270 Prof. Graham on the Law of the Diffusion of Gases, 



acid. As brine boils at 222° or 224°, that is 1 1° or 12° above 

 the boiling point of water, we may suppose it to be propor- 

 tionally less vaporous at low temperatures, and take the ten- 

 sion of its vapour at 64° to be that of water at 53°, which 

 was also the dew-point. This was confirmed by confining 

 847 volumes of atmospheric air over brine at the time ; the 

 air was not expanded by vapour rising into it from the brine, 

 nor did it contract. 



The initial contents of the diffusion are therefore, 



Air and vapour 17* 



Carbonic acid gas 177*6 



Vapour 2*4 



197-0 



An expansion took place of 4 measures in ten minutes, and 

 of 40 measures in five hours. A standard tube of the same 

 diameter as the diffusion-tube, sealed at the top, had been filled 

 with carbonic acid and placed over brine, to mark the absorp- 

 tion of the gas. One measure of gas was absorbed during the 

 continuance of the above experiment. The expansion, there- 

 fore, in the diffusion-case has really been 41 and not 40, or, 

 probably even more than 41, as undoubtedly a greater ab- 

 sorption of gas by the brine occurred in the diffusion-tube 

 than in the standard-tube, from the motion of the liquid in the 

 former during the course of the expansion of its gaseous con- 

 tents, while the liquid in the other was quite at rest, and 177*6 

 — 1, or 176*6 carbonic acid gas only have been exposed to 

 diffusion. The diffusion was allowed to take place into the 

 open air, which had the same proportion of vapour as the car- 

 bonic acid. 



The specific gravity of carbonic acid gas is 1*527, of which 

 the square root is 1*2360, and the reciprocal of the square root 

 0*8091. Hence one volume air should replace 0*8091 car- 

 bonic acid gas, which is the theoretical diffusion-volume of 

 this gas. 



In the experiment, 176*6 carbonic acid are replaced by 

 217*6 air. 



Here, the expansion upon 176*6 carbonic acid being re- 

 placed by air is 41+ parts by experiment, while it is 41*68 

 parts by theory. 



The diffusion-volume of carbonic acid gas is, 

 0*812 by experiment, 

 0809 by theory. 



Exp, 2. — In another experiment, conducted in the same 

 manner, thermometer 64°, barometer 30*00, the initial con- 

 tents of the diffusion-tube were, 



