so Diy? einen cae + + ica A&Q.z° ere YAEL Lf 
142 “Mr. Hatcuert’s Obfervations on Bituininous Subflatices. 
free accefs of air, the carbon enters into combination with et bp 
and caloric, and forms carbonic acid. pre 
We have many examplés’ in’ which ‘Carbon is formed or rather 
tiberated from thofe fubftances with which it was combined in 
vegetables; and thefe are now explained as effects fimilar to thofe 
of Pea NON: although fire has ‘not been the caufe. In both 
cafes the carbon has been freed from the more volatile principles 3 
and under circumftances ‘not favourable to the union of carbon 
with oxygen, the former muft neceffarily remain | More ¢ or lefs’ un- 
diminifhed. 
During the combuftion of vegetable matter, the more volatile 
principles contained in the vegetable fibre’ (which with carbon alf6 
form the refinous and other’ fimilar’: ‘fubftances) appear to be firft 
feparated ; and in proportion to this feparation, the other" more 
fixed fubftance, which we call carbon, is developed. 
‘Thus, by the progrefs of combuftion, wood becomes brown; and 
afterwards ‘black; fo that the ftate of the wood fhews the degree of 
combuftion to which it has been fubjeéted, or, in other words, how 
far the’ feparation | of the other’ principles: from carbon has been 
effected. 
Combuttion is..therefore a pe of analyfis by which the 
principles of vegetables are feparated, according to their ata 
‘and according to their degree of volatility. “By this operation 
hydrogen and azote (if it be prefent in the vegetable) are firft dif 
engaged and form, new combinations, while the carbon is the laft 
which is aéted upon; fo that unlefs a fufficient quantity of oxygen 
be prefent, it remains fixed and unchanged. 
“But the fame feparation of the vegetable principles happens 
whenever vegetables in the full poffeffion of their juices are expofed 
to circumftances which favour the putrid fermentation. —As in 
combuftion, 
