Mr. Hatchet t'j Obfervations on Bituminous Sub[tances y 143 



combuftion, 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 combuftion is long continued with the free accefs of air* 

 the whole of the carbon is diflipated in the ftate of carbonic acid ; 

 but in the procefs of putrefaction a confiderable portion of carbon 

 commonly remains even long after the putrid fermentation hat 

 ceafed. Although, therefore, it is as readily developed by putrefac- 

 tion as by combuftion, it is not, however, when liberated from the 

 other principles, fo fpeedily diflipated by the former as by the latter 

 procefs. 



According to the degree of combuftion within certain limits the 

 carbon is more or lefs apparent, and the like prevails according to 

 the degree of putrefaction ; fo that whenever the caufes which have 

 promoted this fpecies 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 have the appearance and properties of wood which 

 has been charred more or lefs. 



To this caufe, therefore, 1 am inclined to attribute the formation 

 and 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 v^etable oils and juices which have been partly modi- 

 fied bytmrherai agents*. 



The 



* " Coal not only forms the refiduum of all vegetable fubftances that have undergone 

 a flow and fmothered combuftion, that is, to which the free accefs of air hs- been pre- 

 vented, 



