be traced to poor work in the original installation or
to the use of a cheap cable, both causes being due, generally, to that
false economy which looks for too quick returns. A poorly insulated line
wire and a poorly insulated cable are two very different things.
However, it is a fact that by the use of a good cable it is not
difficult to construct an underground system for light, power, telegraph
or telephone uses that will be superior to overhead lines in its service
and in cost of maintenance. The ideal underground system must have as a
starting point a system of subways admitting of the easy drawing in and
out of cables and affording means of making subsidiary connections
readily and with the minimum of expense and interruption of service.
This is practically accomplished by a subway consisting of lines of pipe
terminating at convenient intervals, say at street intersections, in
manholes, for convenience in jointing and in running out house
connections. These pipes, or ducts, as they are called, should be for
two kinds of service; the lower or deeper laid lines for the main or
trunk circuits, and a second series of ducts laid nearer the surface,
running into service boxes placed near together for lines to "house to
house" connections. In some cities where it is allowed to run overhead
lines, the plan of running but one service connection in a block is
followed, all customers in the block being supplied from a line run over
the housetops or strung on the rear walls.

This makes unnecessary all subsidiary ducts except a short one from the
manhole to the nearest building in the block, and effects a considerable
saving in pipe, service boxes, cables and labor. The manholes should
have their walls built up of brick, the floors should be of concrete,
and there should be an inside lid which can be fastened down and the
manhole thus made water-tight.

For ducts wood, iron or cement lined pipe may be used. To preserve the
wood it is generally treated with creosote, which, in contact with the
lead cover of the cable, sets up a chemical action, resulting in the
destruction of the lead. Wood offers but little protection for the
cable, as it is too easily damaged and broken through in the frequent
street openings made by companies operating lines of pipe in the
streets, and as one of the main purposes of a subway is that of a
protection to cables, wooden ducts have little to recommend them except
their cheapness.

Iron pipes are either laid in trenches filled in with earth or are laid
in cement. Iron pipe will of course rust out in time, and if absolute
permanence in construction is desired, should be laid in cement, for
after the pipe rusts out, the duct of cement is still left. However, if
we are going to the expense of laying in cement, it would be much
preferable to use cement lined pipe, which is not only cheaper than iron
pipe, but makes the most perfect cable conduit, as it affords a
perfectly smooth surface to draw the cable over and give a good duct
edge.

It is not necessary, however, in small installations of cable,
especially where additional connections will not be of frequent
occurrence, to go to the expense of subways, for cable may be safely
laid in the ground in trenches filled in with earth, or can be inclosed
in a plain wooden box or a wooden box filled with pitch.

There are, of course, many localities where, if the cable is laid in
contact with the earth, a chemical action would take place which might
result in the destruction of the cable.

Underground cables are of the following classes: 1. Rubber insulated
cables, insulated with rubber or other homogeneous material. 2. Fibrous
cables, so called from the conductors being covered with some fibrous
material, as cotton or paper, which is saturated with the insulating
material, paraffine, resin oil, or some special compound. Under this
latter head is also included the dry core paper cables.

The first thing to do is to get the cable drawn into the ducts, and on
the proper accomplishment of this depends to a great extent the success
or failure of the whole installation. Probably the ducts have been wired
when the subway was constructed, but if not a wire must be run through
as a means of pulling in the draw rope. There are several kinds of
apparatus for getting a wire through a duct--rods, flexible tapes,
mechanical "creepers," etc.; but probably the best is the sectional rod.
This simply consists of three or four foot lengths of hard wood rods,
having metal tips that screw into each other. A rod is placed in a duct
at a manhole, one screwed to that, both are pushed forward, another one
added and pushed forward, and so on until they extend the entire length
of the duct. Then the wire is attached and the rods are pulled out and
detached one at a time and with the last rod the wire is through. At
least No. 14 galvanized iron or steel wire should be used, for any
smaller size cannot be used a second time, as a rule. In starting to
pull in the draw rope a wire brush should be attached to the wire and to
this again the rope, and when the brush arrives at the distant end of
the duct it very likely will bring with it a miscellaneous collection of
material which for the good of the cable had better be in the manhole
than in the duct.

The reel or drum carrying the cable should be mounted on wheels or jacks
and placed on the same side of the manhole as the duct into which the
cable is to be drawn, and must always be so placed that the cable will
run off the top of the reel.

There are several methods of attaching the draw rope to the cable. As
simple and strong a method as any is to punch two of these holes through
the cable, lead and all, and attach the rope by means of an iron
wire--some of the draw wire will do--run through these holes. Depending
on the length and weight of cable to be pulled it can be drawn either by
hand or by a multiplying winch. The rope should run through a block
fastened in the manhole in such a position that the rope shall have a
good straightaway lead from the mouth of the duct.

The strain on the cable should be perfectly uniform and steady; if the
power is applied by a series of jerks either the lead covering may be
pulled apart or some of the conductors broken. At the reel there must
always be a large enough number of men to turn it and keep the cable
from rubbing on anything, and in the manhole one or more men to see that
the cable feeds into the duct straight and to guide it if necessary. If
the ducts are of iron and are not perfectly smooth at the ends, these
should be made so with a file, and in addition a protector of some sort
should be placed in the mouths of the duct, both above and below the
cable. Six inches of lead pipe, split lengthwise and bent over at one
end to prevent being drawn into the duct with the cable, makes a very
good protector. The cable should be reeled off the drum just fast enough
to prevent any of the power used in pulling the cable through the duct
being utilized in unreeling it. If this latter is allowed to occur the
cable will be bent too short and the lead covering buckled or broken,
and also the cable may be jammed against the upper edge of the duct and
perhaps cut through.

If the reel is allowed to turn faster than the cable is drawn in, the
first three or four turns on the reel will slacken up, and the lead
covering may either be dented or cut through by scraping on the ground.
If the cable end when pulled through up to the block is not long enough
to bend around the hole more than half way, the rope should be
unfastened from its end, a length of rope with a well frayed out end
should be run through the block, and by fastening to the cable close to
the duct, with a series of half hitches, as much slack as necessary can
be pulled in. If this is properly manipulated there need not be a
scratch on the cable, but unless great care is taken the lead may be
pressed up into ridges and the core itself damaged.

Immediately after the cable is drawn in, if the joint is not to be at
once made, the open end or ends should be cut off and the cable soldered
up, as most cables are very susceptible to moisture and readily absorb
water even from the atmosphere. Where practicable it is always a good
plan to pull the cable through as many manholes as possible without
cutting the cable; for the joint is, especially in telephone or
telegraph cables, the weak point. To do this the rope should be pulled
through the proper duct in the next section without unfastening it from
the cable; the winch should be moved to the next manhole, and pulling
through then done as before. There should always be a man in every hole
through which the cable is running to see that it does not bind anywhere
and to keep protectors around the cable.

It is not advisable to pull more than one cable into a duct, and never
advisable to pull a cable into a duct containing another cable, but if
two or more cables have to go into the same duct, they should always be
drawn in together. Lead covered cables and those with no lead on the
outside should never be pulled into the same duct, for if they bind
anywhere the soft cable will suffer where two lead covered cables would
get through all right. Some manufacturers are now putting on their
cables a tape or braid covering, which saves the lead many bad bruises
and cuts, and is a valuable addition to a cable at very little
additional expense.

Practically all electric light and power cables are either single or
double conductors, and the jointing of these is comparatively a simple
matter, although requiring considerable care. The lead is cut back from
each end about four or five inches, and the conductors bared of
insulation for two or three inches. The bare conductors should be
thoroughly tinned by dipping in the metal pot or pouring the melted
solder over them. A sperm candle is better than resin or acid for any
part of the operations where solder is used. A lead sleeve is here
slipped back over the cable, out of the way, and the ends of the
conductors brought together in a copper sleeve which is then sweated to
a firm joint. This part must be as good a piece of work mechanically as
electrically. The bare splice is then wrapped tightly with cotton or
silk tape to a thickness slightly greater than that of the insulation of
the cable, and is thoroughly saturated with the insulating compound
until all moisture previously absorbed by the tape is driven off.

The lead sleeve is then brought over the splice and wiped to the cable.
The joint is then filled with the insulating compound poured through
holes in the top of the sleeve; these holes are then closed and the
joint is complete, and there is no reason why, in light and power
cables, that joint should not be as perfect as any other part of the
cable. When the cable ends are prepared for jointing they should be hung
up in such a position that they are in the same plane, both horizontal
and vertically, and firmly secured there, so that when the lead sleeve
is wiped on the conductor may be in its exact center, and great care
must be taken not to move the cables again until the sleeve is filled
and the insulation sufficiently cooled to hold the conductor in
position.

It is also very important to see that there are no sharp points on the
conductors themselves, on the copper sleeve, on the edges of the lead
covering or on the lead sleeve. All these should be made perfectly
smooth, for points facilitate disruptive discharges. Branch joints had
better be made as T-joints rather than as Y-joints, for they are better
electrically and mechanically, although they occupy more room in the
manholes. They are of course made in the same way as straight joints, a
lead T-sleeve being used, however. For multiple arc circuits copper
T-sleeves and for series circuits copper L-sleeves are used.

Telephone and telegraph cables are made of any required gauge of wire
and with from 1 to 150 conductors in a cable. In jointing these the
splices are never soldered, the conductors being joined either with a
twist joint or with the so-called Western Union splice. Each splice is
covered with a cotton or silk sleeve or a wrapping of tape, the latter
being preferable, although considerably increasing the time necessary
for making the joint. Great care must be taken that no ends of wire are
left sticking up, for they will surely work their way through the tape
and grounds, and crosses will be the result. The wires should always be
joined layer to layer and each splice very tightly taped in order to get
as much insulating compound around each splice as possible in the
limited space. The splices should be "broken" as much as possible, so as
to avoid having adjoining splices coming over each other. After the
joint has been saturated with insulating compound the wires should have
an outside wrapping of tape to keep them in shape, and then the sleeve
is wiped on and filled. If the insulation resistance of the jointed
telegraph or telephone cable is a quarter of what the cable tested in
the factory, it may be considered that an exceptionally good piece of
work has been done. I have spoken more particularly of fibrous lead
covered cables, as the handling of them includes practically every step
of the work on any other kind of underground cable. In insulating dry
core paper cables a paper sleeve is slipped over the splice, and in
rubber cables the splice is wrapped with rubber tape; all other details
are the same for these as for the fibrous cable.

In the laying of light and power cables every joint, as made, should be
tested for insulation with a Thomson galvanometer, as the insulation
must necessarily be very high, and if one joint or section of cable is
any weaker than another it may be very important in the future to know
it. All tests must be made after the joint has cooled, for while hot its
insulation resistance will be very low.

Tests for copper resistance should also be made to determine if the
splices are electrically perfect; an imperfect splice may cause
considerable trouble. In telegraph and telephone cables the conductors
should be of very soft copper, for in stripping the conductor of
insulation it is very easy to nick the wire, and if of hard drawn copper
open wires will be the result.

All work should be frequently tested for continuity with telephones,
magnetos, or small portable galvanometers. It is only necessary to
ground the conductors at one end and try each wire at the other end. For
this sort of work a telephone receiver used with one cell of some dry
battery is most convenient, and has the additional advantage of
affording a means of communication while testing, and is by far the best
thing for identifying and tagging conductors.

These cables should be frequently tested during the progress of the work
for grounds and crosses with a Thomson instrument, and when the cable is
complete, a careful series of tests of the capacity, insulation
resistance, and copper resistance of each wire should be made and the
exact condition of the cable determined before it is put in service, and
thereafter an intelligent oversight of the condition of the circuits
can thus be more readily maintained.

Where a company has extensive underground service, a regular cable gang
should be in its employ, for quick and safe handling of cables demands
the employment of men accustomed to the work. If the cable has been
properly laid and tests show it to be in good condition before current
is turned on, almost the only trouble to be anticipated will be due to
mechanical injury. Disruptive discharge, puncturing the lead, may occur;
but the small chance of its occurring can be greatly lessened by the use
of some kind of "cable protector," which will provide for the spark an
artificial path of less resistance than the dielectric of the condenser,
which the cable in fact becomes.

If a fault suddenly develops on a circuit, the chances are it will be
found in a manhole, and an inspection of the cable in the manhole will
generally reveal the trouble without resorting to locating with a
Wheatstone bridge. The cable is often cut through at the edge of the
duct, or damaged by something falling on it, or by some one "walking all
over it." To guard against these, the ducts should always be fitted with
protectors both above and below the cable. The cables should never be
left across the manholes, for they then answer the purpose of a ladder,
but should be bent, around the walls of the hole and securely fastened
with lead straps, that they may not be moved and the lead gradually worn
through.

In telegraph cables, when one or two conductors "go," it will probably
be useless to look for trouble except with instruments; but if several
wires are "lost" at once it will probably be found to be caused by
mechanical injury, which can be located by inspection. If it is ever
necessary to loop out conductors, a joint can be readily opened and the
conductors wanted picked out and connected into the branch cable and the
joint again closed without disturbing the working wires. In doing this a
split sleeve must be used, and the only additional precaution to be
taken is in filling the sleeve to have the insulating compound not hot
enough to melt the solder and open up the split in the sleeve. In
cutting in service on light and power cables it is entirely practicable
to do so without interruption of service on multiple arc circuits, even
those of very high voltage; but they require great precaution and
involve considerable risk to the jointer, and where possible the circuit
to which the connection is to be made should previously be cut dead.
Where the voltage is not dangerous to human life, almost any service
connection can be made without interruption of service.

I have only indicated a very few of the operations that may be found
necessary, and the probable causes of troubles that may be encountered
in the operating of underground circuits, believing that the different
problems that arise can, with a little experience, be successfully met
by any one who has a fair knowledge of the original construction of
cable lines.--_Electrical World_.

RAILROADS TO THE CLOUDS.

If George Stephenson, when he placed the first locomotive on the track
and guaranteed it a speed of six miles an hour, could have foreseen that
in less than eighty years the successors of his rude machine would be
climbing the sides of mountain ranges, piercing gorges hitherto deemed
inaccessible, crossing ravines on bridges higher than the dome of St.
Paul's, and traversing the bowels of the earth by means of tunnels, no
doubt his big blue eyes would have stood out with wonder and amazement.
But he foresaw nothing of the kind; the only problem present in his mind
was how to get goods from the seaports in western England to London as
easily and cheaply as possible, and to do this he substituted for
horses, which had for 150 years been drawing cars along wooden or iron
tracks, the wonderful machine which has revolutionized the freight and
passenger traffic of the world.

It was, indeed, impossible for any one to foresee the triumphs of
engineering which have accompanied the advances in transportation. To
the engineer of the present day there are no impossibilities. The
engineer is a wizard at whose command space and matter are annihilated.
The highest mountain, the deepest valley, has no terrors for him. He can
bridge the latter and encircle or tunnel the former. The only requisites
which he demands are that something in his line be needed, and that the
money is forthcoming to defray the expense, and the thing will be done.
But the railroad he is asked to construct must be necessary, and the
necessity must be plainly shown, or no funds will be advanced; and
although the theory does not invariably hold good, especially when a
craze for railroad building is raging, as a rule no expense for the
construction of a road will be incurred without a prospect of
remuneration.

Hence the need of railroad communication has caused lines to be
constructed through districts where only a few years ago the thing would
have been deemed impossible. The Pacific roads of this country were a
necessity long before their construction, and in the face of
difficulties almost insuperable were carried to successful completion.
So, also, of the railroads in the Andes of South America. The famous
road from Callao through the heart of Peru is one of the highest
mountain roads in the world, as well as of the most difficult
construction. The grades are often of 300 feet and more to the mile, and
when the mountains were reached so great were the difficulties the
engineers were forced to confront that in some places laborers were
lowered from cliffs by ropes in order that, with toil and difficulty,
they might carve a foothold in order to begin the cutting for the
roadway.

In some sections tunnels are more numerous than open cuts, and so far as
the road has gone sixty-one tunnels, great and small, have been
constructed, aggregating over 20,000 feet in length. The road attains a
height of 15,000 feet above the level of the sea, and at the highest
point of the track is about as high as the topmost peak of Mont Blanc.
It pierces the range above it by a tunnel 3,847 feet long. The stern
necessities of business compelled the construction of this road,
otherwise it never would have been begun.

The tunnels of the Andes, however, do not bear comparison with the
tunnels, bridges, and snow sheds of the Union Pacific, nor do even these
compare with the vast undertakings in the Alps--three great tunnels of
nine to eleven miles in length, which have been prepared for the
transit of travelers and freight. The requirements of business
necessitated the piercing of the Alps, and as soon as the necessity was
shown, funds in abundance were forthcoming for the enterprise.

But tunneling a mountain is a different thing from climbing it. Many
years ago the attention of inventors was directed to the practicability
of constructing a railroad up the side of a mountain on grades which, to
an ordinary engine, were quite impossible. The improvements in
locomotives twenty-five and thirty years ago rendered them capable of
climbing grades which, in the early days of railroad engineering, were
deemed out of the question. The improvements proved a serious stumbling
block in the way of the inventors, who found that an ordinary locomotive
was able to climb a much steeper grade than was commonly supposed. The
first railroads were laid almost level, but it was soon discovered that
a grade of a few feet to the mile was no impediment to progress, and
gradually the grade was steepened.

The inventors of mountain railroad transportation might have been
discouraged by this discovery, but it is a characteristic of an inventor
that he is not set back by opposition, which, in fact, only serves to
stimulate his zeal. The projectors of inclined roads and mountain
engines kept steadily on, and in France, Germany, England, and the
United States many experimental roads were constructed, each of a few
hundred yards in length, and locomotive models were built and put in
motion to the amazement of the general public, who jeered alike at the
contrivances and the contrivers, deeming the former impracticable and
the latter crazy.

But the idea of building a road up the side of a hill was not to be
dismissed. There was money in it for the successful man, so the cranky
inventors kept on at work in spite of the jeers of the rabble and the
discouragements of capitalists loath to invest their money in an
uncertain scheme. To the energy and perseverance of railroad inventors
the success of the mountain railroad is due, as also is the construction
of the various mountain roads, of which the road up Mt. Washington,
finished in 1868, was the first, and the road up Pike's Peak, completed
the other day, was the latest.

Of all the mountain roads which have been constructed since the one up
Mt. Washington was finished, the best known is that which ascends the
world-famous Rigi. With the exception of Mont Blanc, Rigi is, perhaps,
the best known of any peak in the Alps, though it is by no means the
highest, its summit being but 5,905 feet above the level of the sea.
Although scarcely more than a third of the height of some other
mountains in the Alps, it seems much higher because of its isolated
position. Standing as it does between lakes Lucerne, Zug, and Lowertz,
it commands a series of fine views in every direction, and he who looks
from the summit of Rigi, if he does no other traveling in Switzerland,
can gain a fair idea of the Swiss mountain scenery. Many of the most
noted peaks are in sight, and from the Rigi can be seen the three lakes
beneath, the villages which here and there dot the shores, and, further
on, the mighty Alps, with their glaciers and eternal snows.

Many years ago a hotel was built on the summit of the Rigi for the
benefit of the tourists who daily flocked to this remarkable peak to
enjoy the benefit of its wonderful scenery. The mountain is densely
wooded save where the trees have been cut away to clear the land for
pastures. The ease of its ascent by the six or eight mule paths which
had been made, the gradual and almost regular slope, and the throngs of
travelers who resorted to it, made it a favorable place for an
experiment, and to Rigi went the engineers in order to ascertain the
practicability of such a road. The credit of the designs is due to a
German engineer named Regenbach, who, about the year 1861, designed the
idea of a mountain road, and drew up plans not only for the bed but also
for the engine and cars. The scheme dragged. Capitalists were slow to
invest their money in what they deemed a wild and impracticable
undertaking, and even the owners of the land on the Rigi were reluctant
for such an experiment to be tried. But Regenbach persevered, and toward
the close of the decade the inhabitants of Vitznau, at the base of the
Rigi, were astonished to see gangs of laborers begin the work of making
a clearing through the forests on the mountain slope. They inquired what
it meant, and were told that a road up the Rigi was to be made. The
Vitznauers were delighted, for they had no roads, and there was not a
wheeled vehicle in the town, nor a highway by which it could be brought
thither. The idea of a railroad in their desolate mountain region, and,
above all, a railroad up the Rigi, never entered their heads, and a
report which some time after obtained currency in the town, that the
laborers were beginning the construction of a railroad, was greeted with
a shout of derision.

Nevertheless, that was the beginning of the Rigi line, and in May, 1871,
the road was opened for traffic. It begins at Vitznau, on Lake Lucerne,
and extends to the border of the canton and almost to the top of the
mountain. It is 19,000 feet long, and during that distance rises 4,000
feet at an average grade of 1 foot in 4. Though steep, it is by no means
so much so as the Mt. Washington road, which rises 5,285 feet above the
sea, at an average of 1 foot in 3. There are, however, stretches of the
Rigi road at which the grade is about 1 foot in 2½, which is believed to
be the steepest in the world.

The Rigi road has several special features aside from its terrific
slopes which entitle it to be considered a triumph of the engineer's
skill. About midway up the mountains the builders came to a solid mass
of rock, which presented a barrier that to a surface road was
impassable. They determined to tunnel it, and, after an enormous
expenditure of labor, finished an inclined tunnel 225 feet in length, of
the same gradient as the road. A gorge in the side of the mountain where
a small stream, the Schnurtobel, had cut itself a passage also hindered
their way, and was crossed by a bridge of lattice girder work in three
spans, each 85 feet long. The entire roadbed, from beginning to end, was
cut in the solid rock. A channel was chiseled out to admit the central
beam, which contains the cogs fitting the driving wheel of the
locomotive. The engine is in the rear of the train, and presents the
exceedingly curious feature of a boiler greatly inclined, in order that
at the steeper gradients it may remain almost perpendicular. The coal
and water are contained in boxes over the driving wheels, so that all
the weight of the engine is really concentrated on the cogs--a
precaution to prevent their slipping. The cost of the road, including
three of these strangely constructed locomotives, three passenger
coaches, and three open wagons, was $260,000, and it is a good paying
investment. The fare demanded for the trip up the mountains is 5 francs,
while half that sum is required for the downward passage, and the road
is annually traversed by from 30,000 to 50,000 passengers.

Curious sensations are produced by a ride up this remarkable line. The
seats of the cars are inclined like the boiler of the locomotive, and so
long as the cars are on a level the seats tilt at an angle which renders
it almost impossible to use them. But when the start is made the
frightful tilt places the body in an upright position, and, with the
engine in the rear, the train starts up the hill with an easy, gliding
motion, passing up the ascent, somewhat steeper than the roof of a
house, without the slightest apparent effort. But if the going up
excites tremor, much more peculiar are the feelings aroused on the down
grade. The trip begins with a gentle descent, and all at once the
traveler looking ahead sees the road apparently come an end. On a nearer
approach he is undeceived and observes before him a long decline which
appears too steep even to walk down. Involuntarily he catches at the
seats, expecting a great acceleration of speed. Very nervous are his
feelings as the train approaches this terrible slope, but on coming to
the incline the engine dips and goes on not a whit faster than before
and not more rapidly on the down than on the up grade. Many people are
made sick by the sensation of falling experienced on the down run. Some
faint, and a few years ago one traveler, supposed to be afflicted with
heart disease, died of fright when the train was going over the
Schnurtobel bridge. The danger is really very slight, there not having
been a serious accident since the road was opened. The attendants are
watchful, the brakes are strong, but even with all these safeguards, men
of the steadiest nerves cannot help wondering what would become of them
in case anything went wrong.

Bold as was the project of a railroad on the Rigi, a still bolder scheme
was broached ten years later, when a daring genius proposed a railroad
up Mt. Vesuvius. A railroad up the side of an ordinary mountain seemed
hazardous enough, but to build a line on the slope of a volcano, which
in its eruption had buried cities, and every few years was subject to a
violent spasm, seemed as hazardous as to trust the rails of an ordinary
line to the rotten river ice in spring time. The proposal was not,
however, so impracticable as it looked. While the summit of Vesuvius
changes from time to time from the frequent eruptions, and varies in
height and in the size of the crater, the general slope and contour of
the mountain are about the same to-day as when Vesuvius, a wooded hill,
with a valley and lake in the center of its quiescent crater, served as
the stronghold of Spartacus and his rebel gladiators. There have been
scores of eruptions since that in which Herculaneum and Pompeii were
overthrown, but the sides of the mountain have never been seriously
disturbed.

A road on Vesuvius gave promise of being a good speculation. Naples and
the other resorts of the neighborhood annually attracted many thousands
of visitors, and a considerable number of these every year ascended the
volcano, even when forced to contend with all the difficulties of the
way. Many, however, desiring to ascend, but being unable or unwilling to
walk up, a chair service was established--a peculiar chair being slung
on poles and borne by porters. In course of time the chair service
proved to be inadequate for the numbers who desired to make the ascent,
and the time was deemed fit for the establishment of more speedy
communication.

Notwithstanding the necessity, the proposal to establish a railroad met
with general derision, but the scheme was soon shown to be perfectly
practicable, and a beginning was made in 1879. The road is what is known
as a cable road, there being a single sleeper with three rails, one on
the top which really bore the weight, and one on each side near the
bottom, which supported the wheels, which coming out from the axle at a
sharp angle, prevented the vehicle from being overturned. The road
covers the last 4,000 feet of the ascent, and the power house is at the
bottom, a steel cable running up, passing round a wheel at the top and
returning to the engine in the power house. The ascent to the lower
terminus of the road is made on mules or donkeys; then, in a comfortable
car, the traveler is carried to a point not far from the crater. The car
is a combined grip and a passenger car, similar in some points to the
grip car of the present day, while the seats of the passenger portion
are inclined as in the cars on the Rigi road. But the angle of the road
being from thirty-three to forty-five degrees, makes both ascent and
descent seem fearfully perilous. Every precaution, however, is taken to
insure the safety of passengers; each car is provided with several
strong and independent brakes, and thus far no accident worth recording
has occurred. The road was opened in June, 1880. Although there have
been several considerable eruptions since that date, none of them did
any damage to the line but what was repaired in a few hours.

The fashion thus set will, no doubt, be followed in many other quarters.
Wherever there is sufficient travel to pay working expenses and a profit
on a steep grade mountain road it will probably be built. Already there
is talk of a road on Mont Blanc, of another up the Yungfrau, and several
have been projected in the Schwartz and Hartz mountains. A route on Ben
Nevis, in Scotland, is already surveyed, and it is said surveys have
also been made up Snowden, with a view to the establishment of a road to
the summit of the highest Welsh peak. Sufficient travel is all that is
necessary, and when that is guaranteed, whenever a mountain possesses
sufficient interest to induce people to make its ascent in considerable
numbers, means of transportation, safe and speedy, will soon be
provided. The modern engineer is able, willing and ready to build a road
to the top of Mt. Everest in the Himalayas if he is paid for doing
so.--_St. Louis Globe-Democrat._

To clean hair brushes, wash with weak solution of washing soda, rinse
out all the soda, and expose to sun.

THE MARCEAU.

[Illustration: THE FRENCH ARMORED TURRET SHIP MARCEAU]

The Marceau, the last ironclad completed and added to the French navy,
was put in commission at Toulon in April last, and has lately left that
town to join the French squadron of the north at Brest. The original
designs of this ship were prepared by M. Huin, of the French Department
of Naval Construction, but since the laying down of the keel in the year
1882 they have been very considerably modified, and many improvements
have been introduced.

Both ship and engines were constructed by the celebrated French firm,
the Société des Forges et Chantiers de la Mediterranée, the former at
their shipyard in La Seyne and the latter at their engine works in
Marseilles. The ship was five years in construction on the stocks, was
launched in May, 1887, and not having been put in commission until the
present year, was thus nearly nine years in construction. She is a
barbette belted ship of somewhat similar design to the French ironclads
Magenta, now being completed at the Toulon arsenal, and the Neptune, in
construction at Brest.

The hull is constructed partly of steel and partly of iron, and has the
principal dimensions as follows. Length, 330 ft. at the water line;
beam, 66 ft. outside the armor; draught, 27 ft. 6 in. aft.;
displacement, 10,430 English or 10,600 French tons. The engines are two
in number, one driving each propeller; they are of the vertical compound
type, and on the speed trials developed 11,300 indicated horse power
under forced and 5,500 indicated horse power under natural draught, the
former giving a speed of 16.2 knots per hour with 90 revolutions per
minute. The boilers are eight in number, of the cylindrical marine type,
and work at a pressure of 85.3 lb. per square inch. During the trials
the steering powers of the ship were found to be excellent, but the bow
wave is said, by one critic, to have been very great.

The ship is completely belted with Creusot steel armor, which varies in
thickness from 9 in. forward to 17¾ in. midships. In addition to this
belt the ship is protected by an armored deck of 3½ in., while the
barbette gun towers are protected with 15¾ in. steel armor with a hood
of 2½ in. to protect the men against machine gun fire. As a further
means of insuring the life of the ship in combat and also against
accidents at sea, the Marceau is divided into 102 water-tight
compartments and is fitted with torpedo defense netting. There are two
masts, each carrying double military tops; and a conning tower is
mounted on each mast, from either of which the ship may be worked in
time of action, and both of which are in telegraphic communication with
the engine rooms and magazines. Provision is made for carrying 600 tons
of coal, which, at a speed of 10 knots, should be sufficient to supply
the boilers for a voyage of 4,000 miles.

The armament of the Marceau is good for the tonnage of the ship and
consists principally of four guns of 34 centimeters (13.39 in.) of the
French 1884 model, having a weight of 52 tons, a length of 28½ calibers,
and being able to pierce 30 in. of iron armor at the muzzle. The
projectiles weigh 924 lb., and are fired with a charge of 387 lb. of
powder. The muzzle velocity has been calculated to be 1,968 ft. per
second. The guns are entirely of steel and are mounted on Canet
carriages in four barbette towers, one forward, one aft, and one on each
side amidships. On the firing trials both the guns and all the Canet
machinery, for working the guns and hoisting the ammunition, gave very
great satisfaction to all present at the time. In addition to the above
four heavy guns there are, in the broadside battery, sixteen guns of 14
centimeters (5.51 in.), eight on each side, and a gun of equal caliber
is mounted right forward on the same deck. The armament is completed by
a large number of Hotchkiss quick-firing and revolver guns and four
torpedo tubes, one forward, one aft, and one on each side.

The crew of the Marceau has been fixed at 600 men, and the cost is
stated to have been about $3,750,000.--_Engineering_.

[Continued from SUPPLEMENT, No. 820, page 13097.]

A REVIEW OF MARINE ENGINEERING DURING THE PAST DECADE.[1]

[Footnote 1: Paper read before the Institution of Mechanical Engineers,
July 28, 1891.]

BY MR. ALFRED BLECHYNDEN, OF BARROW-IN-FURNESS

_Steam Pipes_.--The failures of copper steam pipes on board the Elbe,
Lahn, and other vessels have drawn serious attention both to the
material and to the modes of construction of the pipes. The want of
elastic strength in copper is an important element in the matter; and
the three following remedies have been proposed, while still retaining
copper as the material. First, in view of the fact that in the operation
of brazing the copper may be seriously injured, to use solid drawn
tubes. This appears fairly to meet the main dangers incidental to
brazing; but as solid drawn pipes of over 7 inches diameter are
difficult to procure, it hardly meets the case sufficiently. Secondly,
to use electrically deposited tubes. At first much was promised in this
direction; but up to the present time it can hardly be regarded as more
than in the experimental stage. Thirdly, to use the ordinary brazed or
solid drawn tubes, and to re-enforce them by serving with steel cord or
steel or copper wire. This has been tried, and found to answer
perfectly. For economical reasons, as well as for insuring the minimum
of torsion to the material during manufacture, it is important to make
as few bends as possible; but in practice much less difficulty has been
experienced in serving bent pipes in a machine than would have been
expected. Discarding copper, it has been proposed to substitute steel or
iron. In the early days of the higher pressures, Mr. Alexander Taylor
adopted wrought iron for steam pipes. One fitted in the Claremont in
February, 1882, was recently removed from the vessel for experimental
purposes, and was reported upon by Mr. Magnus Sandison in a paper read
before the Northeast Coast Institution of Engineers and Shipbuilders.[2]
The following is a summary of the facts. The pipe was 5 inches external
diameter, and 0.375 inch thick. It was lap welded in the works of
Messrs. A. & J. Stewart. The flanges were screwed on and brazed
externally. The pipe was not lagged or protected in any manner. After
eight and a half years' service the metal measured where cut 0.32 and
0.375 inch in thickness, showing that the wasting during that time had
been very slight. The interior surface of the tube exhibited no signs of
pitting or corrosion. It was covered by a thin crust of black oxide, the
maximum thickness of which did not exceed 1/32 inch. Where the deposit
was thickest it was curiously striated by the action of the steam. On
the scale being removed, the original bloom on the surface of the metal
was exposed. It would thus appear that the danger from corrosion of iron
steam pipes is not borne out in their actual use; and hence so much of
the way is cleared for a stronger and more reliable material than
copper. So far the source of danger seems to be in the weld, which would
be inadmissible in larger pipes; but there is no reason why these should
not be lapped and riveted. There seems, however, a more promising way
out of the difficulty in the Mannesmann steel tubes which are now being
"spun" out of solid bars, so as to form weldless tubes.

[Footnote 2: Transactions Northeast Coast Institution of Engineers and
Shipbuilders, vol. 7, 1890-91, p. 179.]

TABLE I.--TENSILE STRENGTH OF GUN METAL AT HIGH TEMPERATURES.