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redness, in the retort over a charcoal fire ; the re- 
ceiver is to be kept cool, and the process continued 
as long as any elastic matter is generated. The 
condensible fluids will collect in the receiver, and 
the fixed residuum will be found in the retort. The 
fluid products of the distillation of vegetable sub- 
stances are principally water, with some acetous 
and mucous acids, and empyreumatic oil, or tar, 
and in some cases ammonia. The gases are car- 
bonic acid gas, carbonic oxide, and carburetted 
hydrogene ; sometimes with olifiant gas, and hydro- 
gene ; and sometimes, but more rarely, with azote. 
Carbonic acid is the only one of those gases rapidly 
absorbed by water ; the rest are inflammable ; ole- 
fiant gas burns with a bright white light ; carbu- 
retted hydrogene with a light like wax ; carbonic 
oxide with a feeble blue flame. The properties of 
hydrogene and azote have been described in the 
last Lecture. The specific gravity of carbonic acid 
gas, is to that of air as 20.7, to 13.7, and it con- 
sists of one proportion of carbon 11.4, and two of 
oxygene 30. The specific gravity of gaseous oxide 
of carbon, is, taking the same standard, 13,2, and 
it consists of one proportion of carbon, and one of 
oxygene. 
The specific gravities of carburetted hydrogene 
and olefiant gas are respectively 8 and 13 ; both 
contain four proportions of hydrogene ; the first 
contains one proportion, the second two propor- 
tions of carbon. 
If the weight of the carbonaceous residuum be 
added to the weight of the fluids condensed in the 
receiver, and they be subtracted from the whole 
i 2 
