and important facts into psychological science, and have illustrated and
extended some of the most interesting results of physiological research.
Let us trace the action of these substances, and explain it as far as
may be. Nitrous oxide, ether vapour, and chloroform vapour are all
soluble in watery fluids. The lungs present a vast surface bathed by
watery fluids, and therefore these gases are largely absorbed; and by a
well-known process, they pass directly into the blood, through the
delicate walls of the capillary vessels. The odour of ether can be
detected in any blood drawn from persons under its influence. Ether, or
chloroform, thus brought into the general current of the circulation, is
quickly carried to all parts of the body, and thus reaches the
nerve-centres. On these it produces characteristic effects by suspending
or paralysing nervous action: why or how this effect takes place is
unknown. The nervous centres are not all acted upon in an equal
degree—some require a larger quantity of the drug to affect them at all.
The parts of the nervous system first affected are the cerebral lobes,
which are known to be the seat of the intellectual powers. The
_cerebellum_—the function of which there is reason to believe is the
regulation and coordination of movements—is the next to yield to the
influence. Then follow the spinal nerves, which are the seat of
sensibility and motive power. This is as far as the action can safely be
carried: the nervous centre called the _medulla oblongata_, which is
placed at the junction of the brain and the spinal cord, still performs
its functions—one of the most important of which is to produce the
muscular contractions that keep the respiratory organs in action. We
have seen, by the effects of further etherization in animals, that when
this part of the system is affected, the animal dies from a stoppage of
the respiration.
But, unfortunately, there have been instances in which death has been
caused by the administration of ether and chloroform even under the most
skilful management. But these occurrences were not the result of the
inhalation having been carried so far as to stop respiration: in some
cases the patient has died before the first stage of insensibility.
These fatal cases have all been marked by a sudden paralysis of the
heart—that organ has abruptly ceased to act. Why in these, certainly a
very small percentage of patients, the action of the drug should at once
take effect on the heart has not yet been explained. The rhythmic action
of the heart depends upon nervous centres enclosed within its own
substance, so that this organ is to a certain extent independent; but it
is connected with the other nervous centres by the branches of a
remarkable nerve which proceeds from the _medulla oblongata_, and also
by another set of nerves which come from the chain of ganglia called the
_sympathetic nerve_. The nerve connecting the heart with the _medulla_
is a branch of that called the _pneumo-gastric_, and it is a
well-established fact that the action of the heart may be arrested by
irritation of this nerve. The comparatively few fatalities which have
attended the use of anæsthetics may, therefore, be due either to an
immediate action on the nerve-centres of the heart, or possibly to a
mediate action through the _medulla_ and the pneumo-gastric nerve.
Soon after the introduction of ether the use of nitrous oxide was
discontinued by the dentists, on account of the apparent uncertainty of
its action. Within the last few years, however, its employment in the
extraction of teeth has been revived by Dr. Evans, of Paris, who found
that to insure certainty in its action, the great point is the
inhalation of the gas in a pure state and without admixture of air.
Nitrous oxide seems now to be extensively used by dentists, and thus
Davy’s experiment of 1800 is repeated and verified daily in thousands of
cases, and to the great relief of hundreds who probably never heard his
name.
Other bodies, such as amylene (C_{5}H_{10}), carbon tetrachloride
(CCl_{4}), &c., have been tried as substitutes for ether and chloroform;
but having been found less efficacious or more dangerous, their use has
been abandoned. It might be instructive to reflect how much unnecessary
pain would have been spared to mankind had ether and chloroform been
known and applied at an earlier age. We know not what other beneficent
gifts chemistry may yet have in store for the alleviation of suffering,
but it is unlikely that even ether and chloroform are her _derniers
mots_. It should be remembered that the chemists who discovered and
examined these bodies were attracted to the work by nothing but the love
of their science. They had no idea how invaluable these substances would
afterwards prove. The chemist of the present day, whose labour is often
its own reward, may be cheered and stimulated in his toil by the thought
that while no discovery is ever lost, but goes to fill its appropriate
place in the great edifice of science, even the most apparently
insignificant truth may directly lead to invaluable results for humanity
at large.
What strange things the ancient thaumaturgists might have done had they
been possessed of the secret of chloroform or of nitrous oxide! What
miracles they would have wrought—what dogmas they would have sanctioned
by its aid! But the remarkable effects produced by the inhalation of
certain gases or vapours were not altogether unknown to the
ancients—although these effects were then attributed to anything but
their real cause. It is related that a number of goats feeding on Mount
Parnassus came near a place where there was a deep fissure in the earth,
and thereupon began to caper and frisk about in the most extraordinary
manner. The goatherd observing this, was tempted to look down into the
hole, to see what could have caused so extraordinary an effect. He was
himself immediately seized with a fit of delirium, and uttered wild and
extravagant words, which were supposed to be prophecies. The knowledge
of the presumed divine inspiration spread abroad, and at length a temple
in honour of Apollo was erected on the spot. Such was the origin of the
famous Oracle of Delphi, where the Pythoness, the priestess of Apollo,
seated on a tripod placed over the mysterious opening, delivered the
response of the god to such as came to consult the oracle. It is stated
by the ancient writers, that when she had inhaled the vapour, her eyes
sparkled, convulsive shudders ran through her frame, and then she
uttered with loud cries the words of the oracle, while the priests who
attended took down her incoherent expressions, and _set them in order_.
These possessions by the spirit of divination were sometimes violent.
Plutarch mentions a priestess whose frenzy was so furious, that the
priests and the inquirers alike fled terrified from the temple; and the
fit was so protracted that the unfortunate priestess herself died a few
days afterwards.
[Illustration:
FIG. 339.—_A Railway Cutting._
]
EXPLOSIVES.
The illustration above will serve to remind the reader of the great
importance of explosive agents in the operations of civil industry. By
reason of the more impressive and exciting spectacles which attend the
use of such agents in warfare, we are rather apt to lose sight of their
far more extensive utility as the giant forces whose aid man invokes
when he wishes to rend the rock in order to make a road for his steam
horse, or in order to penetrate into the bowels of the earth in search
of the precious ore. A little reflection will show that if such work had
to be done with only the pickaxe, the chisel, and the crowbar, the
progress would be painfully slow; and railway cuttings through masses of
compact limestone, like that represented in Fig. 339, for example, would
be well-nigh impossible. The formation of cuttings and tunnels, and the
removal of rocks in mining operations, are not the only service which
explosive agents render to the industrial arts; there is, besides other
uses which might be enumerated, the preparation of foundations for
buildings, bridges, harbours, and lighthouses. The use of gunpowder in
all such operations as those which have been referred to is too well
known to require description. But of late years gunpowder has been to a
great extent superseded for such purposes by two remarkable products of
modern chemistry, called _gun-cotton_ and _nitro-glycerine_. Military
art has also benefited by at least one of these products; and the use of
charges of gun-cotton for torpedoes has already been described and
illustrated in these pages.
It is not a little curious that the two most terribly powerful
explosives known to science should be prepared from two most harmless
and familiar substances. The nice, soft, clean, gentle cotton-wool, in
which ladies wrap their most delicate trinkets, becomes, by a simple
chemical transformation, a tremendously powerful explosive; and the
clear, sweet, bland liquid, glycerine, which they value as a cosmetic
for its emollient properties, becomes, by a like transformation, a still
more terrifically powerful explosive than the former. It is, perhaps,
even more curious that having undergone the transformation which confers
upon it these formidable qualities, neither cotton-wool nor glycerine is
changed in appearance. The former remains white and fleecy; the latter
is still a colourless syrupy-looking liquid.
The fibres which form cotton, linen, paper, and wood, are composed
almost entirely of a substance which is known to the chemist as
_cellulose_ or _cellulin_. That this substance, as it exists in the
fibres of linen and in sawdust, could be converted into an explosive
body by the action of nitric acid, appears to have been first observed
by the French chemist, Pelouze, in 1838. The action with cellulose in
the form of cotton-wool was more fully examined by Professor Schönbein,
of Basle, who, in 1846, first described the method of preparing
_gun-cotton_, and suggested some uses for it. He directs that one part
of finely-carded cotton-wool should be immersed in fifteen parts of a
mixture of equal measures of strong sulphuric and nitric acids; that
after the cotton has remained in the mixture for a few minutes, it
should be removed, plunged in cold water, and washed until every trace
of acid has been removed, and then carefully dried at a temperature not
exceeding the boiling-point of water.
After Professor Schönbein had demonstrated the power of the new agent in
blasting, and its projectile force in fire-arms, its manufacture on a
large scale was undertaken at several places. Messrs. Hall commenced to
make it at their gunpowder works at Faversham, and a manufactory was
also established near Paris. In July, 1847, a fearful explosion of
gun-cotton occurred at the Faversham works, which was believed to have
been caused by the spontaneous detonation of that substance. This
induced Messrs. Hall to discontinue the manufacture as too dangerous;
and they even destroyed a large quantity of the product which they had
in hand by burying it in the ground. The making of gun-cotton was soon
afterwards discontinued also by the French, who did not find the
substance to possess all the qualities fitting it for military use. The
Prussian Government also began to make gun-cotton; but the experiments
were put a stop to by the explosion of their factory. An eminent
artillery officer in the Austrian service, General von Lenk, undertook a
thorough examination of the manufacture and properties of gun-cotton for
military purposes. He introduced several improvements into the processes
of the manufacture; and the Austrian Government established works at
Hïrtenberg, with a view to the adoption of gun-cotton as a substitute
for gunpowder in fire-arms. It has some undoubted advantages over
powder, for it neither heats the gun nor fouls it, and it produces no
smoke. Notwithstanding this the Austrians have not abandoned the use of
gunpowder in favour of gun-cotton.
Gun-cotton, as a military agent, has a strenuous advocate in Professor
Abel, who presides over the Chemical Department of the British War
Office. To this gentleman we are indebted for great improvements in the
manufacture of gun-cotton, and for a more complete investigation of its
properties. Professor Abel’s processes were put in practice at a
manufactory which the Government established at Waltham Abbey; and
Messrs. Prentice also set up works at Stowmarket.
Some details of the mode in which the manufacture of gun-cotton was
carried on at Stowmarket may be of interest. The cotton was first
thoroughly cleansed and carefully dried; and these operations are of
great importance, for unless they are well performed, the product is
liable to explode spontaneously. The cotton was then weighed out in
charges of 1 lb., and each charge was completely immersed in a separate
vessel, containing a cold mixture of sulphuric and nitric acids. After a
short immersion the cotton was removed from the liquid, and with about
ten times its own weight of acids adhering to it, each charge was placed
in a separate jar, where it was allowed to remain for forty-eight hours.
The vessels were kept cool during the whole period by being placed in a
trough through which cold water was flowing. On removal from the jars,
the cotton was freed from adhering acid by being placed in a centrifugal
drying machine. It was then drenched with a large quantity of cold
water, and dried, washed again in a stream of cold water for forty-eight
hours, and the operations of alternately washing for forty-eight hours
and drying were repeated eight times. The drying was effected by placing
the material in cylinders of wire-gauze, which were whirled round by a
steam engine at the rate of 800 revolutions per minute, so that the
water was expelled by centrifugal force. The cotton was next reduced to
a pulp by a process similar to that which is employed in paper-making,
and the moist pulp was rammed into metallic cylinders by hydraulic
pressure, in order that it might be brought into forms suitable for use
in blasting, &c. The pulp was put into these moulds while wet, but the
water was nearly all expelled by the compression. The cylinders of
gun-cotton thus obtained were then covered with paper-parchment, and
finally dried at a steam temperature, with many precautions. The
compression of the cotton pulp, by bringing a large quantity of the
material into a smaller bulk, causes a greater concentration of the
explosive energy, and this is a matter of great importance in blasting.
We may now consider what chemistry has to teach concerning the nature of
the action by which cotton-wool is converted into gun-cotton. Cotton
itself is nearly pure cellulose. The chemical composition of cellulose
may be represented most simply by the formula C_{6}H_{10}O_{5}. Nitric
acid is a powerful oxidizing agent, and is constantly used in chemistry
to fix oxygen in various substances; but another kind of action exerted
by nitric acid in certain cases consists in the substitution of a
portion of its atoms for hydrogen, by which the residue of the particle
of nitric acid is converted into water. The formula for nitric acid may
be written HO NO_{2}, and it will be seen that by changing NO_{2} for H,
water, HOH, would be produced. This is precisely the kind of action
which occurs when cellulose is converted into _nitro-cellulose_. Two or
three, or more, atoms of hydrogen may be taken out of cellulose, and
replaced by two or three, or more, groups NO_{2}, and the result will be
a different kind of _nitro-cellulose_, according to the number of atoms
in the molecule replaced by NO_{2}. Several varieties of gun-cotton are
known, these being doubtless the result of the differences here alluded
to. The action producing di-nitro-cellulose is represented by this
equation:
C_{6}H_{10}O_{5} + 2HNO_{3} = C_{6}H_{8}(NO_{2})_{2}O_{5} + 2H_{2}O.
Cellulose. Nitric acid. Di-nitro-cellulose. Water.
The equation shows that water is produced by the reaction, and the
sulphuric acid which is used in the preparation performs no further part
than to take up this water, which would otherwise go to dilute the rest
of the nitric acid. The union of sulphuric acid and water is attended
with great heat, hence the necessity of cooling the vessels in making
the gun-cotton. Quite other products would be formed if the mixture
became heated.
The action of nitric acid on glycerine is of the same kind as that on
cellulose. When glycerine is allowed to drop into a cooled mixture of
nitric acid and sulphuric acid, the eye can detect little or no
difference between the appearance of the liquid which collects in the
bottom of the vessel and the glycerine dropped in. The product of the
action is, however, the terrible _nitro-glycerine_, a heavy,
oily-looking liquid, which explodes with fearful violence. Even a
single drop placed on a piece of paper, and struck on an anvil,
detonates violently and with a deafening report. The chemical change
which is effected in the glycerine (C_{3}H_{8}O_{3}), is the
substitution of three NO_{2} groups for three of hydrogen, producing
C_{3}H_{5}(NO_{2})_{3}O_{3}, or tri-nitro-glycerine. The general
reader may perhaps marvel that the chemist should be able not only to
count the number of atoms which go to make up the particles of a
compound body, but to say that they are arranged so and so: that the
atoms do not form an indiscriminate heap, but that they are connected
in an assignable manner. The reader is no doubt aware that these
compound particles are extremely small, and he may reasonably wonder
how science can pronounce upon the structure of things so small. He
may be more perplexed to learn that a calculation made by Sir W.
Thompson shows that the particles of water, for instance, cannot
possibly be more than the 1/250000000th of an inch in diameter, and
may be only 1/20th of that size. The truth is that the very existence
of atoms and molecules is an assumption. Like the undulatory ether, it
is an hypothesis which is adopted to simplify and connect our ideas,
and not a demonstrated reality. But the atomic hypothesis has so wide
a scope that some philosophers hold the existence of atoms and
molecules as almost a known fact. Be that as it may, the chemist in
assigning to a body a certain _molecular formula_ really does nothing
but express the results of certain experiments he has made upon it.
With one re-agent it is decomposed in this manner, with another in
that. By certain treatment it yields an acid, a salt; so much carbonic
acid, such a weight of water, is acted on or remains unaltered; gives
a precipitate or refuses to do so. Such are the _facts_ which the
chemist conceives are co-ordinated and expressed by the formula he
gives to a substance. The best formula is that which accords with the
greatest number of the properties of the body—which includes as many
of the facts as possible. It follows, therefore, that a formula which
aims at expressing more than the mere percentage composition of the
body—which, in the language of the atom hypothesis, seeks to represent
the mode in which the atoms are grouped in the molecule, but which in
reality represents only reactions, is written according as the chemist
considers this or that group of reactions more important. These
remarks might be illustrated by filling this page with the different
formulæ (a score or more) which have been proposed as representing the
constitution (_reactions?_) of one of the best-known of organic
compounds, namely, acetic acid.
Whether atoms really exist, and their arrangement in the particles of
bodies can be deduced from the phenomena, or not, the fact is undeniable
that these ideas have given chemists a wonderful grasp of the facts of
their science. The consistency and completeness of the explanation
afforded by these theories are ever being extended by modifications
which enable them to embrace more and more facts. Some of the properties
of the substance we are now considering confirm in a remarkable manner
the theoretical views which are expressed in its constitutional formula.
We may first consider the nature of gunpowder, and by comparing it with
nitro-glycerine, endeavour to explain the greater power of the latter
substance. Gunpowder is a mixture of charcoal, sulphur, and nitre, the
latter constituting three-fourths of its weight. Nitre supplies oxygen
for the combustion of the charcoal, which is thus converted into
carbonic acid, and the sulphur, which is added to increase the rapidity
of the combustion, is also oxidized. The products of the action are,
however, numerous and complicated, but the important result is the
sudden generation of a quantity of carbonic acid, nitrogen, carbonic
oxide, hydrogen, and other gases, which at the oxidizing temperature and
pressure of the air would occupy a space 300 times greater than the
powder from which they are set free; but the intense heat attending the
chemical action dilates the gases, so that at the moment of explosion
they would occupy a space at least 1,500 times greater than the
gunpowder. The materials of which gunpowder is composed are finely
powdered, in order that each portion shall be in immediate contact with
others, which shall act upon it. Plainly, the more thorough the
incorporation of the materials—that is, the more finely ground and
intimately mixed they are—the more rapid will be the inflammation of the
powder.
Looking now at the crude formula of nitro-glycerine,
C_{3}H_{5}N_{3}O_{9}, the reader will remark that the molecule contains
more than sufficient oxygen to form carbonic acid with all the carbon
atoms, and water with all the hydrogen atoms; for the C_{6} in _two_
molecules of nitro-glycerine would take only O_{12} to form 6CO_{2}; and
the H_{10}, to be converted into 5H_{2}O, would only need O_{5}; thus
there would be an excess of oxygen. Now, it may occur to the reflective
reader that in every molecule of nitro-glycerine the carbon and hydrogen
are already associated with as much oxygen as they can take up: that
they are, in fact, already burnt, and that no further union is possible.
But from chemical considerations it has been deduced that in the
nitro-glycerine molecule the oxygen atoms, except only three, which are
partially and _imperfectly_ joined to carbon, are united to nitrogen
atoms only. The constitution of the molecule may be represented by
arranging, as below, the letters which stand for the atoms, and by
joining them with lines, which shall stand for the bonds by which the
atoms are united.
O H H H O
| | | | |
N—O—C—C—C—O—N
| | | | |
O H O H O
|
O=N=O
We see here that the hydrogen atoms are completely, and the carbon atoms
partially, detached from the oxygen atoms; and therefore these atoms are
in the condition of the separated carbon and oxygen atoms in gunpowder.
Only the pieces of matter which lie side by side in gunpowder are in
size to the molecules of nitro-glycerine as mountains to grains of sand.
The mixture of the materials is then so much more intimate in
nitro-glycerine, since atoms which can rush together are actually within
the limits of the molecules; and these molecules have such a degree of
minuteness, that 25 millions, at least, could be placed in a row within
the length of an inch. We know that the finer the grains and the more
intimate the mixture, the quicker will gunpowder inflame; but here we
have a mixture far surpassing in minute subdivision anything we can
imagine as existing in gunpowder. Hence the combination in the case of
nitro-glycerine must be instantaneous, whereas that in gunpowder, quick
though it be, must still require a certain interval. If it take a
thousandth of a second for the gases to be completely liberated from a
mass of gunpowder, and only one-millionth of a second for a vast
quantity of carbonic acid, nitrogen, and steam to be set free from
nitro-glycerine, the destructive effect will be much greater in the
latter case. Again, the volume of the gases liberated from
nitro-glycerine in its detonation have at least 5,000 times the bulk of
the substance. We have entered into these chemical considerations, at
some risk of wearying the reader, with the desire of affording him a
clue to the singular properties of nitro-glycerine and gun-cotton, which
we are about to describe.