colour-producing substances found in coal-tar, we have not in the list
of coal-tar colours included the colouring matter which anthracene is
capable of yielding. The reason is that this case stands apart in some
respects from the rest. The colours derived from aniline and the other
substances already enumerated are instances of the production of bodies
not found in nature—mauve, magenta, &c., do not, so far as we know,
exist in nature. Their artificial formation was a production of
substances absolutely new. The colour of which we have now to treat is,
on the other hand, found in nature, and from its occurrence in the
_rubia tinctoria_, the roots of that plant have for ages been employed
as a source of colour, and are well known in this country as “madder.”
The plant is grown largely in Holland, in France, in the Levant, and in
the south of Russia.[18] Madder is used in enormous quantities for
dyeing reds and purples: the well-known “Turkey red” is due to the
colouring matter of this root. The total annual value of the madder
grown is calculated to reach nearly 2½ million pounds sterling. More
than forty years ago it was discovered that the madder-root yielded a
colouring substance, to which the name of “alizarine” was bestowed, from
_alizari_, the commercial designation of madder in the Levant. The
alizarine does not exist in the fresh root, but is produced in the
ordinary processes of preparing the root and dyeing with it, in
consequence of a peculiar decomposition or fermentation. Alizarine may
be procured from dried madder by simply submitting it to sublimation,
when beautiful orange needle-shaped crystals of alizarine may be
obtained. It is nearly insoluble in water, but readily dissolves in hot
spirits of wine. Acids do not dissolve it, but potash dissolves it
freely, striking a beautiful colour; with lime, barytes, and oxide of
iron, it forms purple lake, and with alumina a beautiful red lake.
According to Dr. Schunck, of Manchester, to whose investigations we are
indebted for much of our knowledge of madder, the root contains a bitter
uncrystallizable substance called “rubian,” which, under the action of
certain ferments, and of acids and alkalies, is decomposed into a kind
of sugar, and into alizarine and other colouring matters. The ferment,
which in the process of extracting the colouring matter from the roots
causes the formation of alizarine, is contained in the root itself.
Footnote 18:
The natural Order to which the madder plant belongs is interesting
from the number of its members which supply us with useful products.
That valuable medicine, quinine, is obtained from plants belonging to
this family, as is also ipecacuanha, and other articles of the
_materia medica_. _Coffea arabica_, which furnishes the coffee-berry,
is another member.
We have already seen how an investigation relating to a question of pure
chemical science accidentally led Mr. Perkin to the discovery of
mauve—the precursor of the long range of beautiful colours already
described. The mode of artificially preparing alizarine, so far from
being an accidental discovery, was sought for and found in 1869 by two
German chemists, Graebe and Liebermann. The researches of these chemists
were conducted in a highly scientific spirit. Instead of making attempts
to produce alizarine by trying various processes on first one body, then
another, to see if they could hit upon some tar product, or other
substance, which would yield the desired product, they began by
operating analytically on alizarine itself. Just as a mechanic ignorant
of horology, required to make a watch, would be more likely quickly to
succeed in his task by taking a watch to pieces to see how it is put
together, than if he had tried all manner of arranging springs and
wheels until he hit upon the right way; so these chemists set themselves
to take alizarine to pieces, in order to see from what materials they
might be able to put it together. They decomposed alizarine, and among
the products found a hydro-carbon identical in all its properties with
_anthracene_.
Anthracene was discovered in coal-tar by Laurent in 1832, and its
properties were investigated by Anderson in 1862. It may be remarked
that such investigations were not conducted with a view to any
industrial uses of anthracene, but merely for the sake of chemistry as a
science. Certainly no one could have supposed at that time that the
slightest relation existed between anthracene and madder. Anthracene is
a white solid hydro-carbon, which comes over only in the last stages of
the distillation of coal-tar, accompanied by naphthaline, from which it
is easily separated by means of spirits of wine, by which the
naphthaline is readily dissolved, but the anthracene scarcely. Anderson,
in 1861, discovered, among other results, that anthracene, C_{14}H_{10},
by treatment with nitric acid became changed into oxy-anthracene,
C_{14}H_{8}O_{2}; and this reaction we shall see is a step in the
process of procuring alizarine from anthracene. Phenol, as already
mentioned, can be made to yield benzol, by a process of deoxidization.
With a view to similarly obtaining a hydro-carbon from alizarine, Graebe
and Liebermann passed its vapours over heated zinc filings, and thus
produced anthracene from alizarine. It now remained to find a means of
reversing this process, that is, so to act on anthracene as to produce
alizarine, and this was effected by treating anthracene with bromine,
forming a substance which, on fusing with caustic potash, yielded
_alizarate of potash_, from which pure alizarine resulted by treatment
with hydrochloric acid. A much cheaper method was, however, necessary
for manufacturing purposes, and it was found in a process by which
oxy-anthracene, C_{14}O_{8}H_{2}, is treated at a high temperature with
strong sulphuric acid, and the product so formed heated with a strong
solution of potash, yielding alizarate of potassium as before. Many
other interesting substances appear to be formed in the reactions, but
the nature of these bodies has as yet been imperfectly investigated. No
doubt whatever can be entertained of the identity of natural with
artificial alizarine; and the production of this substance, the first
instance of a natural colouring matter made artificially, may be
regarded as a great triumph of chemical science. It was not long ago
supposed that the chemical bodies found in plants or animals, or
produced by vital actions, could not possibly be formed by any
artificial process from their elements. The laws which presided at their
formation were, it was conceived, wholly different from those which
governed the chemicals of the laboratory, for they were held to act
exclusively under the influence of a mysterious agent, namely, “vital
force.” It was supposed, for example, that from pure carbon, oxygen, and
hydrogen, no chemist would ever be able to produce such a compound as
acetic acid. Accordingly the domain of chemical science, previous to the
end of the first quarter of the present century, was divided by an
impassable barrier into the two regions of organic and inorganic
chemistry. Now, however, the chemist is able to build up in his
laboratory from their very elements a great number of the so-called
_organic_ bodies. And it is quite possible to do this in the case of
alizarine; that is, a chemist having in his laboratory the elements,
hydrogen, carbon, oxygen, &c., could actually build up the substance
which gives its value to madder.
The quantity of anthracene procurable from coal-tar is, unfortunately,
comparatively small, for it is found that from the distillation of 2,000
tons of coal only one ton of anthracene can be obtained. The use of
artificial alizarine would doubtless entirely supplant the employment of
madder-root if anthracene could be obtained in larger quantities; and
the change would be highly advantageous to this country, for as no
madder is grown in Great Britain, and we consume nearly half the whole
annual growth, it follows that every year a million pounds sterling go
out of the country for this commodity. When anthracene is produced from
coal in sufficient abundance, this sum will be available for the support
of our own population. In the meantime, the manufacture of artificial
alizarine is restricted only by the supply of its raw material.
The foregoing paragraphs of the present article, which were written for
the first edition of this work, not long after the introduction of
artificial alizarine, require some supplementary reference to the
subsequent progress of discovery and to the increased importance of the
manufacture of the coal-tar colours on the large scale. Since the first
introduction of alizarine as a commercial product, the substance has
received much attention from chemists. The constitution of the body
called above _oxy-anthracene_ is now better understood, and its chemical
relationship is more clearly indicated by the systematic name of
_anthraquinone_, which it now bears. The process of the manufacture of
alizarine has received some advantageous modifications, and the
artificial product may now be said to have entirely displaced the
madder-root in dyeing. But, more than this, chemists have found means of
preparing a number of “derivatives” of alizarine, many of which are
either colouring matters or are easily converted into such. Nearly
thirty of these substances have been described, and several of them have
found extensive industrial applications. We may mention _alizarine
blue_, C_{17} H_{9} NO_{4}, and another substance, produced by combining
that with _sodium bi-sulphite_, and having the formula C_{17} H_{9}
NO_{4} 2Na H SO_{3}. This last, manufactured largely, and sold under the
name of “_alizarine blue S._,” is remarkable for being one of the most
permanent of all colouring matters. It is said to be a faster colour
than even indigo blue, which, indeed, it is rapidly replacing in dyeing,
where it is applicable to cotton with a chromium mordant and to silk
with one of alumina. Two other colouring matters have also been derived
from anthracene, and are much used in dyeing; one is commercially named
_anthracene purple_, the other is _anthracene green_, which supplies the
calico printer with very fast shades of olive-green.
Several of the substances enumerated in the list of coal-tar colours, in
pages 689 and 690, are now but little used, or altogether abandoned in
dyeing and calico printing, because either their beautiful hues prove
too fugitive, or other bodies of the same class can be produced at a
much cheaper rate. The range of choice is now of the amplest, for
chemical discovery has been wonderfully active, but in many cases the
real nature and relationship of the artificial colouring matters
enumerated above have only quite recently been made out. Mauve (now
called _rosaline_), for example, the oldest of all the colour-tar
colours, and one which, as we have seen, was manufactured on an
extensive scale many years ago, is now scarcely made at all, because
much cheaper violets have taken its place. The science of the tinctorial
substances has lately taken a much more distinct form, and this
knowledge has borne fruit for industrial purposes. It would be out of
place here to review what has been done in this way, but a few facts
will show the richness of the field. It was only in 1886 that the true
chemical constitution of a class of coal-tar derivatives, called
_azines_, was first made out. They present themselves as pale yellow or
orange coloured crystallized solids, which melt at a comparatively high
temperature and may be distilled without decomposition. Although highly
coloured substances themselves, before they are converted into fast dyes
they require further treatment, which introduces into their molecules
another group of atoms. An almost indefinite number of such compounds
are theoretically possible, but from only a very few of them many useful
dye stuffs are now prepared on the large scale. Amongst the most
important of these are “neutral red,” “neutral violet,” and two other
violet colouring matters, “red dyestuff,” “fuchsia,” “giroflé,” “Magdala
red,” “indazine” and “Basle blue.”
Among the colouring matters before enumerated are “aniline yellow” and
“Bismarck brown.” Their real nature was not understood until a few years
ago; and though the use of the aniline yellow itself has been abandoned
on account of its fugacity, the substance has been found a most prolific
parent, which has supplied dye stuffs of the most diverse and brilliant
hues. These form what chemists term the _azo colours_, and they have
been manufactured in great variety and on a very large scale. In 1876,
the class of them called _chrysoidines_ was introduced, and again, in
1878, _tropœolines_. Great numbers of different azo colours have been
sent into commerce under various names, such as “butter yellow,”
“_crocein scarlet_,” “_Biebrich scarlet_,” “_Congo red_,” “_Bordeaux
G._,” “fast red,” &c., &c. About 140 of these azo dyes have been
described, and the commercial importance of this one class of compounds
alone may be inferred from the fact of no fewer than 200 patents having
been taken out for processes relating to their manufacture in the eleven
years from 1878 to 1888.
It would not be difficult to fill this book with instances of the way in
which the resources of modern life have been increased by chemistry
alone, a science almost entirely the creation of the present century.
Many of the processes of manufacture in which chemistry is applied to
the production of articles of every-day use have been so often
described, that they may be assumed to be already so well known as to
offer few elements of novelty to the general reader, whose interest
would also be likely to flag if he were carried over a long range of
even the brilliant discoveries that are so delightful and instructive
for the special students of this science. There is no parallel to the
rapidity of the progress made by the younger branch of the science which
concerns itself with the chemistry of one element—namely, carbon and its
various combinations, and it is from these carbon compounds that our
examples have been drawn. In the explosives, we have some of these
compounds supplying resistless forces for rending rocks, and furnishing
in warfare the most dreadful powers of destruction. In anæsthetics, we
see beneficent applications of others in alleviating suffering and
annulling pain; and again we have just shown how richly another set of
them can minister to our sense of beauty. The discussion of these topics
has afforded an opportunity for bringing before the reader some of the
laws or summarized statements of experimental facts, and also some of
those symbolical conceptions of the constitution of compounds, which
together furnish the clues that guide the chemist through the vast
labyrinth of the endless transformations of matter. The results attained
show that the notions expressed by such words as _atom_, _molecule_,
_compound radical_, _structural formula_, etc., have a true
representative correspondence with something in the actual constitution
of bodies.
[Illustration:
FIG. 357.—_James Prescott Joule, F.R.S._
]
THE GREATEST DISCOVERY OF THE AGE.
The indulgent reader who may have followed the course of the foregoing
pages, will perhaps peruse the title of this article with some little
bewilderment. His attention has been drawn to one after another of a
series of remarkable and important discoveries, and he will naturally
wonder what can be the discovery which is greater than any of these.
Now, a discovery is great in proportion to the extent and importance of
the results that flow from it. These results may be immediate and
practical, as in the case of vaccination; or they may be scientific and
intellectual, as in Newton’s discovery of the identity of the force
which draws a stone to the ground with that which holds the planets in
their orbits. Such discoveries as most enlarge our knowledge of the
world in which we live, by embracing in simple laws a vast field of
phenomena, are precisely those which are most prolific in useful
applications. If we admit, as we must, the truth of Bacon’s aphorism,
which declares that “Man, as the minister and interpreter of nature, is
limited in act and understanding by his observation of the order of
nature; neither his understanding nor his power extends farther,”[19]
then it would be easy to show that the discovery of which we have to
treat, more than any other, must be of immense practical service to
mankind in every one of the ways in which a knowledge of the order of
nature can be of use, viz.:—“First, In showing in how to avoid
attempting impossibilities. Second, In securing us from important
mistakes in attempting what is, in itself, possible, by means either
inadequate or actually opposed to the end in view. Third, In enabling us
to accomplish our ends in the easiest, shortest, most economical, and
most effectual manner. Fourth, In inducing us to attempt, and enabling
us to accomplish, objects which, but for such knowledge, we should never
have thought of undertaking.”[20]
Footnote 19:
“Homo naturæ minister et interpres, tantum facit et intelligit quantum
de naturæ ordine re vel mente observaverit: nec amplius scit aut
potest.”—_Novum Organum, Aphor._ I.
Footnote 20:
Sir J. Herschel.
A great principle, like that which we are about to explain to the
reader, is too vast in its bearings for its discovery and elaboration to
have been the work of an individual. This truth, and indeed the whole of
our knowledge, is but the result of the development and growth of
pre-existing knowledge. In fact, every discovery, however
brilliant—every invention, however ingenious, is but the expansion or
improvement of an antecedent discovery or invention. In strictness,
therefore, it is impossible to say where the first germ of even our
newest notions may be found. Our latest philosophy can be shown to be
the result of progressive modifications of ideas of remote ages. Hence
every great truth, every grand invention, has in reality been the
offspring of many minds; but we record as _the_ discoverers and
inventors those men who have made the longest strides in the path of
progress, and whose genius and labours have overcome obstacles defying
ordinary efforts.
The extent of the field which is covered by the principle we have in
view is so vast—embracing, as it does, the whole phenomena of the
universe—that it will not be possible to do more within our limits than
give the reader a general notion of the principle itself. It may be
useful to instance a truth which has a similar generality and
significance, and which has also acquired the force of an axiom, because
it is verified every hour. It is that greatest generalization of
chemistry, affirming that in all its transformations _matter is
indestructible_, and can no more be destroyed than it can be called into
being at will. This truth is so well established, that some philosophers
have asserted that an opposite state of things is _inconceivable_. But
it was not always known; and there are at the present day untutored
minds which not only believe that a substance destroyed by fire is
utterly annihilated, but what they find _inconceivable_ is the continued
existence of the substance in an invisible form. The candle burns away,
its matter vanishes from our view; but if we collect the invisible
products of the combustion, we find in them the whole substance of the
candle in union with the atmospheric oxygen. We may, in imagination,
follow the indestructible atoms of carbon in their migrations, from the
atmosphere to the plant, which is eaten by the animal and goes to form
its fat, and from the tallow, by combustion, back into the atmosphere
again. The notion of the real identity of matter under changing forms
has been expressed by our great dramatist in a well-known passage, which
is remarkable for its philosophic insight, when we consider the age in
which it was written:
HAMLET. To what base uses we may return, Horatio! Why may not
imagination trace the noble dust of Alexander, till he find it
stopping a bung-hole?
HORATIO. ‘Twere to consider too curiously to consider so.
HAMLET. No, faith, not a jot; but to follow him thither with
modesty enough, and likelihood to lead it. As thus: Alexander
died, Alexander was buried, Alexander returneth to dust; the dust
is earth; of earth we make loam; and why of that loam, whereto he
was converted, might they not stop a beer-barrel?
Imperial Cæsar, dead, and turned to clay,
Might stop a hole to keep the wind away;
O, that the earth, which kept the world in awe,
Should patch a wall to expel the winter’s flaw!
Now the greatest discovery of our age is that force, like matter, is
indestructible, and that it can no more be created than can matter. The
reader may perhaps think the statement that we cannot create force is in
contradiction to experience. He will be disposed to ask, What is the
steam engine for but to create force? Do we not gain force by the
pulley, the lever, the hydraulic press? And are not tremendous forces
produced when we explode gunpowder or nitro-glycerine? When the
principle with which we are here concerned has been developed and stated
in accurate terms, it is hoped the reader will see the real nature of
these contrivances. We are, however, aware that it is quite impossible
within the limits of a short article to do much more than indicate a
region of discovery abounding with results which may be yet unfamiliar
to some. Into this, if so minded, they should seek for further guidance,
which they will pleasantly find in the pages of Dr. Tyndall’s “Heat
considered as a Mode of Motion,” and in a little work by Professor
Balfour Stewart, entitled “The Conservation of Energy,” and quite
fascinating from the clearness and simplicity of its style. We may
continue our humble task of merely illustrating the general nature of
this, in reality the most important, subject which we have had occasion
to bring under the reader’s notice.
Perhaps the first step should be to point out the fact of the various
forces of nature—mechanical action, heat, light, electricity, magnetism,
chemical action—being so related that any one can be made to produce all
the rest directly or indirectly. Some examples of the conversion of one
form of force into another occur in the foregoing pages. Thus, on page
485 an experiment is described in which electricity produces a
mechanical action; electricity is also shown, on page 496, to produce
heat; on page 491 chemical action; on page 501 magnetism. Then, as
instances of the inverse actions, there is on page 488, in the first
paragraph on “Electric Induction,” an account of the mode in which
mechanical movements may give rise to electricity; and in the
experiments in pages 508, 509, and particularly in the account of the
Gramme machine, page 511, it is shown how mechanical movements can,
through magnetism, produce electricity. The voltaic element, page 491,
and the galvanic batteries, are instances of chemical action supplying
electricity. On page 518 a striking instance is mentioned of changes in
the forms of force. Every lighted candle is a case of chemical action
giving rise to light; and interesting examples of the inverse relation
are referred to on page 608. On page 168 is represented the conversion
of arrested motion into heat and light. We have, indeed, sufficient
examples to arrange a series of these conversions of forces in a circle.
Thus, chemical action (oxidation in the animal system) supplies muscular
power, this sets in motion a Gramme machine, the motion is converted
into electricity, the electricity produces the electric light, and light
causes chemical action, and with this the cycle is complete. In the
steam engine heat is converted into mechanical force, and many cases
will present themselves to the reader’s mind in which mechanical actions
give rise to heat. The doctrine of a mutual dependence and
convertibility among all the forms of force was first definitively
taught in England by Mr. (now Justice) Grove, in 1842; and almost
simultaneously Dr. Meyer promulgated similar views in Germany. Mr. Grove
subsequently embodied his doctrine in a treatise, called “The
Correlation of the Physical Forces,” which has seen several editions.
But this teaching included much more than a mere connection between the
various forces, for it extended to quantitative relations. It declared
that a given amount of one force always produced a definite amount of
another, that a certain quantity of heat, for example, would give rise
to a certain amount of mechanical action, and that this amount of
mechanical action was the _equivalent of the heat_ which produced it,
and would in its turn reproduce all that heat. These last doctrines,
however, rested on a speculative basis, until Mr. James Prescott Joule,
of Manchester, carried out a most patient, laborious, and elaborate
experimental investigation of the subject. His labours placed the truth
of the numerical equivalence of forces on a foundation which cannot be
shaken; and he accomplished for the principle of the indestructibility
of force what Lavoisier did for that of the indestructibility of
matter—he established it on the incontrovertible basis of accurate and
conclusive experiment. His determination of the value of the _mechanical
equivalent of heat_ especially is a model of experimental research; and
subsequent investigators have, by diversified methods, confirmed the
accuracy of his results. A great part of his work consisted in finding
what quantity of heat would be produced by a given quantity of _work_.