Mr, ap SSERtT: Obfervations on Bituminous Subflances. 143 
combuttion, fo by the progrefs of putrefaction does the vegetable 
lofe its colour, become brown, and afterwards black; at the fame 
time a gas is difcharged, which is compofed of hydrogen, azote, and 
carbonic acid, 
_ When combuttion i is long continued with the free accefs of airy 
the whole of the carbon is diffipated in the ftate of carbonic acid ; 
but in the procefs of putrefaétion a confiderable portion of carbon 
commonly remains even long after the putrid fermentation has 
ceafed, Although, therefore, it is as readily developed -by putrefac- 
tion as by, combuttion, it is not, however, when liberated from the 
other principles; fo fbeedily diffipated by the former as by the latter 
procets. Siysu 
According to the eres an edo llbiong within certain limits the 
carbon is more or Jefs, apparent, and the Jike prevails according to 
the degree of putrefaction; fo th at. whenever the caufes which have. 
promoted ;this {pecies of fermentation have ceafed, the vegetable 
fubftance, will remain,with more or lefs of its firft principles, and 
-with more or lefs. vifible carbonic matter, according to the degree of 
“putrefaction which, has. prevailed, | and. the vegetable fubftance will 
confequently haye the appearance. and properties of wood which 
has been charred more or lefs.. 
To this caufe, therefore, I am inclined to attribute the Senied 
ind appearance of the Bovey coal and furturbrand; and I believe 
that the portion of oily and bituminous matter, which I have ob- 
_tained from them by diftillation, is nothing more than the remain- 
der of the vegetable oils asa juices ieee have been partly modi- 
fied by miner al agents*. piivrabawpns. 
. reHA if } The 
o trots ¥2 pitied 3 igs ' ?lesiTs ; n 
'* « Coak side city opti the Gaeintaar all’ vegetable fubftances that have undergone - 
a flow and forthe ree ae that i (oh to'which the free accefs of air has been pre- 
ar he vented, 
