238 



Ashley — Oxidation of Sulphites by Iodine. 



alkaline solution. The sodium thiosulphate, approximately 

 ^5 was standardized against approximately ^ iodine solution 

 in a neutral solution. Varying amounts of a saturated solu- 

 tion of acid sodium carbonate were used to render the solution 

 alkaline in the experiments recorded. 



Table I. 



Iodine solution = 0*01236 gr. per cm 3 . 



Sodium thiosulphate solution = 0-01516 gr. per cm 3 . 





Na 2 S 2 3 nearly— 

 J 10 



Iodine nearly — 

 J 10 



Error in 

 terms of I. 



NaHC0 3 



Treat- 

 ment. 



No. 



cm 3 



I 



value, gr. 



cm 3 



gr. 



gr. 



cm 3 



1. 



2. 

 3. 

 4. 

 5. 

 6. 

 7. 

 8. 

 9. 

 10. 



11-94 

 11-69 

 11-18 

 11-25 

 9-18 

 9*11 

 15-00 

 15-00 

 15-00 

 15-00 



0-1451 



0-1421 



0-1359 



0-1367 



0-1116 



0-1107 



0-1823 

 a 



u 

 a 



15-00 

 15-00 

 15-00 

 15 00 

 11-00 

 11-00 

 15-98 

 16-31 

 16-62 

 16-05 



0*1854 



a 

 a 

 a 



0-1360 



u 



0-1975 

 0-2016 

 0-2054 

 0-2058 



+ 0-0403 

 + 0-0433 

 + 0*0495 

 + 0-0487 

 + 0-0244 

 + 0-0253 

 + 0-0152 

 + 0-0193 

 + 0-0231 

 + 0-0235 



20 

 20 

 40 

 40 



1 gr. 



1 gr. 

 20 

 20 

 40 

 40 



1 



Na 2 S 2 O s 

 ■ into 

 Iodine. 



J 



1 



1 Iodine 

 1- into 

 | Na 2 S 2 3 



J 



It is plainly evident from the table that more iodine is used 

 up in the presence of an alkali bicarbonate, whether the iodine 

 is run into the thiosulphate or the thiosulphate into the iodine, 

 than accords with the theory of the reaction. 



Experiments were now undertaken for the purpose of con- 

 trasting the results obtained by Rupp's procedure with results 

 found by oxidizing the sulphite with iodine in an alkaline 

 solution and determining the excess of iodine by standard 

 arsenite, which, as is well known, acts with regularity upon 

 iodine in the presence of an acid sodium carbonate. The 

 volumes of the solutions at the time of oxidation varied from 

 25 cm3 to 50 cm3 . The results are given in the following table : 



Table II. 

 Eupp's Procedure. 



Iodine 



value of 



S0 2 taken. 



Iodine 

 taken. 



Iodine value 



of Na 2 S 2 3 



taken. 



NaHC0 3 

 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 



0-2474 

 0-2474 

 0-2969 

 0-2969 

 0-4316 

 0-4316 



0-1492 

 0-1454 

 0-1528 

 0-1518 

 0-1582 

 0-1628 





+ 0-0005 

 + 0-0043 

 + 0*0001 

 + 0-0011 



— 0-0025 



— 0-0071 



+ 0-0001. 

 + 0-0011 

 + 0-0000 

 + 0*0003 



— 0-0006 



— 0-0018 



