219 



to be proved, by the frequency with which they are found together, 

 but more particularly, by the exact agreement observable in their 

 chemical properties. In perfect agreement with peat, as well as 

 with, as we have just remarked, the products of the vinous fermen- 

 tation, the purer bitumens are composed of hydrogen, carbon, and 

 oxygen ; but, as might have been expected from the circumstances 

 under which their formation has taken place, no escape of the vola- 

 tile principles having been admitted, the new compound appears 

 to be the result of a high degree of concentration of these princi- 

 ples. The great degree of inflammability, possessed by all the 

 bitumens, manifests the large quantity of hydrogen which they con- 

 tain ; and the blackening of the clear and colourless naphtha, on 

 exposure to the air and light, shows the hydrogen to be saturated 

 with carbon. 



I cannot quit this subject, without pointing out the great obli- 

 gations which the lovers of chemistry owe to Mr. Hatchett, for his 

 ingenious observations on the nature of bitumens, and of the 

 changes which they undergo. The opinion which I have above 

 adopted, respecting the deposition of carbon, and the consequent 

 disposition to blackness in petroleum, asphaltum, &c. originated 

 with that gentleman, and is thus most concisely and happily ex- 

 pressed by him. "The progressive changes of naphtha into petro- 

 leum, mineral tar, mineral pitch, and asphaltun*, appear to be 

 caused by the gradual dissipation of part of the hydrogen of the 

 bitumen, and the consequent developement or disengagement of 

 carbon. Hence, I am inclined to believe, arise the changes of 

 colour, the degrees of inspissation, and the increased proportion 

 of carbon, found in those substances by chemical analysis I would 

 be understood, however, to mean that the carbon is only relatively 

 increased, in respect to the other ingredients, in a given quantity 

 of these bitumens, and that it predominates in proportion to the 

 dissipation of a certain portion of the hydrogen, which was origi- 



