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



water in the tube becoming saturated and abiding in it. But 

 the absorption of gas by water in the two experiments cannot 

 be well compared ; for, in the diffusion experiment, the chlo- 

 rine is rapidly diluted with return-air, which protects it from 

 absorption, and, indeed, before the end of the experiment, must 

 occasion a portion of the dissolved chlorine gas to reassume 

 the gaseous form, vapourizing away from the water which held 

 it in solution, and rising into the upper part of the tube. The 

 absorption in the diffusion-case would certainly be overrated 

 at one half of what occurred in the comparative experiment in 

 the same time. At the outset, however, we may presume that 

 the same absorption took place in both cases. Hence the ex- 

 pansion in the diffusion experiment would be 3 + 5, or 8 mea- 

 sures to the first eight minutes. The absorption, however, 

 would tell two ways in lessening the expansion ; first, so much 

 gas has disappeared by absorption, the quantity to be added 

 to the expansion ; second, so much less chlorine has really been 

 submitted to diffusion : 80 parts have not been diffused, but 

 80 diminished by this quantity. 



Merely adding the observed absorption in the first thirty- 

 nine minutes, namely, 18 measures to the expansion observed 

 of 19 measures, we have an expansion from diffusion of 37 

 measures, which approaches, as near as we can expect from 

 the method, to 4-5 measures, the theoretical expansion on 78 

 measures dry chlorine. We may therefore presume that the 

 diffusion of chlorine is not incompatible with the law. 



4. Sulphurous Acid Gas, — Over mercury. To diffusion- 

 tube with 7 measures air, 66 dry sulphurous acid gas were 

 added, which were allowed to diffuse into dry air. An ex- 

 pansion occurred of 



5 measures in 9 minutes 



13 23 



30 85 



31 108 



at which last expansion it remained steady. 



Assuming the specific gravity of sulphurous gas at 2*222, 

 its square root is 1*4907, of which the reciprocal is 0*6708. 

 67*08 sulphurous gas should be replaced by 100 air. 

 We have 66 sulphurous gas, and expansion 31, or, 

 66 sulphurous acid are replaced by 97*00 air, by experiment; 



66 * 98*39 air, by theory. 



The diffusion-volume of sulphurous acid gas is, 

 0*68 by experiment, 

 0*67 by theory. 



5. Protoxide of Nitrogen. — In an experiment with this gas, 

 dry, over mercury, allowing for a quantity of nitrogen which 



