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220 properties, solely by the exertion of physical powers, may lead us to hope for an accession of information on the subject; that which we thought we had, was in part rendered uncertain by the contrary conclusions arrived at by Mr. Perkins and Dr. Brewster, the one believing that in a case of crystallization the effect was produced entirely in consequence of pressure" ; the other, that pressure had been the only cause why bodies, otherwise ready to crystallize, had retained the fluid state.

A natural suspicion, upon first hearing of and seeing the results obtained by Mr. Gordon, was, that the rapidity of the current of gas had carried away a minute portion of the metal from the surface of the valve past which it rushed, or of the interior of the air-way against which it was thrown, and that that metal had caused the stain upon the paper; but upon examination this proved not to be the case; for the black deposit upon a card, when subjected to acids, remained insoluble, and when burnt and tested chemically, gave no traces of copper.

Further examination of the substance showed that it was not a pure carbon, but one of those compounds, containing a very large proportion of carbon, combined with a small quantity of hydrogen; being analogous to tar, pitch, or asphaltum. It dissolved readily in the fluid hydrocarbons obtained by the compression of oil-gas. As these black carbonaceous compounds are formed in the process of making oil-gas, a suspicion cannot but arise, that the effect observed may have been produced by the current of gas having swept off small portions of such substances previously deposited, or slowly formed in the interior of the vessels at former periods; and have left them upon the wall in the accidental result, or upon the paper placed in the current of the gas, when the effect has been purposely shown.

It may, however, be remarked, that in experiments made in the laboratory of the Royal Institution upon the fluid product obtained by condensing oil-gas at high pressures, it was observed, after rectifying the products and separating the more fixed from the more volatile, that although they were perfectly clear and transparent at first, yet by spontaneous evaporation through the cork which closed the vessels, and after a lapse of time, chemical changes were produced; for