Words pass along with meanings which are simple conventionalities,
marking current opinions, knowledge, fancies, and misjudgments. They
attain to new accretions of import as knowledge advances or opinions
change, and they are applied now to one set of ideas, now to another.
Hence there is nothing truer than the saying, "definitions are never
complete." The term explosion in its original introduction denoted
the making of a _noise_; it grew to comprehend the idea of _force_
accompanied with violent outburst; it is advancing to a stage in which
it implies _combustion_ as associated with destruction, yet somewhat
distinct from the abstract idea of the resolution of any form of matter
into its elementary constituents. The term, however, as yet takes in the
idea of combustion as a decomposition in but a very limited degree,
and it may be said to be wavering at the line between expansion and
dissociation.
Strictly, in insurance, fire and explosion are different phenomena.
A policy insuring against fire-loss does not insure against loss by
explosion. It thereby enforces a distinction which exists, or did exist,
in the popular mind; and fire, in an insurance sense, as distinct from
explosion, was accurately defined by Justice McIlvaine, of the Supreme
Court of Ohio (1872), in the case of the Union Insurance Company vs.
Forte, i.e., an explosion was a remote cause of loss and not the
proximate cause, when the _fire_ was a burning of a gas jet which did
not destroy, though the explosion caused by the burning gas-jet did
destroy. Earlier than this decision, however (in 1852), Justice Cushing,
of the Supreme Court of Massachusetts, in Scripture _vs_. Lowell Mutual
Fire Insurance Company, somewhat anticipated later definition, and
pronounced for the liability of the underwriter where all damage by the
explosion involves the ignition and burning of the agent of explosion.
That is, for example, the insurer is liable for damage caused by an
explosion from gunpowder, but not for an explosion from steam. The
Massachusetts Judge did not conceive any distinction as to fire-loss
between the instantaneous burning of a barrel of gunpowder and the
slower burning of a barrel of sulphur, and insurance fire-loss is not to
be interpreted legally by thermo-dynamics nor thermo chemistry. While
the legal principles are as yet unsettled, the tenor of current
decisions may be summed up as follows: If explosion cause fire, and fire
cause loss, it is a loss by fire as _proximate_ cause; and if fire cause
explosion, and explosion cause loss, it is a loss by fire as _efficient_
cause. Smoke, an imperfect combustion, damages, in an insurance sense,
as well as flame, which is perfect combustion; and where there is
concurrence of expanding air with expanding combustion, the law settles
on the basis of a common account. It's all "heat as a mode of motion."
Explosions are the resultants of elemental gases, vaporization,
comminution, contact of different substances, as well as of the
specifically named explosives. With new processes in manufacture,
involving chemical and mechanical transformations, and other uses of
new substances and new uses of old substances, explosions increase. The
flour-dust of the miller, the starch-dust of the confectioner, increase
in fineness and quantity, and they explode; so does the hop-dust of
the brewer. In 1844, for the first time, Professors Faraday and Lyell,
employed by the British government, discovered that explosion in
bituminous coal mines was the quickening of the comparatively slow
burning of the "fire-damp" by the almost instantaneous combustion of the
fine coal-dust present in the mines. The flyings of the cotton mill
do not explode, but flame passes through them with a rapidity almost
instantaneous, yet not sufficient to exert the pressure which explodes;
the dust of the wood planer and sawer only as yet makes sudden puffs
without detonating force. Naphtha vapor and benzine vapor are getting
into all places. One of the latest introductions is naphtha extracting
oil from linseed, and then volatilized by steam superheated to 400° F.
This combination reminds us, as to effectiveness, of the combination at
the recent Kansas City fire, when cans of gunpowder and barrels of coal
oil both went up together.
But it is the unsuspected causes of explosion which make the great
trouble, and prominent among these is conflagration as itself the
cause of explosion, and such explosion may develop gases which are
non-supporters of combustion as well as those which are inflammable.
You throw table salt down a blazing chimney to set free the
flame-suppressing hydrochloric acid, you discharge a loaded gun up a
blazing chimney to put out the fire by another agency; still the salt,
with certain combinations, may be explosive, a resinous vapor may be
combustive in a hydrochloric atmosphere, and gunpowder isn't harmless
when thrown upon a blaze--in fact, our common fire-extinguisher, water,
has its explosive incidences as liquid as well as vapor.
Gases explosive in association may be set free by the temperature of
a burning building and get together. In respect to the old conundrum,
"Will saltpetre explode?" Mr. A. A. Hayes, Prof. Silliman, and Dr.
Hare's views were, as to the explosions in the New York fire of 1845,
that in a closed building having niter in one part and shellac or other
resinous material in another, the gaseous oxygen generated from the
niter and the carbureted hydrogen from the resins mingling by degrees
would at length constitute an explosive mixture. A brief consideration
of specific explosives uniting may serve to illustrate this phase of the
subject.
Though the explosion of gunpowder is the result of a chemical change
whereby carbonic acid gas at high tension is evolved (due to the
saltpeter and the charcoal), the effect and rapidity of action are
greatly promoted by the addition of sulphur. On the contrary, dynamite,
now so important, and various similar explosives, are but mixtures of
nitro-glycerine with earthy substances, in order to diminish and make
more manageable the development of the rending force of the base. The
explosive power of any substance is the pressure it exerts on all parts
of the space containing it at the instant of explosion, and is measured
by comparing the heat disengaged with the volume of gas emitted, and
with the rapidity of chemical action. In the case of gunpowder, the
proper manipulation and division of the grains is important, because
favoring _rapid_ deflagration; but in a purely chemical explosion, each
separate molecule is an explosive, and the reaction passes from the
interior of one to the interior of another, suddenly driving the atoms
much further apart than their naturally infinitesimal vibrations.
Purely chemical explosives like nitro-glycerine, gun-cotton, the
picrites, and the fulminates, present a terrible danger from the unknown
mode of the new union of atoms, and reaction of the particles within
themselves, in spontaneous explosions happening in irregular manner.
Some curious circumstances attend the manufacture and use of
gun-cotton,[1] nitro-glycerine, and dynamite. Baron von Link, in his
system of the artillery use of gun-cotton, diminishes the danger of
sudden explosion by twisting the prepared cotton into cords or weaving
it into cloth, thereby securing a more uniform density. Mr. Abel's mode
of making gun-cotton, which explosive is now used more than any other by
the British government, includes drying the damp prepared cotton upon
hot plates, _freely open to the air_. If ignited by a flame, however, in
an unconfined place, gun-cotton only burns with a strong blaze, but
if _confined_ where the temperature reaches 340° F., it explodes with
terrific violence. Somewhat similar is the action of nitro-glycerine and
dynamite, which simply _burn_ if ignited in the open air, while the same
substance will _explode_ through a very slight concussion or by the
application of the electric spark; a red-hot iron, also, if applied,
will explode them when a flame will not. With care, nitro-glycerine can
be kept many years without deterioration; and it has been heated in a
sand-bath to 80° C. for a whole day without explosion or alteration. One
curious experiment is deserving of mention: If a broad-headed nail be
partly driven into pine wood, and then some pieces of dynamite placed on
the head of the nail, the latter may be struck hard blows with a wooden
mallet without exploding the dynamite _so long as the nail will continue
to enter the wood_.
[Footnote 1: The purest gun-cotton may be regarded as a _cellulose_,
in which three atoms of hydrogen are replaced by three molecules of
peroxide of nitrogen.]
Taking gunpowder as the unit, picrate of potash (picric acid and
potassium) has five times more force, gun-cotton seven and a half times,
and nitro-glycerine ten times more force. There are others still more
powerful, but less known and used, and some explosives are quite
uncontrollable and useless.
But the particular object of these remarks is to refer to articles of
merchandise non-explosive under general conditions, but so in particular
circumstances, as the two fire-extinguishers, water and salt, are
explosive under given conditions. The memorable fire which, in July,
1850, destroyed three hundred buildings in Philadelphia, upon Delaware
avenue, Water, Front, and Vine streets, was largely extended by
explosions of possibly concealed or unknown materials, the presence of
the generally recognized explosives being denied by the owners of the
properties.
"The germ of the first knowledge of an explosive was probably the
accidental discovery, ages ago, of the deflagrating property of the
natural saltpeter _when in contact with incandescent charcoal_."[1]
Although much manipulation is deemed necessary to form the close
mechanical mixture of the materials of gunpowder, it has never been
proved that such intimate previous union is necessary to precede the
chemical reaction causing explosion; indeed, some explosions in powder
works, before the mixture of the materials, or just at its commencement,
seem to point to the contrary. It is also certain that in the
manufacture of gunpowder the usual nitrate of potassium (saltpeter) can
be replaced by the nitrates of soda, baryta, and ammonia, also by the
chloride of potassium; charcoal by sawdust, tan, resin, and starch; and
though a substitute for sulphur is not easily found, the latter, or a
similar substance, is not an absolute necessity in the composition of
gunpowder.[2]
[Footnote 1: Encyclopædia Britannica, new edition, viii, p. 806.]
[Footnote 2: _Vide_ Abel's Experiments in Gunpowder, as detailed in
Phil. Trans. Eoy. Soc, 1874.--_Vide_ also _Bull. Soc. d'Encouragement_,
Nov., 1880, p. 633, _Sur les Explosives_.]
The generally received theory of the chemical action which makes
gunpowder explosive is that it is due to the superior affinity of the
oxygen of the niter (KNO_3) for the carbon of the charcoal, and the
production of carbonic acid gas (CO_2) and carbonic oxide (CO) suddenly
and in great volume. The latter extinguishes flame as well as the
former, unless its own flammability is supported by the oxygen of the
atmosphere until the degree of oxygenation CO_2 is reached. Considering
that water (H_2O) is composed of two volumes of hydrogen and one of
oxygen, and that under an enormously high temperature and the excessive
affinity of oxygen gas for potassium or sodium (freed from nitrate
union), dissociation of the water may be possible, aided by its being in
the form of spray and steam, we would hesitate to deny that an explosive
union of suitable crude salts could occur during the burning of a
building containing them when water for extinguishment was put on. Any
one who has seen the brilliance with which potassium and sodium burn
upon water can easily imagine how such strong affinity of oxygen for
these substances might aid in severing its union in water in their
presence and under extraordinary heat. It might be safe so say that the
presence of water under very high temperature may be as aidful to form
an explosive among such salts as have been named, as sulphur is for the
rapid combustion of gunpowder.
In the review for August, 1862 (Saltpeter Deflagrations in Burning
Buildings and Vessels--Water as an Explosive Agency), it was shown that
Mr. Boyden's experiments in 1861-62 proved that explosions would occur
when water was put upon niter heated alone, and stronger explosion from
niter, drywood, and sulphur; also explosion when melted niter was poured
on water. The following points we reproduce for comparison: If common
salt be heated separately to a bright heat, and water _at_ 150° F.
poured on it, an explosion will occur. Niter mixed with common salt,
placed upon burning charcoal, and water added, produce a stronger
explosion than salt alone. Heating caustic potash to a white heat, and
adding _warm or hot water_, produces explosion. At a Boston fire small
explosions were observed upon water touching culinary salt highly
heated. Anthracite coal and niter heated in a crucible exploded when
_sea water_ was poured on them.
The production of explosion by the putting of water on nitrate of
potassium and chloride of sodium arises from the union, at high
temperature, of the oxygen of the water with the potash and soda. Of the
three liberated gases, hydrogen only is inflammable, and the other two
suffocative of flame; but together the nitrogen and chlorine are not to
be undervalued, for chloride of nitrogen is ranked as the most terrible
and unmanageable of all explosives. Chlorine is a great water separator,
but in the present case its affinity for hydrogen would result in
hydrochloric acid, a fire extinguisher.
What happens in chemical experiment may be developed on a large scale in
burning grocery, drug, or drysalters' stores, when great quantities of
materials, such as just mentioned, including common salt, almost always
present, are heated most intensely, and then subjected to the action of
water in heavy dashes, or in form of spray or steam.
Picric acid, the nature of which we have several times previously
mentioned, and which explodes at 600° F. (only 28° above gunpowder), may
also be an element in such explosions during fires. Its salts form, in
combinations, various powerful explosives, much exceeding gunpowder
in force; and they have been used to a considerable extent in Europe.
Picric acid, now much employed by manufacturers and dyers for obtaining
a yellow color, is always kept in store largely by drysalters and
druggists, and generally by dyers, but in smaller quantity.
In a very destructive fire which occurred in Liverpool, Eng., in
October, 1874, involving the loss of several "fire-proof" stores,
repeated explosions of the vapor of turpentine rent ponderous brick
arched vaults, and exposed to the flames stocks of cotton, etc., in the
stories above. This conflagration was started by the carelessness of an
_employee_ in snuffing a tallow candle with his fingers and throwing the
burning snuff into the open bung-hole of a sample barrel of turpentine,
of which liquid there were many hundreds of barrels on storage in the
buildings. Turpentine vapor united with chlorine gas may not produce
explosion, but by spreading flames almost instantly throughout the
burning buildings, such burnings have practically equaled, if not
excelled, explosions, which may sometimes be fire-extinguishers. In such
cases detonation may be prevented by there being ample space to receive
the suddenly ignited vapor, lessening the tension of it, but carrying
the flames much more rapidly than otherwise to inflammable materials at
great distance.
If disastrous results have arisen from the vapor of turpentine as a fire
spreader in vaults without windows, it is possible that if a quantity of
hot water were suddenly converted into steam in closely confined spaces,
effects of pressure might be observed, less destructive perhaps, but
resembling those which other explosives might produce. If the immense
temperature attained in some conflagrations be considered--sufficient
to melt iron and vitrify brick--it is possible to conceive of water as
being instantly converted into steam. Even a very small quantity of
water thus expanded could produce most disastrous results. While such
formation of steam, if it happened, would certainly extinguish most
flames in direct contact, the general phenomena shown would be
explosive.
A curious circumstance occurred at the Broad street (N.Y.) fire in 1845,
previously mentioned. The fire extended through to Broadway, and almost
to Bowling Green. A shock like a dull explosion was heard, and by many
this was attributed to the effects of gunpowder and saltpeter. Several
firemen were, at the moment of the shock, on the roof of the burning
building, when the whole roof was suddenly raised and then let down
into the street, carrying the men with it uninjured. One of the firemen
described the sensation "as if the roof had been first _hoisted_ up
and then squashed down." _Query:_ Was this like the common lifting and
falling back of the loose lid of a tea-kettle containing boiling water?
Was it from steam--at a low pressure perhaps--seeking vent through the
roof in like manner to the raising of the kettle-lid? Without dilating
on this part of the subject, we mention it as a possible cause of minor
explosions--doubtless to become better known in future. It may even be
that explosions happening from steam acting in close spaces may have
been attributed to gunpowder, or to niter and other salts, separate, but
suddenly caused to combine in chemical reaction.--_American Exchange and
Review._
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