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 

 of weight, produced in an exhausted glass globe by filling it 

 with hydrogen, cannot be ascertained by an ordinary bal- 

 ance. This led me to adopt another mode of manipula- 

 tion, which I shall 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 compression, 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 predicated upon the 

 idea, that the gravity of atmospheric air, has been already 

 determined with a sufficient degree of accuracy. 



As there is no method by which a bag, or bladder, can be 

 exhausted of air, so that a portion will not remain between 

 its folds ; neither nitric oxide, nor phosphuretted hydrogen 

 could be weighed, by the process last mentioned, unless the 

 residual air were previously washed out by the gas to be 

 weighed, by hydrogen, or some other gas with which they 

 exercise no chemical reaction. A portion of nitric oxide 

 might be introduced, and then expelled as a mean of get- 

 ting rid of oxygen. 



