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—

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:—

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—

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.