Blackwood's Magazine/Volume 1/Issue 2/Chemical Process of Combustion

CHEMICAL PROCESS OF COMBUSTION.

It appears, from the notices inserted in the scientific journals, that the attention of Sir Humphry Davy is at present particularly directed to the consideration of the chemical process of combustion; and though we do not consider ourselves entitled to suppose that all our readers can possess that minute acquaintance with this subject, which might justify us in presenting it to them in considerable detail, we yet think, that on so very interesting a topic it is possible to convey such general information as may be sufficiently understood by every description of readers. No phenomenon, it is evident, presents a subject of more interesting speculation to a mind of just philosophical taste. The instantaneous transition from a state of darkness to that of clear and useful illumination, which is produced by the presence of a lighted taper—the beautiful form which the flame itself is disposed to assume—the varied tints which characterize this appearance from the mild blue of its base to the white or orange of its waving summit—and the unfailing steadiness with which it maintains its place, so long as the materials of its nourishment are afforded, present an assemblage of striking appearances, which, but for the inattention induced by its almost-habitual presence, is better fitted, perhaps, to awaken the interest of a thinking mind than any other phenomenon of daily occurrence. It is a fact, however, that the researches and theories of modern chemistry have as yet been able to advance but a very little way towards a satisfactory explanation of these appearances.—The most obvious supposition unquestionably is, that the light and heat which are essential to the phenomenon, are derived from the burning body itself—and this, accordingly, it. is universally known, was the opinion entertained by the followers of Stahl, whose doctrines exercised an unlimited influence, before the introduction of the present views, over the philosophers and chemists of modern Europe. According to this philosopher, then, combustion was merely the evolution from the burning body, when placed in circumstances adapted to this effect, of a peculiarly subtile and active principle, to which, from the ordinary appearance which its evolution assumes, he gave the name of Phlogiston—light and heat being those properties of this body by which it adapts itself to the observation of our powers of perception. This theory, we have said, from the high reputation which its author had obtained, was long unanimously adopted by philosophers—and being in perfect agreement with the most natural and obvious judgment of mankind, scarcely a suspicion was allowed to intervene, that there could be any thing imperfect or inaccurate in the theory. The progress of philosophical opinion upon this subject, however, presents, we think, a very instructive instance of a disposition which seems universally characteristic of mankind, that, we mean, of employing any favourite principle to account for every appearance which presents itself, however little warranted such an application may be by the circumstances most characteristic of the phenomenon in question. It is accordingly very generally known, that about the latter part of the last century, and while the doctrines of Stahl were in all their vigour, the existence and properties of oxygen were discovered, and immediately excited the utmost attention in all who were devoted to philosophical pursuits. The discovery was, in reality, both beautiful and instructive in a very uncommon degree. The increased illumination communicated by this gas to any ignited body which the operator immersed in it—the pure and apparently etherial nature of the gas itself—the very energetic properties it was found to possess—and the vast variety of bodies into whose composition it was discovered to enter—all contributed to point out this substance as one of the most important instruments in the economy of nature, and insensibly produced a very general disposition to receive its operation as a complete account of any former unexplained phenomena, with whose existence and properties it might have any connexion. While the minds of men, accordingly, were in this state, it was opportunely discovered, that when a burning body is introduced into a jar of common air, the mouth of the jar being at the same time inverted over water, the oxygenous portion of the air is altogether consumed, and the burning body is found to have acquired an additional weight, precisely corresponding with that of the oxygen which had disappeared. From this discovery it was immediately concluded, that combustion is in fact nothing else than the combination of oxygen with the combustible body—that the light and heat are the consequences of this combination, being necessarily given out by the combining oxygen—and that the whole process of combustion is explained, when it is stated to be the consequence of the separation of oxygen,—first, from the other constituent of the air, and next, from the light and heat which it contained before it began to experience this separation,—and also, of the combination of this gas with the body whose combustion was actually observed. A few of the more intelligent and cautious of the learned might still entertain a very invincible opinion, that the phenomenon in question had not really been accounted for but the great multitude of the studious, who seldom condescend to a very careful examination of any particular subject, received the doctrine as impregnably established—while, in the public demonstrations of professed teachers, the difficulties that remained were either entirely unnoticed, or were hastily concealed from the view of the curious, by ambiguous language, or unsatisfactory conjecture.

From the application of this statement, however, we conceive ourselves bound to exempt all the more enlightened and illustrious chemists. Sir Humphry Davy, we believe, in his public lectures, always expressed himself upon this subject with much becoming freedom of opinion and Dr Thomson has repeatedly stated, in his excellent system, that he still considered the explanation of the phenomena of combustion as in a very imperfect state. The opinion of this latter philosopher, indeed, if we are not much mistaken, has always coincided exactly with that which we are anxious at present to submit to the notice of our readers, viz. that in the common explanation of this phenomenon, only one of the circumstances connected with it, that is, the disappearance of the oxygen, had in reality been accounted for, while the exhibition of light and heat, which really constitute what is essential to the phenomenon, are altogether unexplained.

Conceiving that this view of the matter must now be very generally admitted, it is with much satisfaction that we perceive Sir Humphry Davy to be actively engaged in the investigation of what has justly been denominated the most important problem in chemistry. His attention seems to have been naturally directed to this investigation, by his recent invaluable discovery of the safety-lamp for coal mines, and by the very curious properties of flame which were suggested by that discovery; and he has accordingly read several papers, at different meetings of the Royal Society, detailing the experiments he has made, with the view of elucidating the properties of flame. His opinion, as recently expressed, seems to be, that flame consists of gaseous bodies heated above whiteness. Many other curious properties, however, of ignited bodies have been discovered by him in the course of his recent researches and we have little doubt, that before he relinquishes the investigation, he will either be able to go farther towards a solution of the difficulty than former experimentalists have been able to advance, or will at least succeed, by exhibiting an accurate statement of the case, in giving currency to a more scientific mode of considering this subject, than that which has so long been implicitly adopted by the multitude of more superficial and careless inquirers. It is at all times a treat of the highest kind, to follow the progress of scientific discovery but the gratification derived from this source is necessarily enhanced to an incalculable amount, when there seems reason to apprehend, as in the present instance, that the perseverance of the philosopher is on the point of being rewarded, by the developement of some views of prominent importance. The curiosity of a liberal mind admits, in fact, of no higher gratification (the delight of the discoverer himself excepted) than that of being permitted to watch the event.