certain Gaseous Compounds. 205 



expansion of oil gas, which do not happen when the expansion 

 is gradual ; a striking result of the change being the separa- 

 tion of carbon from the gas. The effect referred to is exhibited 

 when oil gas, compressed into vessels by a power equal to 

 that of 30 atmospheres, is suddenly allowed to escape through 

 a small aperture into the air. It was first observed accidentally, 

 in consequence of the derangement of the valve of a large 

 apparatus, into which the gas had been compressed to 27 

 atmospheres. The gas escaped with immense velocity, and 

 when an examination took place of what had happened, it was 

 found that all the metallic part of the valve upon which the 

 gas had rushed was covered with a black, moist carbonaceous 

 substance, and the contiguous brick wall with dry, black carbon, 

 the moisture in this case having been absorbed by the brick. 

 Since that time, Mr. Gordon has repeatedly shewn the effect, 

 by allowing the gas to rush out with very great violence from a 

 portable lamp against a piece of white paper, which becomes 

 immediately covered with black carbonaceous deposit. 



The general conclusion is, that as the gas thus rapidly expands, 

 a partial decomposition takes place, and carbon !s separated. 

 If this explanation should ultimately prove, by further experi- 

 ments, to be true, it will be highly important, as affording an 

 instance of the exertion of mechanical and chemical powers 

 in those circumstances where they most closely verge upon each 

 other. At present, we have but little knowledge of such 

 phenomena, though the announcement in France of the pro- 

 duction of several new compound bodies, possessed of peculiar 

 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, 

 othenvise 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 



* Philosophical Transactions. 



