consequently upon this exemption a large business has grown up
in the preparation and use of dissolved acetylene for lighting
motor omnibuses, motor cars, railway carriages, lighthouses,
buoys, yachts, &c., for which it is particularly adapted.
Poisonous properties.
Acetylene was at one time supposed to be a highly poisonous
gas, the researches of A. Bistrow and O. Liebreich having
apoarently shown that it acts upon the blood in the same way
as carbon monoxide to form a stable compound. Very extensive
experiments, however, made by Drs N. Grehant, A. L. Brociner, L.
Crismer, and others, all conclusively show that acetylene is
much less toxic than carbon monoxide, and indeed than coal gas.
Chemical properties.
When acetylene was first introduced on a Commercial scale
grave fears were entertained as to its safety, it being
represented that it had the power of combining with certain
metals, more especially copper and silver, to form acetylides
of a highly explosive character, and-that even with coal
gas, which contains less than 1%, such copper compounds had
been known to be formed in cases where the gas-distributing
mains were composed of copper, and that accidents had
happened from this cause. It was therefore predicted that
the introduction of acetylene on a large scale would be
followed by numerous accidents unless copper and its alloys
were rigidly excluded from contact with the gas. These fears
have, however, fortunately proved to be unfounded, and ordinary
gas fittings can be used with perfect safety with this gas.
Acetylene has the property of inflaming spontaneously when
brought in contact with chlorine. If a few pieces of carbide
be dropped into saturated chlorine water the bubbles of
gas take fire as they reach the surface, and if a jet of
acetylene be passed up into a bottle of chlorine it takes
fire and burns with a heavy red flame, depositing its carbon
in the form of soot. If chlorine be bubbled up into a
jar of acetylene standing over water, a violent explosion,
attended with a flash of intense light and the deposition of
carbon, at once takes place. When the gas is kept in a small
glass holder exposed to direct sunlight, the surface of the
glass soon becomes dimmed, and W. A. Bone has shown that
when exposed for some time to the sun's rays it undergoes
certain polymerization changes which lead to the deposition
of a film of heavy hydrocarbons on the surface of the
tube. It has also been observed by L. Cailletet and later
by P. Villard that when allowed to stand in the presence
of water at a low temperature a solid hydrate is formed.
The polymerization of acetylene.
Acetylene is readily decomposed by heat, polymerizing under
its influence to form an enormous number of organic compounds;
indeed the gas, which can itself be directly prepared from its
constituents, carbon and hydrogen, under the influence of the
electric arc, can be made the starting point for the construction
of an enormous number of different organic compounds of a complex
character. In contact with nascent hydrogen it bunds up
ethylene; ethylene acted upon by sulphuric acid yields ethyl
sulphuric acid; this can again be decomposed in the presence
of water to yield alcohol, and it has also been proposed to
manufacture sugar from this body. Picric acid can also be
obtained from it by first treating acetylene with sulphuric
acid, converting the product into phenol by solution in
potash and then treating the phenol with fuming nitric acid.
Endothermic nature of acetylene.
Acetylene is one of those bodies the formation of which is
attended with the disappearance of heat, and it is for this
reason termed an ``endothermic'' compound, in contradistinction
to those bodies which evolve heat in their formation, and
which are called ``exothermic.'' Such endothermic bodies
are nearly always found to show considerable violence in
their decomposition, as the heat of formation stored up
within them is then liberated as sensible heat, and it is
undoubtedly this property of acetylene gas which leads to its
easy detonation by either heat or a shock from an explosion
of fulminating mercury when in contact with it under
pressure. The observation that acetylene can be resolved
into its constituents by detonation is due to Berthelot,
who started an explosive wave in it by firing a charge of
0.1 gram of mercury fulminate. It has since been shown,
however, that unless the gas is at a pressure of more than
two atmospheres this wave soon dies out, and the decomposition
is only propagated a few inches from the detonator. Heated
in contact with air to a temperature of 480 deg. C., acetylene
ignites and burns with a flame, the appearance of which
varies with the way in which it is brought in contact with the
air. With the gas in excess a heavy lurid flame emitting
dense volumes of smoke results, whilst if it be driven out
in a sufficiently thin sheet, it burns with a flame of
intense brilliancy and ulmost perfect whiteness, by the
light of which colours can be judged as well as they can by
daylight. Having its ignition point below that of ordinary
gas, it can be ignited by any red-hot carbonaceous matter,
such as the brightly glowing end of a cigar. For its
complete combustion a volume of acetylene needs approximately
twelve volumes of air, forming as products of combustion
carbon dioxide and water vapour. When, however, the air is
present in much smaller ratio the combustion is incomplete,
and carbon, carbon monoxide, carbon dioxide, hydrogen and
water vapour are produced. This is well shown by taking a
cylinder one-half full of acetylene and one-half of air; on
applying a light to the mixture a lurid flame runs down the
cylinder and a cloud of soot is thrown up, the cylinder also
being thickly coated with it, and often containing a ball of
carbon. If now, after a few moments' interval to allow
some air to diffuse into the cylinder, a taper again be
applied, an explosion takes place, due to a mixture of
carbon monoxide and air. It is probable that when a flame
is smoking badly, distinct traces of carbon monoxide are
being produced, but when an acetylene flame burns properly
the products are as harmless as those of coal gas, and,
light for light, less in amount. Mixed with air, like
every other combustible gas, acetylene forms an explosive
mixture. F. Clowes has shown that it has a wider range of
explosive proportions when mixed with air than any of the
other combustible gases, the limiting percentages being as
Acetylene . . . . . . . 3 to 82
Hydrogen . . . . . . . 5 to 72
Carbon monoxide . . . . 13 to 75
Ethylene . . . . . . . 4 to 22
Methane . . . . . . . . 5 to 13
Methods of production.
The methods which can be and have been employed from time to
time for the formation of acetylene in small quantities are
exceedingly numerous. Before the commercial production of
calcium carbide made it one of the most easily obtainable
gases, the processes which were most largely adopted for its
preparation in laboratories were:-first, the decomposition
of ethylene bromide by dropping it slowly into a boiling
solution of alcoholic potash, and purifying the evolved
gas from the volatile bromethylene by washing it through
a second flask containing a boiling solution of alcoholic
potash, or by passing it over moderately heated soda lime;
and, second, the more ordinarily adopted process of passing
the products of incomplete combustion from a Bunsen burner,
the flame of which had struck back, through an ammoniacal
solution of cuprous chloride, when the red copper acetylide
was produced. This on being washed and decomposed with
hydrochloric acid yielded a stream of acetylene gas. This
second method of production has the great drawback that,
unless proper precautions are taken to purify the gas obtained
from the copper acetylide, it is always contaminated with
certain chlorine derivatives of acetylene. Edmund Davy
first made acetylene in 1836 from a compound produced during
the manufacture of potassium from potassium tartrate and
charcoal, which under certain conditions yielded a black
compound decomposed by water with considerable violence and
the evolution of acetylene. This compound was afterwards fully
investigated by J. J. Berzelius, who showed it to be potassium
carbide. He also made the corresponding sodium compound
and showed that it evolved the same gas, whilst in 1862 F.
Wohler first made calcium carbide, and found that water
decomposed it into lime and acetylene. It was not, however,
until 1892 that the almost simultaneous discovery was made
by T. L. Willson in America and H. Moissan in France that if
lime and carbon be fused together at the temperature of the
electric furnace, the lime is reduced to calcium, which unites
with the excess of carbon present to form calcium carbide.
Manufacture of calcium carbide.
The cheap production of this material and the easy liberation
by its aid of acetylene at once gave the gas a position of
commercial importance. In the manufacture of calcium carbide
in the electric furnace, lime and anthracite of the highest
possible degree of purity are employed. A good working mixture
of these materials may be taken as being 100 parts by weight
of lime with 68 parts by weight of carbonaceous material.
About 1.8 lb. of this is used up for each pound of carbide
produced. The two principal processes utilized in making
calcium carbide by electrical power are the ingot process and
the tapping process. In the former, the anthracite and lime
are ground and carefully mixed in the right proportions to
suit the chemical actions involved. The arc is struck in a
crucible into which the mixture is allowed to flow, partially
filling it. An ingot gradually builds up from the bottom
of the crucible, the carbon electrode being raised from time
to time automatically or by hand to suit the diminution of
resistance due to the shortening of the arc by the rising
ingot. The crucible is of metal and considerably larger
than the ingot, the latter being surrounded by a mass of
unreduced material which protects the crucible from the intense
heat. When the ingot has been made and the crucible is
full, the latter is withdrawn and another substituted. The
process is not continuous, but a change of crucibles only
takes two or three minutes under the best conditions, and
only occurs every ten or fifteen hours. The essence of this
process is that the coke and lime are only heated to the
point of combination, and are not ``boiled'' after being
formed. It is found that the ingot of calcium carbide formed
in the furnace, although itself consisting of pure crystalline
calcium carbide, is nearly always surrounded by a crust
which contains a certain proportion of imperfectly converted
constituents, and therefore gives a lower yield of acetylene
than the carbide itself. In breaking up and sending out
the carbide for commercial work, packed in air-tight drums,
the crust is removed by a sand blast. A statement of the
amount made per kilowatt hour may be misleading, since a
certain amount of loss is of necessity entailed during this
process. For instance, in practical working it has been
found that a furnace return of 0.504 lb. per kilowatt hour
is brought down to 0.406 lb. per kilowatt hour when the
material has been broken up, sorted and packed in air-tight
drums. In the tapping process a fixed crucible is used,
lined with carbon, the electrode is nearly as big as the
crucible and a much higher current density is used. The
