gations in the mean time, and may prove to be truer in the

end."

§ 1066. To this, we must however add, that the appeal to electrolysis, which may be in this instance made, in consequence of these compounds being conductors, decidedly negatives the hypothesis; and ammonium invariably travels as a cation to the platinode, instead of amidogen to the zincode of the battery, to which it would necessarily be directed, if it bore a strict analogy to oxygen and chlorine.

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Thus, with oxalate of ammonia we obtain NH, at the platinode, and C, O, at the zincode, in accordance with the ammonium theory and the binary theory of salts, while we ought to expect upon the amidogen theory NH, at the zincode; but we are hardly able to guess at the position to which the remaining elements would attain. If we suppose C, H2 to pass to the platinode, what is to become of O,? If we imagine them to accompany C, H, in what capacity will the elements travel together? C, H, O, would form a very strange cation to NH, as an anion; and if we determine that they should accompany NH, there is an end of the amidogen theory. When we recollect the precise manner in which the exchanging quantities must be balanced in the axis of the polar forces of the voltaic current, it is evident that such arrangements cannot for a moment be supposed to be equivalent to each other.

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§ 1067. We have thus illustrated the subject of chemical metamorphosis by the spontaneous changes which organic products undergo at ordinary temperatures, and under the influence of different chemical agents; we must yet add a few remarks upon the transformations which are determined by high artificial temperatures.

The exaltation of the chemical affinities of these compounds by heat, would naturally be supposed to disturb the unstable equilibrium of their arrangements; but the results are not so much under our command as in the preceding cases, in consequence of our not being able to regulate the application of this energetic agent. In applying it to any mass we have no means of determining its equal action, for its diffusion will vary with the mass, the conducting power, &c.; and a number of different reactions will be determined at different points, dependent upon their respective temperatures.

§ 1068. Thus we have already noticed (§ 1012), that in exposing lignin, or wood, to destructive distillation, we not only obtain acetic acid and pyroxylic spirit, which we have already examined and compared with the products of the more precise spontaneous metamorphoses of the isomeric substance sugar, but a variety of other products, some of which we now propose briefly to notice.

§ 1069. Creosote. The tar which is obtained by the distillation of wood contains a number of curious compounds, some of which stand in need of further examination. Creosote is obtained by repeated distillations and rectifications of the tar, in the form of an oil which sinks in water. It is digested in a solution of caustic potassa, exposed to the air, and then precipitated by the addition of an acid. When thus purified it is colourless, and possesses a penetrating odour of wood smoke: it has a sharp burning taste, with a specific gravity 1.037, boils at 400°, and burns with a strong smoky flame. It mixes with ether, alcohol, and water; with the latter of which it forms a definite hydrate.

It coagulates albumen, and in very small quantities preserves fibrin and muscular flesh from putrefaction. It unites with both acids and alkalies, but does not appear to form definite compounds with them.

§ 1070. Paraffin is also obtained from tar by a long and intricate process. It is a pure form of hydrocarbon, CH, but in what exact state of condensation has not been ascertained. It is a soft solid of a crystalline texture, transparent and colourless. It is inodorous and tasteless, fusible at 110°.6, and capable of distillation without change. Its specific gravity is 0.870. It burns like wax, without smoke or odour.

It is chemically distinguished by its remarkable indifference to the most powerful chemical agents. It is very soluble in alcohol and ether.

When rosin and fixed oils are subjected to destructive distillation, an almost numberless variety of hydrocarbons are produced, some solid and others liquid. The mechanical compression again of some of these produces another analogous

series, which were examined by Dr. Faraday; the most remarkable of which was named by him

§ 1071. Quadri-hydrocarbon. It is a liquid which is capable of ebullition at common atmospheric temperature, and may be distilled by the heat of the hand. It burns with a brilliant flame, and in its liquid state is the lightest known substance amongst solids and liquids, having a specific gravity of 0.627. The specific gravity of its vapour compared to air is

and it is probably the same compound as the light oil of wine or etherine, which we have described (§ 1000).

It is also produced by the destructive distillation of caoutchouc, or India rubber, which, as we have seen (§ 970), is a natural form of hydrocarbon, (C, H1).

§ 1072. The great masses of fossil fuel which are interspersed in different strata of our globe, are doubtless produced by the slow metamorphosis of vegetable matters under the influence of heat and pressure; and the usual products of their destructive distillation bear a general analogy to, and in many cases are identical with, those from wood. They vary in their proportions with the heat which has been applied in their production.

§ 1073. Naphthaline. This substance is obtained abundantly by rectifying coal-gas tar; it crystallizes in white silvery plates; specific gravity 1.048; melting-point 136°, and boilingpoint 413°. It sublimes rapidly at lower temperatures. It burns with a smoky flame, and possesses a very powerful peculiar odour. It is insoluble in water, but abundantly soluble in alcohol and ether.

Formula, Co H.

Like etherine it forms definite compounds with a great number of other substances; some of which are acids of an analogous constitution to that of the sulphovinic acid, &c.

§ 1074. One of the most interesting of the liquid products of the distillation of coal, is naphtha. It is a natural as well as an artificial product. It is obtained in considerable quantity from the shores of the Caspian Sea, and from parts of

Italy. Its specific gravity varies from .750 to .850. It has a strong bituminous penetrating odour; does not congeal at 0°; and burns with a strong smoky flame.

Formula, C6 H5

but from late experiments it is probably a compound of other principles; or, at any rate, other principles are produced in it by transformations dependent upon various circumstances.

§ 1075. But we must now bring these observations to a close; and as an excuse for not multiplying our illustrations of this part of our subject, and as exactly expressing our own sentiments upon the occasion, we cannot do better than quote the opinion of Professor Liebig, who has himself so successfully laboured, not only in the field of speculation, but in that of observation and experiment. "Science," he has very recently observed*, “has, especially within the last few years, been enriched with so many bodies of this kind, the products of destructive distillation, that it is much to be wished the labours of chemists were directed to more really useful objects; for things of this kind truly serve no other purpose than to swell the size of our manuals. * * * * These substances are not met with in organized nature; they perform no part which fixes our attention; it is much to be lamented that so few chemists follow the example of Mulder, who by his multiplied and accurate examinations into the LAWS of animal and vegetable chemistry, has opened a world of new discoveries. The most remarkable, most interesting, and most important researches in chemistry have little to do with figures.”

XXI. ATOMIC THEORY.

§ 1076. In the preparatory view of the forces with which matter has been endowed, which we have been presenting to the student of natural science, we set before him in the first place, the conception which the mind of Newton had formed of the atomic constitution of matter (§ 7). The same hypothesis may be traced back to the writings of Epicurus and his followers, and even to earlier times; and in this, as well as many other instances, we cannot but admire the acuteness of intellect

* Annalen der Chemie, &c., band 38, p. 203.

which at so early a period of philosophy, propounded speculations upon the constitution of the universe, which have stood their ground till the present advanced state of science. The intellectual vigour of the philosophers of antiquity, indeed, was capable of the grandest and most comprehensive views of nature, and often conducted them to the most sublime truths, but in attempting perpetually to soar above the vulgar paths of observation and experience, they speedily became confounded in the mists of error and conceit.

The atomic doctrine, although at first sight it might appear to belong exclusively to metaphysical science, has received its greatest support from the progress of chemistry in modern times; and Dr. Dalton, the great discoverer of the theory of multiple and equivalent proportions, clothed his views from the first in the language of this speculation: and, hence, the term atom is now often used by writers and lecturers as synonymous with equivalent.

The law of multiple proportions is, in fact, a necessary consequence of the atomic hypothesis; for if bodies combine only atom with atom, or one atom with two, &c.—the weight of such atoms having a fixed relation of weight to one another-it is clear that whatever may be the aggregate number of particles so combining, the total weight of one sort must be in the same proportion to the total weight of the other sort.

All the phenomena are, in fact, irreconcilable with the rival hypothesis of the infinite divisibility of matter.

§ 1077. With regard to the absolute weight, sizes, and numbers of the ultimate particles of matter, nothing of course can be determined; nothing, moreover, with regard to the absolute quantities of heat, electricity or attraction with which they may be associated or endued; but speculations upon the relative proportions which the atoms of different species of matter bear to one another, in these respects, have been supported by experimental evidence and inductive reasoning of the most ingenious description. These, perhaps, are best kept out of sight in the first steps of physical investigations, as likely to turn the mind from that rigid method of induction from facts, by which alone the student can be safely guided; but in a more advanced stage they have their use in expanding the mind, and in imparting a lively interest to the subject. We shall therefore, conclude this view by illustrating the mode of reasoning,