372 MESSRS. V. H. VELEY AND J. J. MANLEY ON 



of the above .writers has been criticised by KUSLER,* who found by an electric 

 resistance method that a saturated solution of barium sulphate in water contains 

 1 part of salt in 425,000 water (equals 2'35 parts per million), a result in accordance 

 with the former observations of ROSE, KOHLRA.USCH, and HOLLEMANN. 



In the estimation of the amount of impurity of sulphuric acid in the samples used, 

 1 cub. centim. of a 10 per cent, solution of barium nitrate was added to 10 cub. centhns. 

 of the nitric acid, which had been neutralised previously by a solution of ammonia ; 

 the quantity of the barium niti'ate was more than a hundredfold in excess of that 

 required to precipitate the greatest amount of sulphuric acid likely to be present. In 

 a blank experiment with water which had been distilled over baryta it was found that 

 2 - 3 parts of sulphuric acid per million water produced a turbidity with the barium 

 nitrate ; but in the case of a sample of nitric acid of 50 per cent, concentration, after 

 neutralisation with ammonia, 2'8 parts of sulphuric acid per million produced a 

 turbidity. The mean of these two numbers, namely 2'5, may reasonably be taken as 

 the limit of delicacy of the reaction within the limit of '0650 per cent. ; from the 

 results calculated upon this basis the greatest quantity of sulphuric acid found was 

 4'3 parts per million. A selection is given below (p. 385) of various acids used in order 

 to show the degree of purity attained. 



DETERMINATION OF THE CONCENTRATION OF THE SOLUTIONS. 



For this purpose standard solutions of sodium hydrate were made from metallic 

 sodium, purified by melting it in vacuo and filtering the molten metal through iron 

 gauze ; it was then placed in a silver dish and allowed to hydrate slowly in the vapour 

 of water from a dilute soda solution ; the method adopted has previously been fully 

 described. 



The solution thus obtained was made up to a definite volume and standardised as 

 against (i.) sulphuric and (ii.) hydrochloric acid ; the acidity of the former was deter- 

 mined volumetrically by sodium carbonate, and gravimetrically as barium sulphate, 

 that of the latter (i.) volumetrically by pure metallic silver, by the method of STAS, 

 and (ii.) volumetrically by sodium carbonate. Three different methods and two 

 different indicators, namely, litmus and methyl-orange, were used by two different 

 individuals. The degree of concordance obtained for one such standard solution of soda 

 is shown by the following table : 



' Zeits. Anorgan. Cbem.,' vol. 112, p. 261. 



