242 Conductivity of Aqueous Solutions. Part VIII. 



chloric acid, dried, dissolved in boiling water, and crystallized at 5. 

 The crystals were washed and dried. A second sample was obtained by 

 adding hydrochloric acid to the mother liquor from these crystals. No 

 difference was noticed in the conductances of these two lots. In making 

 standard solutions this substance was freshly ignited almost to the fusing 

 point, weighed out, and dissolved in a graduated flask. 



Sodium chloride was also used for determining the conductance-capac- 

 ity. This was purified by twice precipitating Kahlbaum's "chemically 

 pure" product with hydrochloric acid. The final precipitate was dried 

 and gently ignited. 



The stock sulphuric acid solution used for all the measurements was a 

 fifth-normal one prepared by Mr. Y. Kato on August 10, 1905, by dilut- 

 ing with conductivity water a sample of the "strictly chemically pure 

 sulphuric acid" furnished by Baker and Adamson. The concentrated 

 acid (usually 10 c.cm. portions) was tested by him for arsenic with hydro- 

 gen sulphide, for nitric acid with diphenylamine, for nitrous acid with 

 starch and potassium iodide, for hydrochloric acid with silver nitrate, for 

 selenium with ferrous sulphate, and for ammonia with Nessler solution. 

 None of these impurities was present in appreciable quantity, if at all. 

 The concentration of the solution was determined on August 11-15, 1905, 

 both by precipitating and weighing the acid as BaS0 4 and by titration 

 with phenolphthalein against a hydrochloric acid solution previously 

 standardized by weighing the AgCl yielded by it. The sulphuric acid 

 was restandardized on December 9, 1905, against an ignited sample of 

 sodium carbonate furnished with an analysis showing substantial purity 

 by J. T. Baker.* To the solution of a known weight of the carbonate, 

 a slight excess of the stock sulphuric acid was added, the solution boiled 

 for ten minutes and then titrated with 0.01 normal potassium hydroxide 

 with the help of phenolphthalein as an indicator. 



We are indebted to Mr. G. A. Abbott for the preparation and analysis 

 of the stock solution of phosphoric acid which was used in this part of the 

 investigation. This sample of acid was prepared by Mr. Abbott by direct 

 oxidation of yellow phosphorus. The method is summarized as follows : 

 Carefully selected clean pieces were heated in a retort with nitric acid 

 (sp. gr. 1.20). After the phosphorus had disappeared the contents of 

 the retort were evaporated in small portions with addition of enough nitric 

 acid to insure complete oxidation of any phosphorous acid until the white 



*The BaSOi determinations gave for the concentration, expressed in millimols 

 H2SO4 in a kilogram of solution, 110.54, 110.51, and 110.52, from which by correcting 

 the weighings to vacuo, the value 110.43 results. The atomic weights used were 

 = 16.00, Ba = 137.4, S = 32.06, and H = 1.01. By the titration against the hydro- 

 chloric acid the value 110.70 was obtained ; and from that against sodium carbonate 

 110.71 resulted. The mean 110.61 was adopted. 



