R. H. Ashley — Dithionic Acid and the Dithionates. 261 











Table I. 









Decomposition of barium dithionate 



by boiling with hydrochloric 



acid. 







I value 



I value of 





Errors 



Errors 







S 2 5 



Of S a 8 



I Na 2 S 2 3 



S 2 5 



in 



in 





, 



taken. 



taken. 



taken, required. 



found. 



I. 



S 2 5 . 



Time. 



No. 



grm. 



grm. 



grm. 



grm. 



grm. 



grm. 



grm. 



min. 



1 



•0854 



•1898 



•5721 



•3782 



•0872 



+ •0041 



+ •0018 



90 



2 



•1298 



•2885 



•5846 



•2920 



•1316 



+ •0041 



+ •0018 



90 



3 



•1429 



•3177 



•5778 



•2007 



•1426 



— •0006 



— •0003 



45 



4 



•1042 



•2317 



•5765 



•3468 



•1033 



— •0020 



— •0009 



60 



5 



•1031 



•2293 



•5884 



•3557 



•1047 



+ •0034 



+ •0016 



00 



6 



•0704 



•1564 



•5751 



•4228 



•0685 



-•0041 



— •0019 



60 



7 



•0778 



•1729 



•6194 



•4637 



•0700 



— •0172 



— •0078 



60 



8 



•1043 



•2319 



•5726 



•3395 



•1048 



+ •0012 



+ •0005 



30 



9 



•1043 



•2319 



•5892 



•3548 



•1054 



+ •0025 



+ •0011 



60 



10 



•1042 



•2317 



•6110 



•3849 



•1017 



— •0056 



— •0025 



105 



The irregularity of these results may conceivably be due to 

 one or more of three different reasons. In the first place, it 

 may be that the decomposition of the dithionic acid is not 

 complete, and that this may be so is shown by the fact that 

 after the liquid in experiment 10 was boiled for an hour and 

 three quarters and filtered from the precipitated barium sul- 

 phate, the addition of sulphuric acid caused further precipi- 

 tation of barium sulphate. Secondly, it may be that some of 

 the sulphur dioxide escapes absorption in the receiver if the 

 current of carbon dioxide is passed through the system too 

 rapidly. Thirdly, the concentration of the hydrochloric acid 

 in the receiver tends, as is well known, to render the titration 

 of the residual iodine by sodium thiosulphate less exact and 

 the starch iodide less delicate as an indicator. 



To eliminate the concentration of acid in the receiver, in 

 the following experiments sulphuric acid was substituted for 

 hydrochloric acid in the Yoit flask. A weighed amount of 

 barium dithionate was introduced into the Yoit flask and 

 there dissolved in water. Sulphuric acid was run in through 

 the separating funnel and the mixture then boiled, the sul- 

 phur dioxide being collected in the Drexel receiver, trapped 

 as before with potassium iodide. A slow current of carbon 

 dioxide w T as driven through the system to sweep the sulphur 

 dioxide into the iodine and to prevent any sucking back. 

 When boiling had been carried so far that fumes of sulphuric 

 acid began to appear the operation was stopped and the excess 

 of iodine remaining was determined by means of sodium 

 thiosulphate, starch iodide being used as an indicator. 

 Results of experiments carried out in this manner are given 

 in Table II. 



