CAPILLARY ATTRACTION IN RELATION TO CHEMICAL COMPOSITION. 265 



however, is begging the whole question, for there is no other com- 

 pound with which to test the validity of this particular value. Schiff' s 

 formula is far better than the new ones in this instance, for the extra- 

 polated value of JV for water seems to agree tolerably well with the 

 actual value. 



The next thins; to be considered is the mode of measuring 1 the 

 constant. The capillary height multiplied by the specific gravity 

 and divided by 2 does not represent the capillary constant or the 

 surface tension ; for according to the theory of capillary attraction 

 pV=Tl cos i or V=a*l eus i. where V is the volume of the liquid raised 

 in the tube, p is the density. / the internal perimeter of the tube, T 

 the surface tension, ar the capillary constant . i the contact angle. 

 When a circular tube is used as in the experiment of Schiff and most 

 other investigators, £(=2lfr) might be measured with fair approxi- 

 mation ; V can also be found oui with tolerable accuracy, but it is 

 next to an impossibility to measure i in the tube method. As has 

 been criticized by Volkmann, Schiff made an unwarrantable assumption 

 that i is always zero in the liquids investigated by him, and calculated 

 out or accordingly. But as the value of i in the various liquids 

 investigated by Schiff appears to be pretty large, especially in the 

 case of chloroform, what he calls the capillary constant of a substance 

 at the boiling point cannot be accepted as such indiscriminately ; and 

 the more so, since, as he himself points out, i changes with rise of 

 temperature, and since the boiling points of many liquids given in 

 his communications are somewhat high, i cannot be zero even where 

 it is so at ordinary temperatures. Volkmann has calculated the value 

 of i for all the liquids contained in the first communication of Schiff's, 

 from the height of the meniscus given in the paper. But, as Schiff 

 replies, the meniscus height is undoubtedly one of the most difficult of 

 quantities to measure. Indeed, the recalculation made by Volkmann 



