252 



Mr GRAHAM on the Law of 



as they are all condensible in the pores of the stucco. The fol- 

 lowing Table exhibits a summary of the results : 



TABLE 



OF EQUIVALENT DIFFUSION-VOLUMES OF GASES ; AIE = 1. 



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 determined by ex- 

 periments 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 circum- 

 stances, as regards uniformity of temperature, and to be fre- 

 quently repeated. The diffusion-bulbs might also be consider- 

 ably increased in size, and a greater minuteness of observation 

 attained. Even in the most successful experiments 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, sulphureted hydrogen, and sulphurous acid, the pro- 

 cess 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. 



