260 jR. II Ashley — Dithionic Acid and the Dithionates. 



well as to convert the manganese dithionate to barium dithion- 

 ate. The excess of barium hydroxide was removed by intro- 

 ducing carbon dioxide and boiling to break up any acid barium 

 carbonate which might have been formed and the solution was 

 filtered. The filtrate from the barium carbonate contained 

 pure barium dithionate, which was obtained in solid form by 

 evaporating this solution. 



The salt so prepared gave all the reactions of dithionic 

 acid and had a composition corresponding to the formula 

 BaS 2 6 # 2H 2 0. In determining the composition of the salt two 

 methods were used. In the first, the barium was precipitated 

 by sulphuric acid and weighed as barium sulphate ; in the 

 second method the salt was introduced into a platinum cruci- 

 ble and blasted to drive off water and sulphur dioxide, the 

 residue being weighed as barium sulphate. 



A salt of the formula Ba$ 2 6 '4H 2 is said to be formed by 

 slow evaporation.* According to my experience, however, 

 the salt crystallized by evaporation over a flame and that by 

 evaporation at the ordinary temperature in a vacuum 'over 

 concentrated sulphuric acid had the same composition and 

 both preparations gave on analysis figures corresponding to 

 the formula Ba$ 2 6 *2H 2 0, the results coming within 0*3 per 

 cent of theory. Crystals of barium dithionate are supposed 

 to effloresce, but no evidence of such action was found in my 

 preparations when the crystals were kept in a weighing 

 bottle at ordinary room temperature. 



In studying the decomposition of barium dithionate under 

 the action of hydrochloric acid, crystals of the salt were 

 weighed out and transferred into a Yoit flask provided with a 

 separating funnel sealed on. The outlet was connected to a 

 Drexel receiver containing a known amount of standardized 

 iodine, and the outlet of this receiver was provided with a 

 trap containing a solution of potassium iodide. Water was 

 first run into the Yoit flask through the separating funnel and 

 the salt was dissolved by the aid of heat. Acid was next run 

 in through the separating funnel and the whole was boiled, a 

 current of carbon dioxide being employed to sweep the sul- 

 phur dioxide into the iodine. Hydrochloric acid was added 

 from time to time through the separating funnel to keep up 

 the volume of the liquid and the concentration of the acid. 

 After the operation had proceeded for the times noted, the 

 whole was disconnected and the iodine remaining was deter- 

 mined by means of sodium thiosulphate with starch as an 

 indicator. Results of experiments conducted in this manner 

 are given in Table I. 



* Watt's Diet., vol. iv, p. 696. 



