294 Chemical Instruments and Operations. 
gas, can have, to that of any receiver, capable of sustaining 
the unbalanced atmospheric pressure, consequent to ex- 
haustion. It has been already mentioned that the accession 
- ean produced in an exhausted glass globe by filling it 
eae cannot be ascertained by an ordinary bal- 
ance. This led me to adopt another mode of manipula- 
tion, which I shail proceed to describe and explain. 
The weight’ of a bladder is exactly the same, however 
large or small the quantity of atmospheric air which it may 
include, provided the air which may be within it, be under no 
greater Sree than that without. Hence, if by means 
of a volumeter, we introduce a known quantity of any other 
gas, one hundred cubic inches for instance, whatever the 
bladder gains or loses in weight, will be the difference be- 
tween the weight of the gas introduced, and that of a like 
volume of air. If the gas be lighter, we must deduct the 
weight necessary to restore the equilibrium from 30.5 grains, 
which is the weight of one hundred cubic inches of air. The 
remainder will be the weight of one hundred cubic inches of 
the gas. A varnished silk bag might be preferable to a 
bladder. 
The accuracy of this process may always be subjected to 
trial, by ascertaining whether the weight of the bag or blad- 
der employed, is the same when nearly void, as when con- 
taining a volume of atmospheric air, equal to the volume of 
gas, which it is intended to weigh. When a bladder is used, 
it must be dry ; as otherwise the loss of moisture, during the 
experiment, may influence the result. 
_ It must be evident that this process is oe upon the 
idea, that the gravity of atmospheric air, has been already 
ermined with a sufficient degree of womans. 
As there is no na by which a bag, or bladder, can be 
“Sears air, so that a po ortion will not remain between 
ht be’ 7 and ‘hte, expelled as a mean of get- 
ting rid of oxygen 
