504 On the Analysis of the 
In this case, the carbonic acid was 40 — 
21.5 = 18.5, and therefore exceeded in vo- 
lume the theoretical proportion (18.4) by 
only -,, a deviation much within the limits 
of possible errors, arising either from the 
difficulty of measuring small quantities, or 
of ascertaining the purity of the nitrous oxide. 
We may, also, from this mode of operating, 
deduce the quantity of nitrogen, which exists 
as an element of nitrous oxide; for since 1 
volume of carbonic acid results from the 
combustion of 1 volume of carbonic oxide, 
the residuary 21.5 measures must have con- 
tained 21_ 18.5 = 2.5 of carbonic oxide and 
nitrogen introduced by that gas, + 19 mea- 
sures of nitrogen disengaged from the nitrous 
oxide. 
The results of the experiments with an 
excess of carbonic oxide suggested to me a 
ready and correct method of testing the ni- 
trous oxide, which had hitherto been a desi- 
deratum. The only test, before applicable to 
this purpose, was the amount, to which the 
gas is absorbed, when agitated with well boiled 
water. But besides the uncertainty whether 
all the nitrous oxide be in this case condensed, 
the proportion of the unabsorbed residuum is 
subject to variation, from the quantity of other 
gases extricated from the water itself. Re- 
