Ashley — Oxidation of Sulphites by Iodine. 



239 



Excess of Iodine determined by standard arsenite. 



Iodine 



value of 



S0 2 taken. 



Iodine 

 taken. 



Iodine value 



of arsenite 



taken. 



NaHCOs 

 taken. 



Error in 

 terms of 

 Iodine. 



Error in 



terms 



of S0 2 . 



gr. 



gr. 



gr- 



gr. 



gr. 



gr. 



0-0977 

 0-0977 

 0-1440 

 0-1440 

 0-2759 

 0-2759 



0-2495 

 0-2495 

 0-2984 

 0-3017 

 0-4354 

 0-4354 



0-1543 

 0-1540 

 0-1586 

 0-1607 

 0-1710 

 0-1742 





— 00025 



— 0-0022 



— 0-0042 



— 0-0030 



— 0-0115 

 -0-0147 



— 0-0006 



— 0-0006 



—o-ooio 



— 0-0008 



— 0-0029 



— 0-0037 



From a comparison of the results in the second section of 

 the table with those in the first section, it appears that under 

 the conditions advocated by Rupp, the sulphite is not com- 

 pletely oxidized by the iodine. It seems that enough of the 

 secondary action, by which the thiosulphate is oxidized beyond 

 the condition of tetrathionate, takes place to counterbalance 

 the error of incomplete oxidation when moderate amounts of 

 sulphurous acid are handled, and more than enough for the 

 smallest amounts, the secondary error predominating in such 

 cases. 



The results of experiments in which acid potassium carbon- 

 ate was substituted for the acid sodium carbonate gave similar 

 results. 



So it appears that when Rupp's process gives results approx- 

 imating the truth, it is due to the happy balancing of opposed 

 errors. It seems quite possible that the same balancing of 

 errors likewise occurs in the process for the determination of 

 phosphorous acid described by Rupp and Fink.* 



In conclusion, I would like to thank Prof. F. A. Gooch for 

 many kind suggestions. 



*Ber. Dtch. Chem. Ges., xxxv., 3691, 1902. 



