W. A. Turner — Sulphur in Soluble Sulphates. 41 



Art. IV. — An Improvement of the Barium Sulphate Deter- 

 mination of Sulphur in Soluble Sulphates when Sodium 

 Salts are Present ; by W. A. Turner. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — cclviii.] 



When barium sulphate is precipitated by the reaction between 

 a soluble barium salt and a soluble alkali sulphate, or in presence 

 of large quantities of alkali salts, there is likely to be, as is well 

 known, considerable contamination of the precipitate. Alkali 

 sulphates and barium chloride may be found in the ignited sul- 

 phate, while hydrochloric and sulphuric acids may be volatilized 

 in the ignition.* If the precipitation is made with the object 

 of determining barium, the ignited precipitate may be dissolved 

 in hot concentrated sulphuric acid, recovered in crystalline 

 form by evaporation of the sulphuric acid, filtered, washed free 

 from impurities, ignited and weighed in a satisfactory condition 

 of purity.f The precipitate formed by an excess of barium 

 chloride, for the purpose of determining the sulphate ion, and 

 contaminated by that reagent, cannot, however, be purified by 

 recrystallization from sulphuric acid since, in this action, the 

 included barium chloride is converted to barium sulphate and 

 added to the amount which represents the sulphate ion to be 

 determined. The magnitude of the error encountered is largely 

 dependent upon the conditions under which the determination 

 is made. While the method may be modified so as to reduce 

 one source of error to a minimum, the Same modification may 

 increase another source of error so that the final result is not 

 satisfactory. In an exhaustive study of the sources of error 

 and the influence of various factors on them, Allen and John- 

 ston and Johnston and Adams (loc. cit.) find no method of 

 eliminating the observed phenomena, but by making a series 

 of corrections are able to derive results which are accurate, or 

 nearly accurate. 



The investigation of which this paper is an account was 

 directed to the elimination of error, due to the incomplete forma- 

 tion of the insoluble barium sulphate, by removing the alkali 

 salts in a preliminary treatment with hydrochloric acid. 



It appeared in preliminary experimentation that the deter- 

 mination of the sulphate ion of pure copper sulphate by pre- 

 cipitating with barium chloride, added (as is usual) in dilute 

 solution and gradually to the hot solution of the copper salt, 

 yields results very near the theory — the tendency of the barium 



*Hulett and Duschak, Zs. anorg. Chem., xl, 196, 1904; Allen and John- 

 ston, Jour. Am. Chem. Soc, xxxii, 588, 1910; Johnston and Adams, ibid., 

 xxxiii, 829. 1911. 



fMar, this Journal (3), xli, 288, 1891; Gooch and Hill, ibid. (4), xxxv, 311, 

 1913. 



