The peculiar manner in which hydrogen gas appears to dissolve solid substances,—as iron, potassium, sodium, sulphur, phosphorus, selenium, and arsenic, may be explained by regarding the results as a manifestation of the powers of chemical affinity over the forms of bodies. In like manner, the solution of salt in water, or the mixture of alcohol in that fluid, may be viewed as chemical phenomena, although usually considered as simple cases of solution or mixture: alterations of temperature and other physical changes taking place in either. If two masses of metal,—either tin and copper, for example,—are melted and combined, the united mass will not equal the bulk of the two masses. If a pint measure of oil of vitriol and an equal quantity of water are mixed together, the combined fluids will not fill a two pint measure.[28]
In these instances a large quantity of heat is rendered sensible, as if it had been squeezed out by the force with which the particles combined, from interstices, which were filled with, what we may be allowed to call, an atmosphere of heat. Hence we conclude that, amongst the influences determining the molecular constitution of a body, heat performs an important part. All these facts go to prove that the atoms which form the compound body, whatever may be its character, are disposed of as so many centres of force, which act by influences of a peculiar character upon each other. That these influences are dependent upon known physical forces is certain; but the laws by which the powers of the ultimate atom are altered remain still unknown.
In the great operations of nature, changes are produced which we cannot understand, and variations of condition do certainly occur, which may be regarded as instances of transmutation.
Amongst others, we may adduce the different states in which we know carbon to exist. We have the diamond with its beautiful light-refracting property, its hardness and high specific gravity, capable of being converted into graphite and coke.[29] Charcoal, graphite, and the diamond, are totally unlike each other, yet we know they are each composed of the same atoms. Charcoal is a black irregular substance, light, and readily inflammable; graphite is crystallizable; but the forms of its crystals cannot be referred to those of the diamond, and it burns with difficulty. The diamond occurs in the most regular and beautifully transparent forms; and it can be burned only at the highest artificial temperatures. We are, however, convinced by experiment that the brilliant and transparent gem is made up of the same atoms as those which go to form the dull black mass of charcoal. From diamonds, as is above stated, coke has been formed by the heat of the voltaic battery, and recent experiments have proved that the volatilized carbon constantly passing off from one of the poles of a sufficiently powerful battery, is deposited in a crystalline powder, possessing most of the properties, as it regards hardness, &c. of true diamond dust. What is the mystery of this? We know not. The peculiar conditions have been the subjects of anxious study; but science has not yet let in a ray of light upon the mystery. That a different state—it has been called an allotropic condition—is often induced in the same class of atoms is certain; and hence the variety of the resulting compounds. To continue our illustrations with carbon—may not its combinations, in uniform proportions with oxygen and hydrogen,[30] owe their differences to some allotropic change in the ultimate atoms of this element.
We know that silicon—the metallic base of flint—is capable of assuming two or more different states; and that sulphur, selenium, phosphorus, and arsenic, are susceptible of these remarkable changes in which, without the slightest variation in the chemical character, a complete change in the physical condition is produced. Copper, iron, tin, and manganese, are known to exist in at least two states of physical dissimilarity, and many of the rarer metals exhibit the same peculiarity.[31] Hence, may we not infer that some of those substances, which we now term elementary, are but altered conditions of the same element? The resemblance between many of those bodies strengthens the supposition. Iridium and platinum,—iron and nickel,—chlorine, bromine, iodine, and probably fluorine,—are good examples of these similarities, although these bodies are all distinguished by physical and chemical differences.
The light-refracting gem, which glistens on the neck of beauty, and is valued for its transparency, differs only from the rude lump of coke in its molecular arrangement. Chemistry teaches us that we may, without producing any disarrangement of the affinities, but by merely setting up molecular disturbance, effect decided changes, as is strikingly shown in the colour of iodide of mercury changing from red to yellow under slight influences of heat, and back again to red by a gentle mechanical disturbance. By a slight change, merely molecular, iron may be made to resemble platinum in its physical properties.[32] An iron wire plunged into nitric acid is attacked by the acid with violence; but if one extremity of the wire is heated in the flame of a spirit lamp, such a change of state is produced throughout the entire length of the wire, that if it be now plunged into nitric acid no effect is produced upon it. On studying this question, we find good reason for supposing that bodies which, though physically different, resemble each other in some of their properties, iodine, bromine, &c., are the results of different allotropic conditions which have been impressed upon the ultimate atoms, similar to those observed in the substances named. This hypothesis appears to be more in accordance with the great principles which we must conceive guided the labours of an Infinite Mind, than that which supposes a vast number of individual creations. It will be seen in the sequel that light, heat, electricity, and chemical action, have the power of producing yet more striking changes in the forms of bodies. Is it not probable that, according to the operations of these agents, either combined or separate, acting over different spaces of time, and under varying circumstances, in relation to the molecular forces, all those allotropic states may be produced? Hence bodies may be discovered, which,—from the imperfections of science,—resisting our means of analysis, must, for a time, be regarded as new elements, whereas they are possibly only altered states of the same substance.
The experiments of Faraday and of Plücker prove that all matter exists in certain polar conditions, having powers of mutual attraction and repulsion.[33] Are the molecular forces, so called, to be referred to any of those powers which are involved in the general term magnetic-polarity? Are they not probably the result of some ultimate principle of which these properties are but the modified manifestations? These questions will now be generally answered in favour of magnetism; but in our ignorance we should pause; the next generation will without doubt find another solution for the problem.
Franklin supposed the ultimate atoms of bodies to be surrounded by a subtile fluid or ether, which they have the power of condensing upon their surfaces with great force—and we have experiments showing that this is probable[34]—whilst he regarded the atoms of the ether itself as mutually repellent, thus establishing an equilibrium of forces. Æpinus reduced the hypothesis of Franklin to a mathematical theory; and Coulomb proved that the force with which the repulsion of the ethereal atoms and the attraction of the material molecules are produced, is, like universal attraction,—to whatever power that may be due,—regulated by the law of the inverse ratio of the square of the distance. These views are found, upon minute examination, to hold true to the phenomena with which inductive science has made us acquainted; and the striking manner in which, when submitted to the rigorous investigations of geometers, they agree with known conditions of electricity, appears certainly to favour the opinion that this power may be materially connected with these molecular arrangements.
Many of the phenomena which are connected with the magnetic influences also bear in a remarkable manner upon this inquiry. But, without the necessary proof of direct experimental evidence, it were as unphilosophical to refer the binding together of the molecules of matter to the agency of electricity, as it would be to adopt the theory of the hooked atoms of Epicurus, or the astrological dream of the sympathies of matter.[35]