3.36 MR. W. C. P. WHETHAM ON THE IONIZATION OP 



%S5 gramme of water was then added from the filling machine. 



12.50 -12 34010 



12.55 -13 33920 



1.10 '18 33750 



Considering that the resistance of the solvent only comes in as a correction of the 

 observed resistances of the solutions, the slight change, if any, which these figures 

 show is quite negligible. 



SECTION 7. On the Preparation of the Water. 



Great difficulties occurred in getting water of quality good enough for the experi- 

 ments. The process finally adopted was as follows : Tap water was boiled tb pre- 

 cipitate calcium carbonate, and filtered through paper. It was mixed with potash 

 and potassium permanganate till the colour became a deep purple, and then distilled 

 from a copper still. The water (No. 1) so obtained was redistilled from a big Jena glass 

 flask with a much smaller quantity of alkaline permanganate. The product (No. 2) 

 of this operation was placed in a large platinum still, a very small quantity of acid 

 potassium sulphate was added, and the water (No. 3) was slowly collected in platinum 

 vessels. The platinum still stood on a screen of sheet copper in order to shield it 

 from the products of combustion of the gas burner. In all the distillations the first 

 and last portions of water obtained were rejected, together about one-third of the 

 whole. The water thus prepared, when measured in the platinum cell at 18, had 

 an average conductivity of about '9 X 10~ 15 C.G.S. unit. The best water obtained 

 by KOHLRAUSCH* by distillation in air had a conductivity at the same temperature of 

 '7 X 10~ 16 , while by distilling in vacuo a value as low as '2 X 10~ 15 was reached, t 



SECTION 8. On the Preparation of the Stock Solutions. 



Miss D. MARSHALL was good enough to prepare some of the stock solutions for 

 the early part of the work, and Mr. H. J. H. FENTON kindly allowed most of those 

 used in the later experiments to be made up under his advice by Mr. GEORGE HALL, 

 at the Cambridge University Chemical Laboratory. Details of the methods are given 

 in Section 11, under the heading of each substance. The concentration of these 

 solutions was in general about one-third to one-half normal. They were made up 

 and kept in Jena gkss flasks accurately stoppered. Glass is less soluble in salt and 

 acid solutions than in pure water, and, under any circumstances, the small quantities 



* Kohlrausch und Holborn, ' Leitvermogen der Electrolyte,' p. 111. 

 t Kohlrausch und Heydweiller, ' Wied. Ann.,' vol. 53, p. 209, 1894. 



