220 On the Decomposition of certain Hydrocarbons, [ 1 827. 



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 in- 

 soluble, 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 hydro- 

 gen ; 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 sub- 

 stances 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 Institutionf upon the fluid pro- 

 duct 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 corks which closed the vessels, and 

 after a lapse of time, chemical changes were produced ; for 

 * Philosophical Transactions. t page 154. 



