CHEMICAL FORCES.
Nature’s Chemistry--Changes produced by Chemical Combination--Atomic
Constitution of Bodies--Laws of Combination--Combining
Equivalents--Elective Affinity--Chemical Decomposition--Compound
Character of Chemical Phenomena--Catalysis or action
of Presence--Transformation of Organic Bodies--Organic
Chemistry--Constancy of Combining Proportions--The Law of Volumes,
the Law of Substitutions, Isomeric States, &c.
All things on the earth are the result of chemical combination. The
operations by which the commingling of molecules and the interchange
of atoms take place, we can imitate in our laboratories; but in nature
they proceed by slow degrees, and, in general, in our hands they are
distinguished by suddenness of action. In nature chemical power is
distributed over a long period of time, and the process of change is
scarcely to be observed. By art we concentrate chemical force, and
expend it in producing a change which occupies but a few hours at most.
Many of the more striking phenomena of nature are still mysterious to
us, and principally because we do not, or cannot, take the element time
into calculation. The geologist is compelled to do this to explain the
progress of the formation of the crust of the earth, but the chemist
rarely regards the effects of time in any of his operations. The
chemical change which within the fissure of the rock is slowly and
silently at work, displacing one element or molecule, and replacing it
by another, is in all probability the operation of a truly geological
period. Many, however, of the changes which are constantly going on
around us, are of a much more rapid character, and in these nature is
no slower in manipulating than the chemist.
Had it been that the elements which are now found in combination
could exist in a free state, the most disastrous consequences would
necessarily ensue. There must have been a period when many of the
combinations known to us were not yet created. Their elements either
existed in other forms, or were uncombined. Our rocks are compounds of
oxygen with certain peculiar metals which unite with oxygen so rapidly
that incandescence is produced by their combination. Let us suppose
that any of these metals existed in purity, and that they were suddenly
brought into contact with water, the atmospheric air, or any body
containing oxygen, the result would be a convulsion of the most fearful
kind; the entire mass of metal would glow with intensity of heat, and
the impetuosity of the action would only be subdued when the whole
of the metal had become oxidized. Volcanic action has been referred
to some such cause as this, but there is not sufficient evidence to
support the hypothesis; indeed, it is contrary to the opinion of most
philosophers.[200] Such a condition may possibly have existed at one
time, during that period when darkness was upon the face of the deep,
when the earth was a chaos; but it is only adduced here as an example
of the violent nature of some chemical changes. Potassium thrown on
water bursts into flame, and sodium does so under certain conditions.
If these, or the metals proper in a state of fine division, are brought
into an atmosphere of chlorine, the intensity of chemical action is so
great that they become incandescent, many of them glowing with extreme
brilliancy. If hydrogen gas is mixed with this element (chlorine)
they unite, under the influence of light, with explosive violence,
giving rise to a compound, muriatic acid, which combines with water
in an almost equally energetic manner. Nitrogen, as it exists in the
atmosphere, mixed with oxygen, appears nearly inert; with hydrogen it
forms the pungent compound, ammonia; with carbon, the poisonous one,
cyanogen, the base of prussic acid; with chlorine it gives rise to a
fluid, oily in its appearance, but which, when merely touched by an
unctuous body, explodes more violently than any other known compound,
shivering whatever vessel it may be contained in, to atoms; with iodine
it is only slightly less violent; and in certain combinations with
silver, mercury, gold, or platinum, it produces fulminating compounds
of the most dangerous character.[201] Here we have elements harmless
when uncombined, exhibiting the most destructive effects if their
combinations are at all disturbed; and in the other case we have inert
masses produced from active and injurious agents.
We regard a certain number of substances as _elementary_; that is to
say, not being able, in the present state of our knowledge, to reduce
them to any more simple condition, they are considered as the elements
which by combination produce the variety of substances found in the
three kingdoms of nature.
We have already spoken of the atomic constitution of bodies. It remains
now to explain the simplicity and beauty which mark every variety of
combination under chemical force. As a prominent and striking example,
water is a compound of two gaseous bodies, oxygen and hydrogen:--
If we decompose water by means of galvanic electricity, or determine
its composition by direct chemical analysis, we shall find it consists
of two volumes of hydrogen gas, united to one volume of oxygen, or, by
weight, of one part of hydrogen combined with eight of oxygen. In 100
parts, therefore, we should find--
Oxygen 88·9
Hydrogen 11·0
It is found in the same way that the theoretical weight of the atom
of carbon is 6, and that of nitrogen 14; whilst the atom of iron is
28, that of silver 108, of gold 199, and that of platinum and iridium
each 98.[202] Now, as these are the relative weights of the ultimate
indivisible atom, it follows that all combinations must be either atom
to atom, or one to two, three, or four; but that in no case should
combination take place in any other than a multiple proportion of the
equivalent or atomic number. This is found to be the case. Oxygen,
for instance, combines as one, two, or three atoms; its combination
presenting some multiple of its equivalent number 8, as 16, or 24:
and in like manner the combining quantity of carbon is 6, or some
multiple of that number. Where this law is not found strictly to agree
with analytical results, of which some examples are afforded by the
sesquioxides, it may be attributed, without doubt, to some error of
analysis or in the method of calculation.
Nothing can be more perfect than the manner in which nature regulates
the order of combination. We have no uncertain arrangement; but,
however great the number of the atoms of one element may be, over those
of another, those only combine which are required, according to this
great natural law, to form the compound, all the others still remaining
free and uncombined. These results certainly appear to prove that the
elementary particles of matter are not of the same specific gravities.
Do they not also indicate that any alteration in the specific gravity
of the atom would give rise to a new series of compounds, thus
apparently producing a new element? Surely there is nothing irrational
in the idea that the influences of heat or electricity, or of other
powers of which as yet we know nothing, may be sufficient to effect
such changes in the atomic constituents of this earth.
The combination of elementary atoms takes place under the influence
of an unknown force which we are compelled to express by a figurative
term, _affinity_. In some cases it would appear that the disposition
of two bodies to unite, is determined by the electrical condition; but
a closer examination of the question than it is possible to enter into
in this place, clearly shows that some physical state, not electrical,
influences combining power.
Chemical affinity or attraction is the peculiar disposition which one
body has to unite with another. To give some instances in illustration.
Water and spirit combine most readily: they have a strong affinity for
each other. Water and oil repel each other: they have no affinity;
they will not enter into combination. If carbonate of potash is added
to the spirit and water in sufficient quantity, the water is entirely
separated, and the pure spirit will float over the hydrated potash. If
potash is added to the oil and water, it combines with the oil, and,
forming soap, they all unite together; but, if we now add a little acid
to the mixture, the potash will quit the oil to combine with the acid,
and the oil will be repelled as before and float on the liquid. This
has been called single elective affinity. These elections were regarded
as constant, and chemists drew up tables for the purpose of showing the
order in which these decompositions occur.[203] Thus, ammonia, it was
shown, would separate sulphuric acid from magnesia, lime remove it from
ammonia, potash or soda from lime, and barytes from potash or soda. It
was thought the inverse of this order would not take place, but recent
researches have shown that the results are modified by quantity and
some other conditions.
It often happens that we have a compound action of this kind in which
double election is indicated. Sulphate of lime and carbonate of ammonia
in solution are brought together, and there result a carbonate of lime
and a sulphate of ammonia. Now, in such cases nothing more than single
elective attraction most probably occurs, and the carbonic acid is
seized by the lime, by the great affinity of that earth for carbonic
acid, only after it has been set free from the ammonia, and then, by
the force of cohesion acting with the combining powers, the insoluble
salt is precipitated.[204] There is a curious fact in connection with
this decomposition. If carbonate of lime and sulphate of ammonia
are mixed together dry, and exposed, in a closed vessel, to a red
heat, sulphate of lime and carbonate of ammonia are formed. These
opposite effects are not very easily explained. The action of heat is
to set free the carbonic acid; and it can only be by supposing that
considerable differences of temperature reverse the laws of affinity,
that we can at all understand this phenomenon. That different effects
result at high temperatures from those which prevail at low ones,
recent experiments prove to us, particularly those of Boutigny, already
quoted when considering decomposition by calorific action.
Under the term chemical affinity, which we regard as a power acting
at insensible distances, and producing a change in bodies, we are
content to allow ourselves to believe that we have explained the
great operations of nature. We find that the vegetable and animal
kingdoms are composed of carbon, hydrogen, oxygen, and nitrogen. The
granite mountains of the earth, and its limestone hills, and all its
other geological formations, are found to be metals and oxygen, and
carbon and sulphur, disposed to settle in harmonious union in their
proper places by chemical affinity. But what really is the power which
combines atom to atom, and unites molecule to molecule? Can we refer
the process to heat? The influence of caloric, although by changing
the form of bodies it sometimes assists combination, is to be regarded
rather as in antagonism to the power of cohesion. Can it be thought
that electricity is active in producing the result? During every change
of state, those phenomena which we term electrical are manifested; but
we thereby only prove the general diffusion of the electric principle,
and by no means show that electricity is the cause of the chemical
change. Can light determine these changes? It is evident, although
light may be a disturbing power, that it cannot be the effective one;
for many of these decompositions and recompositions are constantly
going on within the dark and silent depths of the earth, to which a
sunbeam cannot reach. That the excitation on the surface of the earth,
produced by solar influence, may modify those changes, is probable. It
is, however, certain that we must regard all manifestations of chemical
force as dependent upon some secret principles common to all matter,
diffused throughout the universe, but modified by the influences of the
known imponderable elements, and by the mechanical force of aggregative
attraction.
Bodies undergo remarkable changes of form, and present very different
characters, by reactions, which are of several kinds. We suppose
that a permanent corpuscular arrangement is maintained so long as
the equilibrium of the molecular forces is undisturbed. Water, for
instance, remains unchanged so long as the balance of affinity is kept
up between the oxygen and hydrogen of which it is composed, or so long
as the oscillations of force between these combining elements are
equal; but disturb this force, or set up a new vibratory action, as by
passing an electric current through the water, or by presenting another
body, which has the power of reacting upon one of these corpuscular
systems, and the water is decomposed, the hydrogen and oxygen gases
being set free, or one alone is liberated, and the other combined with
the molecules of the agent employed, and a new compound produced. This
is chemistry, by which science we discover all the combinations of
matter.
Having reason to conclude that atom combines with atom, according to
a system most harmoniously arranged, there can be no difficulty in
conceiving that molecule unites with molecule, in a manner regulated
by some equally well-marked law. It was, indeed, a discovery by
Wenzel, of Fribourg, that, in salts which decompose each other, the
acid which saturates one base will also saturate the other base;
and the subsequent observations of Richter, of Berlin, who attached
proportional numbers to the acids and bases, and who remarked that the
neutrality of metallic salts does not change during the precipitation
of metals by each other, which led the way to the atomic theory of Dr.
Dalton, to whom entirely belongs the observation, that the equivalent
of a compound body is the sum of the equivalents of its constituents,
and the discovery of combination in multiple proportions.
The elements of a molecule can take a new arrangement amongst
themselves, without any alteration in the number of the atoms or of
their weight, and thus give rise to a body of a different form and
colour, although possessing the same chemical constitution. This is the
case with many of the organic compounds of carbon and hydrogen.
The elements of a compound may be disassociated, and thus the
dissimilar substances of which it is composed set free. A piece
of chalk exposed to heat is, by the disturbance of its molecular
arrangement, changed in its nature; a gaseous body, carbonic acid,
is liberated, and quick-lime (oxide of calcium) is left behind. If
this carbonic acid is passed through red-hot metal tubes, or brought
in contact with heated potassium, it is resolved into oxygen and
charcoal--the oxygen combining with the metal employed. The oxide of
calcium (lime), if subjected to the action of a powerful galvanic
current, is converted into oxygen and a metal, calcium. Thus we learn
that chalk is a body consisting of two compound molecules,--carbonic
acid, which is formed by the combination of an atom of carbon with two
atoms of oxygen,--and lime, which results from the union of an atom of
calcium with one of oxygen.
The condition requisite to the production of chemical action between
bodies is that they should be dissimilar. Two elementary atoms
are placed within the spheres of each other’s influences, and a
compound molecule results. Oxygen and hydrogen form water; oxygen
and carbon give rise to carbonic acid; nitrogen and hydrogen unite
to form ammonia; and chlorine and hydrogen to produce hydrochloric
acid. In all these cases an external force is required to bring the
atoms within the range of mutual affinity: flame,--the electrical
spark,--actinism,--or the interposition of a third body, is necessary
in each case. There are other examples in which no such influence is
required. Potassium and oxygen instantly unite: chlorine, iodine, and
bromine immediately, and with much violence, combine with the metals to
form chlorides, iodides, or bromides.
With compound molecules the action is in many cases equally active,
and combination is readily effected, as in the cases of the acids and
the oxides of some metals, which are all instances of the most common
chemical attraction.
An elementary or simple molecule and molecules of a compound and
different constitution are brought together, and a new compound
results from an interchange of their atoms, whilst an element is
liberated. These are essentially illustrations of analytical chemistry.
Sulphuretted hydrogen is mixed with chlorine; the chlorine combines
with the hydrogen, and sulphur is set free. Potassium is put into
water, and it combines with the oxygen of the water, whilst the
hydrogen is liberated.
Two compound molecules being brought together may decompose each other,
and form two new compounds by an interchange of their elements.
One element may be substituted for another under certain circumstances.
Gold may be replaced by mercury; copper will take the place of silver;
and iron will occasion the separation of copper from its solutions,
the iron itself being dissolved to supply its place; chlorine will
substitute hydrogen in the carburetted hydrogen gases; and many other
examples might be adduced.
Chemical phenomena very frequently become of a complex character;
and one, two, or three of these cases may be occurring at the same
time in the decomposition of one compound by another. Such are the
general features of chemical science. Many peculiarities and remarkable
phenomena connected with chemical investigations will be named, as
the examination of the elementary composition of matter is proceeded
with; but, although the philosophy of chemical action is of the highest
interest, it must not be allowed to detain us with its details, which
are, indeed, more in accordance with a treatise on the science than
one which professes to do no more than sketch out those prevailing
and striking features which, whilst they elucidate the great truths
of nature, are capable of being employed as suggestive examples of
the tendency of scientific investigation to enlarge the boundaries of
thought, and give a greater elevation to the mind, leading us from
the merely mechanical process of analysis up to the great synthetical
operations, by which all that is found upon the earth for its ornament,
or our necessities, is created.
Among the most remarkable phenomena within the range of physical
chemistry are those of _Catalysis_, or, as it has also been called, the
“_Action of presence_.”[205] There are a certain number of bodies known
to possess the power of resolving compounds into new forms, without
undergoing any change themselves. Kirchoff discovered that the presence
of an acid, at a certain temperature, converted starch into sugar and
gum, no combination with the acid taking place. Thenard found that
manganese, platinum, gold, and silver, and, indeed, almost any solid
organic body, had the power of decomposing the binoxide of hydrogen by
their presence merely, no action being detected on these bodies. Edmund
Davy found that powdered platinum, moistened with alcohol, became
red-hot, fired the spirit, and converted it into vinegar, without
undergoing, itself, any chemical change. Döbereiner next discovered
that spongy platinum fired a current of hydrogen gas directed upon
it, which, by combining with the oxygen of the air, formed water.
Dulong and Thenard traced the same property, differing only in degree,
through iridium, osmium, palladium, gold, silver, and even glass.
Further investigation has extended the number of instances; and it has
even been found that a polished plate of platinum has the power of
condensing hydrogen and oxygen so forcibly upon its surface, that these
gases are drawn into combination and form water, with a development of
heat sufficient to ignite the metal.
This power, whatever it may be, is common in both organic and inorganic
nature, and on its important purposes Berzelius has the following
remarks:--
“This power gives rise to numerous applications in organic nature;
thus, it is only around the eyes of the potato that diastase exists:
it is by means of catalytic power that diastase, and that starch,
which are insoluble, are converted into sugar and into gum, which,
being soluble, form the sap that rises in the germs of the potato.
This evident example of the action of catalytic power in an organic
secretion, is not, probably, the only one in the animal and vegetable
kingdom, and it may hereafter be discovered that it is by an action
analogous to that of catalytic power, that the secretion of such
different bodies is produced, all which are supplied by the same
matter, the sap in plants, and the blood in animals.”[206]
It is, without doubt, to this peculiar agency that we must attribute
the abnormal actions produced in the blood of living animals by the
addition of any gaseous miasma or putrid matter, of which we have, in
all probability, a fearful example in the progress of Asiatic cholera;
therefore the study of its phenomena becomes an important part of
public hygiène.
Physical research has proved to us that all bodies have peculiar
powers, by which they condense with varying degrees of force gases
and vapours upon their surfaces; every body in nature may, indeed, be
regarded as forming its own peculiar atmosphere. To this power, in all
probability, does catalysis belong. Different views have, however,
prevailed on this subject, and Dr. Lyon Playfair[207] argues that the
catalytic force is merely a modified form of chemical affinity, exerted
under peculiar conditions.
Whatever may be the power producing chemical change, it acts in
conformity with some fixed laws, and in all its transmutations, an
obedience to a most harmonious system is apparent.
It is curious to observe the remarkable character of many of these
natural transmutations of matter, but we must content ourselves with a
few examples only. For instance:--
Sugar, oxalic acid, and citric acid are very unlike each other, yet
they are composed of the same elements; the first is used as a general
condiment, the second is a destructive poison, and the third a grateful
and healthful acid: sugar is readily converted into oxalic acid, and
in the process of ripening fruits nature herself converts citric acid
into sugar. Again, starch, sugar, and gum would scarcely be regarded
as alike, yet their only difference is in the mode in which carbon,
hydrogen, and oxygen combine. They are composed of the same principles,
in the following proportions:--
Carbon. Hydrogen. Oxygen.
Starch 12 10 10
Sugar 12 11 11
Gum 12 11 11
These _isomeric_ groups certainly indicate some law of affinity which
science has not yet discovered. Similar and even more remarkable
instances might be adduced of the same elements producing compounds
very unlike each other; but the above have been selected from their
well-known characters. Indeed, we may state with truth that all the
varieties of the vegetable world--their woody fibre--their acid or
alkaline juices--the various exudations of plants--their flowers,
fruit, and seeds, and the numerous products which, by art, they are
made to yield for the uses of man, are, all of them, compounds of these
three elements, differing only in the proportions in which they are
combined with nitrogen, or in some peculiar change of state in one
or other of the elementary principles. The chemist is now enabled by
simple processes, from the refuse of manufactories to produce fruit
essences which are equal in flavour to the natural production; and from
benzoic acid, which is obtained in great abundance from the houses in
which cows are kept, the most delicate essences are produced, which
are given to the world as the distillations of a thousand flowers.
By the impulse given to organic chemistry by Liebig, our knowledge
of the almost infinite variety of substances, in physical character
exceedingly dissimilar, which result from the combination of oxygen,
hydrogen, and carbon, in varying proportions, has been largely
increased. And the science is now in that state which almost causes
a regret that any new organic compounds should be discovered, until
some industrious mind has undertaken the task of reducing to a good
general classification the immense mass of valuable matter which has
been accumulated, but which, for all practical purposes, remains nearly
useless and unintelligible.
These combinations, almost infinitely varied as they are, and so
readily produced and multiplied as to be nearly at the will of the
organic analyst, are not, any of them, accidental: they are the result
of certain laws, and atom has united with atom in direct obedience
to principles which have been through all time in active operation.
They are unknown; the researches of science have not yet developed
them, and the philosopher has not yet made his deductions. They are
to be referred to some secret fixed principles of action, to a force
which has impressed upon every atom of the universe its distinguishing
character. Chemistry makes us familiar with a system of order. The
researches of analysts have proved that every body has a particular
law of combination, to which it is bound by a mathematical precision;
but it is not proportional combination alone we have to consider. If
_allotrophy_ is evidenced in the mineral world, it is certainly far
more strikingly manifested in the vegetable and animal kingdoms.
There are some cases in which bodies appear to combine without any
limitation, as spirit of wine and water, sulphuric acid and water;
but these must be considered as conditions of mixture rather than of
chemical combination.
The composition of bodies is fixed and invariable, and a compound
substance, so long as it retains its characteristic properties, must
consist of the same elements united in the same proportions. Thus,
sulphuric acid is invariably composed of 16 parts of sulphur and 24
parts of oxygen. Chalk, whether formed by nature or by the chemist,
yields 43·71 parts of carbonic acid, and 56·29 parts of lime. The rust
which forms upon the surface of iron by the action of the atmosphere,
is as invariable in its composition as if it had been formed by the
most delicate adjustment of weight by the most accurate manipulator,
being 28 parts of iron and 12 parts of oxygen. This law is the basis of
all chemical inquiry, all analytical investigations depending upon the
knowledge it affords us, that we can only produce certain undeviating
compounds as the results of our decompositions. We are not in a
position to offer any explanation which will account for these constant
quantities in combination. The forces of cohesion and elasticity
have been advanced in explanation, on the strength of the fact that
the solubility of a salt in water is regulated by cohesion, and that
of a gas by its elasticity. Although it may appear that some cases
of chemical combination are due to these powers,--as, for instance,
when the union of oxalic acid or sulphuric acid with lime produces
an insoluble salt,--we cannot thus explain the constant proportions
in which the metals, sulphur, oxygen, and similar bodies, unite. It
is quite certain there is a power or principle, which we have not
yet reached, upon which are dependent all the phenomena which we now
embrace under the term chemical affinity.
Another law teaches us that when compound bodies combine in more than
one proportion, every additional union represents a multiple of the
combining proportion of the first. With the difficulty which arises
from the sub-multiple compounds we cannot deal:--further research may
render their laws less obscure. We have seen that 8 parts of oxygen
unite with 1 of hydrogen and 14 of nitrogen. It also unites with 110 of
silver, 96 of platinum, 40 of potassium, 36 of chlorine, and 200 parts
of mercury, giving rise to--
Water 9
Nitrous oxide 22
Oxide of silver 118
Oxide of platinum 104
Potash 48
Oxide of chlorine 44
Oxide of mercury 208
In these proportions, or in multiples of them, and in no others, will
these bodies unite with the acids or other compounds. It will, of
course, be understood that any other numbers may be adopted, provided
they stand in the same relation to each other.[208]
From the discovery of these harmonious arrangements was deduced the
beautiful atomic theory to which allusion has been already made.
Indeed, there does not appear to be any other way of explaining these
phenomena than by the hypothesis that the ultimate atoms of bodies have
_relatively_ the weights which we arbitrarily assign to them, as their
combining quantities. These views are further confirmed by the fact,
that gaseous bodies unite together by volume in very simple definite
proportions:--100 measures of hydrogen and 200 measures of oxygen form
water; 100 measures of oxygen and 100 measures of vapour of sulphur
form sulphurous acid gas. Ammoniacal gas consists of 300 volumes of
hydrogen and 100 volumes of nitrogen, condensed by combination into 200
volumes; consequently, we are enabled most readily to calculate the
specific gravity of ammoniacal gas. The specific gravity of nitrogen
is 0·9722, that of hydrogen 0·0694. Now, three volumes of hydrogen are
equal to 0·2082: this added to 0·9722 is equal to 1·1804, which is
exactly the specific gravity obtained by experiment.
There is no doubt, from the generality with which this law of volumes
prevails, that it would be found to extend through all substances,
provided they could be rendered gaseous; in other words, there is
abundant proof to convince us that throughout nature the process of
combination, in the most simple ratio of volumes, is in operation to
produce all the forms of matter known to us.
It has been shown, by the investigations of Dr. Dalton, in 1840, that
salts, containing water of crystallization, dissolve in water without
increasing the bulk of the fluid more than is due to the liquefaction
of the water which these salts contain; while Joule and Playfair
have shown that the anhydrous salts take up no space in solution.
From this we are naturally led to conclude that the volume occupied
by a salt in the solid state has a certain relation to the volume of
the same salt when in solution, and has also a fixed relation to the
volume occupied by any other salt. The law appears to be:--the atomic
volume of any salt whatever (anhydrous or hydrated) is a multiple of
11, or of a number near 11, or a multiple of 9·8 (the atomic volume
of ice), or the sum of a multiple of 11 or 9·8. Marignac, who has
also paid much attention to the subject, does not think these numbers
absolutely correct, but approximately so.[209] It would be a beautiful
exemplification of the simplicity of Nature’s operations, if it should
be clearly proved that the atomic volume of solid water (ice) regulated
the combining proportions by volume of all other bodies,--that it was
the standard by which chemical combination and ordinary solution were
determined.
In addition to the laws already indicated, there appear to be some
others of which, as yet, we have a less satisfactory knowledge, and,
as a remarkable case, we may adduce the phenomena of _substitution_,
or that power which an elementary body, under certain conditions,
possesses, of turning out one of the elements of a compound, and of
taking its place.[210] Thus, the hydrogen of a compound radical, as
carburetted hydrogen, may be replaced by chlorine, equivalent for
equivalent, and form a chloride of carbon, which being constructed
on the same type as the original, will have the same general laws of
combination.
Under the influence of these laws, all the combinations which we
discover in nature take place. The metals, and oxygen, and sulphur,
and phosphorus unite. The elements of the organic type, entering into
the closest relations, give rise to every form of vegetable life. The
acids, the gums, the resins, and the sugar which plants produce; and
those yet more complicated animal substances, bone, muscle, blood, and
bile; albumen, casein, milk, with those compounds which, under the
influence of vital power, resolve themselves into substances which are
essential to the existence, health, and beauty of the animal fabric,
are all dependent on these laws. But these metamorphoses must be
further considered in our examination of the more striking cases of
chemical action. The changes which result from organic combination are
so remarkable, and withal they show how completely the whole of the
material world is in subjection to chemical force, and every variety
of form the result of mysterious combination, that some particular
reference to these metamorphoses is demanded.
In nearly all cases of decided chemical action, all trace of the
characters of the combining bodies disappear. We say decided chemical
action, because, although sulphuric acid and water combine, and
salts dissolve in water, we may always recognize their presence, and
therefore these and similar cases cannot be regarded as strict examples
of the phenomena under consideration.
Hydrogen and oxygen, in combining, lose their gaseous forms, and are
condensed into a liquid--water. Sulphuric acid is intensely sour and
corrosive; potash is highly caustic; but united they form a salt
which is neither: they appear to have destroyed the distinguishing
characters of each other. Combined bodies frequently occupy less space
than they did previously to combination, of which numerous particular
instances might be adduced. Gases in many cases undergo a remarkable
condensation when chemically combined. In slaking lime, the water
becomes solid in the molecules of the hydrate of lime formed, and the
intense heat produced arises from the liberation of that caloric which
had been employed to keep the water liquid. When a solid passes into
the liquid state, cold is produced by the abstraction from surrounding
objects of the heat required to effect fluidity. An alteration of
temperature occurs whenever chemical change takes place, as we have
already shown, with a few trivial and uncertain exceptions. The
disturbance caused by the exercise of the force of affinity frequently
leads to the development of several physical powers.
Changes of colour commonly arise; indeed, there does not appear to be
any relation between the colour of a compound and that of its elements.
Iodine is of a deep iron-grey colour; its vapour is violet; yet it
forms beautifully white salts with the alkalies, a splendid red salt
with mercury, and a yellow one with lead. The salts of iron vary from
white and yellow to green and dark brown. Those of copper, a red metal,
are of a beautiful blue and green colour, and the anhydrous sulphate is
white.
Isomorphism, which appears in a very remarkable manner among the
organic compounds, has, under the head of crystallization, already had
our attention. There is also a class of bodies which are said to be
_isomeric_; that is, to have the same composition, although different
in their physical characters. But the idea that bodies exist, which,
although of a decidedly different external character, are of exactly
the same chemical composition and physical condition, is not tenable;
and in nearly all the examples which have been carefully examined, a
difference in the aggregate number of atoms, or in the mode in which
those atoms have respectively arranged themselves, or that peculiar
physical difference designated by the term _allotropy_, has been
detected.
Oil of turpentine and oil of lemons have the same composition, each
being composed of five equivalents of carbon and four of hydrogen.
These substances form, from the striking difference perceptible in
their external characters, a good example of isomerism.
The laws of organic chemistry are not, however, the same as those
applying to inorganic combinations. Organic chemistry is well defined
by Liebig, as the chemistry of compound radicals; and under the
influence of vitality, nature produces compounds which have all the
properties of simple elements.[211]
When we reflect upon the conditions which prevail throughout nature,
with a few of which only has science made us acquainted, we cannot fail
to be struck with the various phases of being which are presented to
our observation, and the harmonious system upon which they all appear
to depend.
When we discover that bodies are formed of certain determinate atoms,
which unite one with another, according to an arithmetical system, to
form molecules, which, combining with molecules, observe a similar law,
we see at once that all the harmonies of chemical combination--the
definite proportions, laws of volume, and the like--are but the
necessary consequences of these simple and guiding first principles.
In the pursuit of truth, investigators must discover still further
arrangements, which, from their perfection, may be compared to the
melodious interblending of sweet sounds, and many of the apparently
indeterminate combinations will, beyond a doubt, be shown to be as
definite as any others. But we cannot reflect upon the fact that these
atoms and these molecules are guided in their combinations by impulses,
which we can only explain by reference to human passions, as the term
_elective affinity_ implies, without feeling that an impenetrable
mystery of a grand and startling character in its manifestations
surrounds each grain of dust which is hurried along upon the wind.
We now, habitually, speak of attraction and repulsion--of the affinity
and non-affinity of bodies. We are disposed, from the discovery of the
attractive and repelling poles of electrified substances, to regard
these powers in all cases as depending upon some electrical state, and
we write learnedly upon the laws of these forces. After all, it would
be more honest to admit, that we know no more of the secret impulses
which regulate the combinations of matter, than did those who satisfied
themselves by referring all phenomena of these kinds to sympathies
and antipathies: terms which have a poetic meaning, conveying to the
mind, with considerable distinctness, the fact, and giving the idea
of a feeling--a passion--involving and directing inanimate matter,
similar to that which stirs the human heart, and certainly calculated
to convey the impression that there is working within all things a
living principle, and pointing, indeed, to “the soul of the world.” The
animated marble of ancient story is far less wonderful than the fact,
proved by investigation, that every atom of matter is penetrated by a
principle which directs its movements and orders its positions, and
involved by an influence which extends, without limits, to all other
atoms, and which determines their union, or otherwise.
We have gravitation, drawing all matter to a common centre, and
acting from all bodies throughout the wide regions of unmeasured
space upon all. We have cohesion, holding the particles of matter
enchained, operating only at distances too minute for the mathematician
to measure; and we have chemical attraction, different from either
of these, working no less mysteriously within absolutely insensible
distances, and, by the exercise of its occult power, giving determinate
and fixed forms to every kind of material creation.
The spiritual beings, which the poet of untutored nature gave to the
forest, to the valley, and to the mountain, to the lake, to the river,
and to the ocean, working within their secret offices, and moulding
for man the beautiful or the sublime, are but the weak creations
of a finite mind, although they have for us a charm which all men
unconsciously obey, even when they refuse to confess it. They are like
the result of the labours of the statuary, who, in his high dreams of
love and sublimated beauty, creates from the marble block a figure
of the most exquisite moulding which mimics life. It charms us for a
season; we gaze and gaze again, and its first charms vanish; it is ever
and ever still the same dead heap of chiselled stone. It has not the
power of presenting to our wearying eyes the change which life alone
enables matter to give; and we admit the excellence of the artist, but
we cease to feel at his work. The creations of poetry are pleasing, but
they never affect the mind in the way in which the poetic realities
of nature do. The sylph moistening a lily is a sweet dream; but the
thoughts which rise when first we learn that its broad and beautiful
dark-green leaves, and its pure and delicate flower, are the results
of the alchemy which changes gross particles of matter into symmetric
forms,--of a power which is unceasingly at work under the guidance of
light, heat, and electrical force,--are, after our incredulity has
passed away--for it is too wonderful for the untutored to believe at
once--of an exalting character.
The flower has grown under the impulse of principles which have
traversed to it on the solar beam, and mingled with its substance. A
stone is merely a stone to most men. But within the interstices of
the stone, and involving it like an atmosphere, are great and mighty
influences, powers which are fearful in their grander operations, and
wonderful in their gentler developments. The stone and the flower hold,
locked up in their recesses, the three great known forces--light, heat,
and electricity: and, in all probability, others of a more exalted
nature still, to which these powers are but subordinate agents. Such
are the facts of science, which, indeed, are the true “sermons in
stones,” and the most musical of “tongues in trees.” How weak are the
creations of romance, when viewed beside the discoveries of science!
One affords matter for meditation, and gives rise to thoughts of a most
ennobling character; the other excites for a moment, and leaves the
mind vacant or diseased. The former, like the atmosphere, furnishes
a constant supply of the most healthful matter; the latter gives
an unnatural stimulus, which compels a renewal of the same kind of
excitement, to maintain the continuation of its pleasurable sensations.
FOOTNOTES:
[200] All the phenomena connected with volcanic action, and the
theories connected therewith, will be found in Dr. Daubeny’s work, _A
description of active and extinct Volcanoes, of Earthquakes, and of
Thermal Springs_. 1848.
[201] Graham’s _Elements of Chemistry_. New Edition.
[202] Graham’s _Elements of Chemistry_; and Brande’s _Manual_.
[203] Of these _tables of attraction_ the following may be taken as a
specimen:--
SULPHURIC ACID.
Baryta.
Strontia.
Potassa.
Soda.
Lime.
Magnesia.
Ammonia.
It thus appears that baryta separates sulphuric acid from its compounds
with all inferior substances, and that ammonia is separated from the
acid by all that are above it.
[204] Berthollet: _Essai de Statique Chimique_, 1803. Sir Humphry Davy,
in his _Elements of Chemical Philosophy_, has given an excellent review
of the views of Berthollet.
[205] _On certain combinations of a new acid, formed of Azote, Sulphur,
and Oxygen_; by J. Pelouze. Translated from Annales de Chimie, vol.
xvi., for Scientific Memoirs, vol. i. p. 470. _Some ideas of a new
force acting in the combinations of Organic Compounds_, by Berzelius:
Annales de Chimie, vol. lxi. The conclusion come to by this eminent
chemist is expressed in the following translation:--“This new power,
hitherto unknown, is common both in organic and inorganic nature.
I do not believe that it is a power which is entirely independent
of the electro-chemical affinities of the substance. I believe, on
the contrary, that it is merely a new form of it; but so long as we
do not see their connection and mutual dependence, it will be more
convenient to describe it by a separate name. I shall, therefore, call
it _catalytic power_: I shall also call _catalysis_, the decomposition
of bodies by this force--in the same way as the decomposition of bodies
by chemical affinity is termed analysis.”
[206] Berzelius: _Annales de Chimie_, vol. lxi.
[207] _On Transformations produced by Catalytic Bodies_: by Lyon
Playfair, Esq.; Phil. Mag., vol. xxxi. p. 191, 1847.--“Facts have been
brought forward to show that there is at least as much probability in
the view that the catalytic force is merely a modified form of chemical
affinity exerted under peculiar conditions, as there is in ascribing
it to an unknown power, or to the communication of an intestine motion
to the atoms of a complex molecule. Numerous cases have been cited,
in which the action results when the assisting or catalytic body is
not in a state of change; and attempts have been made to prove, by new
experiments, that the catalytic power exercises its peculiar power by
acting in the same direction as the body decomposing, or entering into
union, but under conditions in which its own affinity cannot always be
gratified.”
[208] Consult Graham’s Chemistry, _On Combining Proportions_.
[209] _Memoir on Atomic Volume and Specific Gravity._ Messrs. Lyon
Playfair and Joule.--Philosophical Magazine, vol. xxvii. p. 453, or
Transactions of Chemical Society of London. _Observations_ on the
above, by Professor de Marignac.--Bibliothèque Universelle, Feb. 1846.
_On the Relation of the Volumes of bodies in the solid state, to their
equivalents, or atomic weights_: by Professor Otto. _Studies on the
connection between the atomic weights, crystalline form, and density
of bodies_: by M. Filhol. Translated for the Cavendish Society, and
published in their Chemical Reports and Memoirs.
[210] _Comptes Rendus de l’Académie des Sciences_, 1840, No. 5. A good
translation of Dumas’s Memoir appeared in the Philosophical Magazine,
from which I extract the following familiar exposition of the laws of
substitution:--“Let me make a comparison drawn from a familiar order of
ideas. Let us put ourselves in the place of a man overlooking a game at
chess without the slightest knowledge of the game. He would soon remark
that the pieces must be used according to positive rules. In chemistry,
the equivalents are our pieces, and the law of substitutions one of the
rules which preside over their moves. And as in the oblique move of the
pawns one pawn must be substituted for another, so in the phenomena
of substitution one element must take the place of another. But this
does not hinder the pawn from advancing without taking anything, as the
law of substitution does not hinder an element from acting on a body
without displacing or taking the place of any other element that it may
contain.”--_Memoir on the Law of Substitutions, and Theory of Chemical
Types._
[211] Liebig’s _Chemistry in its application to Agriculture and
Physiology_: translated by Lyon Playfair, Ph. D. _Animal Chemistry, or
Chemistry in its application to Physiology and Pathology_: by Justus
Liebig; translated by Wm. Gregory.