Chemical Instruments and Operations... 295 
Another process suggested. 
I will take this opportunity of Ee ie 
suggesting, that the comparative <@) 
gravities of the gases might be : 
found, by means of two bodies, 
counterpoised, as represented in 
proportion to its bulk; an 
larger should be of glass, as thin 
as would be competent to sustain 
-the requisite changes of pressure; 
since | know of no body, equally | 
firm, and impervious, which would 
be as light in proportion to its 
bulk. ‘The changes of density 
being effected by the air-pump or 
condenser, might be measured by 
means of a barometer gage. 
Protoxide of nitrogen or nitrous oxide. 
This substance does not exist in nature. When artificial- 
ly obtained, it is gaseous; yet the experiments of Mr. Fara- 
day have taught us that under great pressure, It may be con- 
. 
verted into-a liquid. 
Means of obtaining nitrous oxide. 
It may be obtained by the action of dilute nitric acid upon 
zinc: by exposing nitric oxide gas to iron filings, sulphites, 
or other stibstances, attractive of oxygen. It is best procur- 
ed by exposing nitrate of ammonia to heat, and receiving the 
product in an apparatus described in the following article. 
