Analysis of the compound inflammable Gases . 289 
to a mercurial cistern, where the proportion of carbonic acid is 
determined by liquid potash. The proportions of oxygen 
and nitrogen gases, in the unabsorbed residue, are learned by 
agitation with sulphuret of lime, observing the precautions 
which have been stated by De Marte The residuary 
oxygen being deducted from the quantity at the outset of the 
experiment, shews how much oxygen has been expended in 
the combustion of the inflammable gas. It is scarcely neces- 
sary to observe, that the gases are carefully reduced, at each 
stage of the operation, to a mean temperature and pressure, 
(6 o° of the thermometer, and 30 inches of the barometer).* 
The process of combustion, as thus stated in general terms, 
appears sufficiently simple. It is often, however, rendered 
complicated by the imperfect combustion of the inflammable 
gas, a part of which escapes through the orifice of the burner, 
either wholly unaltered, or only partially burned. As this 
portion is not absorbed by sulphuret of lime, it gives a falla- 
cious appearance of an actual addition of nitrogen to the 
oxygen gas remaining in the receiver b. I am unacquainted 
with any method of entirely obviating this difficulty ; but its 
amount may be diminished by an attention to certain precau- 
tions. With this view, the pressure upon the gas, contained 
in the receiver 00, should, on first opening the cocks q and r, 
be no more than is sufficient for its gentle expulsion through 
the tube s s. When, however, the stream is once kindled, the 
larger the flame, and the more active the combustion, within 
certain limits, the more completely is the gas consumed. It 
is necessary, also, to stop the combustion, before it is rendered 
* The rules observed in these calculations, are stated in my Epitome of Che* 
njistry, 5th edition, p. 441, 
P p 
MDCCCVUI. 
