Determination of the Surface Tensions of Jjiquids, 119 



the value of a be deduced for a third liquid, differences 

 between the values thus obtained and those communicated bj 

 Ramsay and Shields (loc. cit.), amounting to as much as ten 

 per cent., were obtained in some cases, although once in a 

 while a pretty good correspondence was observed. Jager's 

 equation appears to be merely approximate and does not stand 

 a severe scrutiny. Jager himself seems to hnd the justifica- 

 tion of his formula in its yielding results corroborative of 

 certain theoretical views he advances, and in the agreement 

 between his observed values and those calculated for the same 

 temperatures by means of temperature-coefficients ; but as the 

 temperature-coefficients were derived from his own data, which 

 rarely differ by more than five per cent, from those given by 

 Ramsay and Shields (loc. cit.), and as he does not attain a much 

 closer correspondence than that between his observed and cal- 

 culated values, the correctness of the formula does not seem 

 to be any the better established. 



It accordingly became peremptory to devise another for- 

 mula, which should be in better agreement with Ramsay and 

 Shields' measurements. But here a difficulty arose. Ramsay 

 and Shields determined the capillary constants of liquids when 

 freed from air; the liquids were in contact only with their own 

 vapor and glass. There is no doubt but that the surface ten- 

 sions of liquids can be accurately measured only when no air 

 is present, if the method consisting in the measurement of 

 the rise in capillary tubes be employed. R. Schiff * had 

 already made this observation before Ramsay and Shields. 

 Just what influence the presence of air has upon the capillar- 

 ity of liquids we do not know ; the greater or less volatility of 

 a liquid makes the degree of dilution of the air in contact 

 with its surface correspondingly greater or less. In the appa- 

 ratus described in this paper, ttie liquid under examination is 

 saturated with air, and the pressure of the air varies with the 

 density of the liquid. The difficulty at issue lies in the ques- 

 tion as to whether the indirect determinations made with 

 liquids in contact with air are comparable to more than a gross 

 approximation with those obtained by the direct method as 

 employed by Ramsay and Shields (loc. cit.). This difficulty 

 seemed at first insurmountable, but, finally, a simple relation 

 was discovered, which shows an excellent correspondence 

 between Ramsay and Shields' data and mine. 



The relation in question is 



(A) y=ichs + s^, 



where 7 represents the capillary constant in dynes per centi- 

 meter, c, the " apparatus constant," A, the distance between the 



*Lieb. Ann, ccxxxiii, p. 47. 



