196 



PROFESSOR THOMAS GRA.HAM S SCIENTIFIC WORK. 



every elongation of the capillary, a constantly' increasing deviation from 

 these rates was observed — the increase of the deviation, however, 

 becoming less and less considerable with each successive increment 

 of elongation, until, when the tube had acquired a certain length in 

 pro])ortion to its diameter, a maximum deviation of the relative rates of 

 passage of the ditferent gases from their relative rates of effusion was 

 arrived at. These ultimate rates of passage, unaffected in relation to 

 each other #by further elongation of the capillary, constitute the true 

 transpiration velocities of the different gases, as distinguished from their 

 velocities of effusion. Of all the gases experimented on, oxygen was 

 found to have the longest transpiration time, or slowest transpiration 

 velocity. In the following table its time of transpiration is taken as 

 unity, and the times of a few other gases compared therewith. In other 

 columns are given the specific gravities of the same gases, referred to 

 the specific gravity of air as unity; and the square roots of their specific 

 gravities, which also express their relative times of effnsion. 



Hydrogou . 

 Marsh gas . 

 Nitrogen .. 

 Oxygen ... 

 Carbonic g: 



V 



Specitic 

 gravity. 



Transpiration 

 time. 



That gas transpiration has no direct relation to gas specific gravity is 

 shown by the transpiration times of oxygen and nitrogen exceeding the 

 transpiration times both of the much lighter hydrogen and marsh gas, 

 and of the much heavier carbonic gas. Again, ammonia, olefiaut gas, 

 and cyanogen, Avith the diflerent si)ecific gravities .51)0, .978, and 1.806 

 respectively, have the almost identical transpiration times .511, .505, 

 and .500 ; or, approximatively, half the transpiration time of oxygen, 

 1.000. Nevertheless the transinration times of oxygen and nitrogen are 

 directly as their specific gravities: and farther, the specific gravities of 

 nitrogen, carbonic oxide, and nitric oxide being .071, .008, and 1.039, 

 their transpiration times are .877, .871, and .870 respectively. But then 

 olefiaut gas, with the same specific gravity .978, has the much shorter 

 transpiration time .505 ; and similarly in other cases. Altogether the 

 discordance between transpiration and specific gravity is of greater fre- 

 (jucncy than the accordance ; but still the circumstance of gases having 

 the same, or about the same, specific gravity, having also the same, or 

 about the same, rate of transpiration, is of too frequent occurrence to 

 be merely accidental. 



As a rule, the observed trausi)iration rate of a mixture of gases cor- 

 responded with the calculated mean rate of its constituents; but the 

 transpiration rates of the light gases, hydrogen- and marsh gas, Avere 



