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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 vo- 
latile principles having been admitted, the new compound appears 
to be the result of a high degree of concentration of these prin- 
ciples. • 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, foi 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 pe- 
troleum, mineral tar, mineral pitch, and asphaltum, appear to be 
caused by the gradual dissipation of part of the hydrogen of the 
bitumen, and the constjquent development 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- 
