352 Prof. Graham on the Law of the Diffusion of Gases. 

 Table of Equivalent Diffusion-volumes of Gases; Air = I. 



Hydrogen 



Carburetted Hydrogen 



Olefiant Gas 



Carbonic Oxide 



Nitrogen 



Oxygen 



Sulphuretted Hydrogen 

 Protoxide of Nitrogen 



Carbonic Acid 



Sulphurous Acid 



Spec. Gravity 



0-694 



0-555 



0-972 



0-972 



0-972 



0-111 



1-1805 



1-527 



1-527 



2222 



In the diffusion-volumes of oxygen, nitrogen, and carbonic 

 oxide, the correspondence between theory and experiment is 

 as close as could be desired. Indeed, admitting our law, I 

 believe that the specific gravity of these gases can be deter- 

 mined by experiments on the principle of diffusion, with greater 

 accuracy than by the ordinary means. But, to be of value, 

 experiments performed with this important object in view, 

 would require to be conducted with extreme care, in the most 

 favourable circumstances, as regards uniformity of tempera- 

 ture, and to be frequently repeated. The diffusion-bulbs might 

 also be considerably increased in size, and a greater minute- 

 ness of observation attained. Even in the most successful ex- 

 periments recited in this paper, we cannot depend upon the 

 absolute accuracy of the third decimal figure. In the case of 

 carbonic acid gas, protoxide of nitrogen, sulphuretted hydro- 

 gen, and sulphurous acid, the process of diffusion is interfered 

 with in a greater or lesser degree by the absorbent action 

 which all porous bodies exercise upon gases. Fortunately, 

 however, the absorbent power of stucco is very low in degree. 



The density of any gas diffused into air, both being in the 

 same state as to aqueous vapour, is obtained by the formula 



■> - (.&■■ 



where G is the volume of gas submitted to diffusion, and A 

 the volume of return-air. In operating upon gases lighter 

 than air, the most useful instrument is a bulb of about two 

 inches in diameter blown upon half-inch tube, of which about 

 an inch may be left on either side of the bulb. The capacity 

 of the instrument, used as a gas-receive}* over water, is most 



