OF ARTS AND SCIENCES. 381 



We find also that those coal carbo-hydrogens which afford most va- 

 pors are those which leave in their decomposition most allotropic car- 

 bon ; the natural bitumens affording the most remarkable and. con- 

 vincing results in this way. 



" As the mechanical state of the gas-carbon, clearly shown under 

 the microscope, as well as to the unassisted eye, is that of a solid left 

 from a transporting vapor, observation indicates that it has been thus 

 formed in the very compound atmosphere resulting from coal decom- 

 position. 



" It is a fact of chemical science, that defiant gas, when heated, 

 deposits carbon, and the fact can be easily demonstrated. But it is a 

 remarkable feature in this decomposition, that the gas deposits its car- 

 bon in the form of lampblack^ and the utmost reach of the means of 

 control will not produce an aggregation of particles resembling char- 

 coal. In high, or comparatively low temperatures, the deposition 

 never has the state of allotrojnc carbon, and, chemically speaking, 

 there is no evidence that this form of carbon can result from olefant 

 gas changes. 



" If, however, vapors of bitumen are mixed with the defiant gas, 

 these vapors suffer decomposition by heat, and we easily obtain in the 

 mixture vesicular, brilliant carbon in the allotropic state of gas-car- 

 bon : while the vapors solely much more readily afford this substance, 

 in form and composition closely resembling gas-carbon. 



" The subject, as I have studied it, appeared to possess interest in 

 connection with the new facts which M. H. St. Claire Deville has lately 

 published, respecting the graphitic form of Silicon, Boron, &c., in which 

 a similarity of conditions of production is essential to the effect being 

 obtained. 



" In geological theory, the formation of anthracitic carbon in one 

 case, and of graphite, with the gradations back to anthracite, in an- 

 other, has hardly been explained ; but if we are allowed to take the 

 allotropic state of carbon as a distinctive character of that carbon, 

 which has been sublimed, through the agency of its own, or more 

 likely a foreign vapor, then the occurrence of these forms of car- 

 bon ceases to be anomalous, and accords with the circumstances un- 

 der which many rocks have been produced. Graphite, graphitic car- 

 bon, graphitic oxide of iron, and, in general, sublimates composed of 

 vesicular forms presenting lamina?, under this view become a class 

 of bodies which owe their forms to the transporting power of va- 

 pors in motion. 



