B. II Ashley — Dithionic Acid and the Dithionates. 259 



Art. XXV. — The Analysis of Dithionic Acid and the 

 Dithionates ; by R. Harman Ashley. 



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



According to the method of analysis employed by Dymond 

 and Hughes* in the examination of potassium dithionate, 

 obtained by these investigators as a product of the interaction 

 of potassium permanganate and sulphur dioxide, a weighed 

 amount of the dithionate is dissolved in water, the solution is 

 introduced into a partially vacuous closed flask containing 

 hydrochloric acid, and, after heating, iodine is run in to deter- 

 mine the sulphur dioxide. In this action of hydrochloric acid 

 decomposition takes place according to the equations 



BaS,0 6 + 2HCl = H 2 S 2 6 + BaCl 2 

 H 1 S 1 0. = H i S0 4 + S0 1 . 



The sulphur dioxide formed is calculated in accordance with 

 the expression 



S0 2 + I 2 4-2H 2 0=H a S0 4 + 2HI. 



It is to be noted, however, that the procedure of Dymond and 

 Hughes according to which iodine is introduced into the solu- 

 tion of sulphur dioxide was long ago criticized by Finkener,f 

 and for it has been substituted the method suggested by 

 Finkener and elaborated by YolhardJ according to which the 

 solution of sulphur dioxide or the sulphite is introduced 

 slowly from a burette into the iodine solution, the purpose 

 being to obviate the establishment of a secondary reaction 



S0 2 + 4HI = 2H0 2 + S + 2I 2 . 



It seemed desirable therefore to study the decomposition of 

 dithionates by boiling with hydrochloric acid under conditions 

 which would permit the estimation of the evolved sulphur 

 dioxide by bringing it into action in small amounts upon an 

 excess of iodine, in accordance with the principle of the 

 Finkener-Volhard process. 



Barium dithionate was chosen as a suitable salt for investi- 

 gation. It was prepared in the following manner : Manga- 

 nese dioxide suspended in water was treated with sulphur 

 dioxide gas in a vessel surrounded with melting ice. After 

 this treatment the solution was made alkaline with an excess 

 of barium hydroxide to remove sulphates and sulphites as 



* J. Chem. Soc, lxxi, 314-318. 

 f Finkener-Rose, Quant. Anal., vi Auf., p. 837. 

 JAnn. Chem. Pharm., ccxlii, 94. 

 Am. Jour. Sci. — Fourth Series, Vol. XXII, No. 129. — September, 1906. 

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