196 



Mr. W. C. D. Whetham. 



Some of the stock solutions for the early part of the work were 

 prej)ared by Miss D. Marshall, and most of those used in the later 

 measurements were made up at the Cambridge University Chemical 

 Laboratory by Mr. G. Hall, under the advice of Mr. H. J. H. Fenton. 

 Others were prepared by the writer from recrystallised salts obtained 

 from Kahlbaum, of Berlin. 



From a knowledge of the weight of solvent used and the weight of 

 stock solution added it was easy to calculate the concentration (m) of 

 the resulting solution in terms of gramme-equivalents of solute per 

 thousand grammes of solution. All the experiments were made on solu- 

 tions so dilute that this way of defining m leads to practically the same 

 results as though the gramme-equivalents of solute were referred to 1000 

 grammes of solvent, or to one litre of solution. The differences only 

 become visible on the curves in the cases of two or three of the 

 strongest solutions of some of the substances used. 



The observed resistance is corrected for any slight difference in 

 temperature from zero, and for the increased volume of liquid in the 

 cell due to the volume of stock solution added. 



The reciprocal of this corrected resistance is the conductivity in 

 arbitrary cell units, and from this the corresponding arbitrary con- 

 ductivity of the solvent is subtracted. The resultant conductivity, 

 due to the added solute alone, is divided by and Z;/m, the equivalent 

 conductivity, plotted on a diagram as ordinate, the value of iii^, a 

 number proportional to the average nearness of the molecules, being 

 used as abscissa. From these curves the maximum value of hjin is 

 estimated, and taken to represent complete ionisation, the ionisation 

 for the solutions measured being calculated as the ratio between the 

 actual value of kjm and its maximum. 



The values obtained for these ionisations were arranged as shown 

 in the following table, which is given as an example, and are plotted 

 as curves on the diagrams appended. 



Sulphuric Acid. — Prepared at the Chemical Laboratory by adding the 

 calculated amount of SO3 to distilled acid. Successive crystallisation 

 brought the melting point of the resultant H2SO4 to + 10'5° Cent. 

 The crystals were dissolved in water and the concentration of the 

 solution estimated by the barium sulphate method. 



Similar measurements were made on Potassium Chloride, Barium 

 Chloride, Copper Sulphate, Potassium Permanganate, Potassium Ferri- 

 cyanide, and Potassium Bichromate. 



In discussing the results, we may first notice that, in cases where 

 it has been possible to obtain values for the ionisation at 18° from 

 Kohlrausch's work, the ionisation curve at 0° is appreciably different 

 from that at 18°, the ionisation falling off more rapidly with increasing 

 concentration at <:he higher temperature. In the diagrams the values 

 for 0° are given by dots inside circles, and those for 18° by crosses. 



