466 Dr. Harry C. Jones on the 



more special, and can be employed for determining particular 

 kinds of ions. 



The " osmotic-pressure " and " boiling-point " methods are 

 at present, however, not sufficiently accurate to admit of 

 extensive application for this purpose. Some doubt has re- 

 cently been cast on the accuracy of the " solubility " method 

 for measuring dissociation, but it seems probable that the 

 method will be capable of yielding fair results in a limited 

 number of cases. The freezing-point method has hitherto 

 been open to the same objections as apply to the boiling- 

 point and osmotic-pressure methods. 



The " conductivity " method has been then, up to the 

 present time, by far the most accurate aud general method 

 for measuring dissociation. It has this particular advantage, 

 that it can be applied to very dilute solutions. 



The " freezing-point " method, as improved by Beckmann*, 

 is of limited application, since it cannot be used for very dilute 

 solutions ; indeed, it can scarcely be applied to solutions more 

 dilute than O'Oln. It has now, however, been so developed 

 that the dissociation of solutions as dilute as 0*004 or 0'005 n 

 can be fairly well determined. 



The Apparatus, 



The apparatus employed was essentially the same in prin- 

 ciple as that devised by Beckmann, in which every part was 

 very greatly enlarged. The thermometer used was made espe- 

 cially for this work, and the scale was divided directly into 

 thousandths of a degree, so that with a small lens one could 

 read accurately to a ten-thousandth part of a degree. This 

 thermometer was very carefully calibrated. The entire scale 

 corresponded to only 0'6° 0. 



The vessel in which the solution whose freezing-point was 

 to be determined was placed had a capacity of about 1200 

 cub. centim., and just a litre of the solution was used in each 

 determination. The remainder of the apparatus, designed 

 for the gradual cooling of the solution and for maintaining 

 constant temperature, is shown in drawings, figs. 1, 2, and 3, 

 Zeits. phys. Cliem. xi. p. 532. 



The form of stirrer there described has been found to be 

 very efficient. All currents produced on the upward stroke 

 of the stirrer were completely reversed on the downward. 

 In the later work, when solutions of alkalies and acids were 



* Beckmann, Zeits. phys, Chem. ii. p. 638, and vii. p. 324. 



