Experiments on the Gas from Coal. 423 
azote was found, than had been introduced as 
an impurity of the oxygen gas, it was con- 
sidered as having formed a part of the com- 
bustible gas. A single experiment on any 
kind of gas was never relied upon ; and to in- 
sure accurate results, the same gas was fired 
with different proportions of oxygen. De- 
ducting the pure oxygen found in the resi- 
due, from its quantity at the outset, the vo- 
lume of oxygen gas was learned, which had 
been spent in saturating a given measure of 
combustible gas. 
In gases free from all admixture with car- 
bonic oxide, it is easy to know how much of 
the oxygen consumed has been spent in satu- 
rating the charcoal; for as oxygen gas by 
conversion into carbonic acid suffers no change 
of volume, the quantity which has combined 
with the charcoal is exactly represented by 
the volume of carbonic acid produced by the 
combustion. For example, as 100 measures 
of olefiant gas afford by detonation 200 of 
carbonic acid, 200 measures of oxygen must 
have united with the charcoal of the ole- 
fiant gas. But beside these 200 measures, 
an additional 100 measures of oxygen are 
found to be consumed, and these must have 
combined with hydrogen, the other ingre- 
dient of the gas, the volume of which in its 
