Page:Popular Science Monthly Volume 7.djvu/716

696  of theories which may be formed on the slender foundation of one or two facts, I am convinced that it is the business of the true philosopher to avoid them altogether. It is more laborious to accumulate facts than to reason concerning them; but one good experiment is of more value than the ingenuity of a brain like Newton's."—Quarterly Journal of Science.



HE correctness of the old and well-founded conception that the light of flame is caused by incandescent carbon-molecules, has been disputed by Dr. Frankland, who contends and tries to prove that it is derived from hydrocarbon-vapors. It is evident that the old theory would have to give place to the new doctrine as soon as the untenability of the former and the correctness of the latter are proved. But neither the one nor the other has, I think, yet been done. Prof. Frankland can, therefore, only be pleased if the present paper subjects the pros and cons of the new and old theory to an impartial examination.

As proof of his ideas he mentions that the soot deposited on a cool surface, when introduced into a flame, does not consist of pure carbon, but that it contains also hydrogen; that, in fact, it seems nothing else than a collection of the densest light-giving hydrocarbons, whose vapors condense on the cold surface.

Against this we may mention that not only do the heavy hydro-carbons, but even marsh-gas, split up at high temperatures on exclusion of atmospheric air; and as the hydrocarbons, whose vapors are supposed to cause the luminosity of the flame, are precisely under such conditions before they come into contact with the air, it cannot be doubted that they suffer decomposition into carbon and hydrogen in the luminous portion of the flame. It is of little importance whether the eliminated carbon is chemically pure, or whether it contains still a hydrogen compound; the important question is this, Is the soot held by the flame in the shape of vapor or in the solid form? If the soot was nothing but a conglomeration of the densest light-giving hydro-carbons, whose vapors condense on a cool body, then, when sufficiently highly heated by exclusion of air, it ought to reassume vapor-form. This is, however, not the case, as every one will find who tries the experiment.

Its chemical composition is just as little favorable to Frankland's view. It ought, presumedly, to vary according to the lighting material from which it was derived—nay, even according to the place of 