13 Mr. J. J. Waterston on Capillarity 



the ratio of molecular volume of water and alcohol equal to 

 1:3177. 



To compute tliis same ratio from the relative volumes, we have 

 tbe following data : — 



Specific gravity of water at 68° F. . . . 1-000 

 „ water at 80° F. . . . -998 



„ alcohol at 8G° F. . . . '780 



„ „ steam 9* 



„ J, alcohol vapour . . . 23'16 



The quotient of relative volumes gives 1 to 3*294 as the value 

 of the above ratio. 



To find the change in Q that brings the first value of the 

 ratio to an equality with the second, let r = 3'29-l', and 



8;-=3-294-3-177 = 0-117. 

 It is easy to see by differentiating the equation for r, that 



Sr SQ* , 0-117 1 8Q 1 sn o -r -f fi 



-=-J ,henee3^^3:^ = g5= Q, and 8Q=2-7 if the error 



is in the capillary quotient for alcohol only, or SQ=l-5 if the 

 error is in the quotient for water only. In short, an error of 

 J^fth in either of the capillary constants is sufficient to account 

 for the discrepancy. Or if these were perfectly correct, then an 

 error of -j/^th in either one of the latent heats would make the 

 difference. 



§ 14. The data for sulphuric fether are less certain. The 

 specific gravity of the tether of commerce employed in deter- 

 mining the capillary quotient 261 was -7365 at 86° F., but pure 

 a;ther is only -7063 at that temperature. The latent heat of the 

 pure liquid, as determined by MM. Fabre and Silberman, is 

 163°'8 (F.) at its boiling-point. The latent heat of the a;ther 

 of commerce, according to Dr. Ure, is 302°. It is this last, which, 

 combined with the above value of Q, gives the absolute volume 

 of a molecule of ajther in the correct ratio to those of water and 

 alcohol. The difference between the numbers for latent heat is 

 certainly remarkable, and marks this liquid as one not adapted 

 to test the theory. We have also to note, that the rapid evapo- 

 ration of fcthcr must keep the superficial stratum of molecules 

 probably at a much lower temperature than the rest of the liquid ; 

 and as it is the surface particles alone that influence the capillary 

 force, the observed value of Q may be much too small. 



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