166 G. S. Jdmieson — New Volumetric Method . 



Art. XVI. — A New Volumetric Method for the Determina- 

 tion of Sulphurous Acid ; by George S. Jamieson. 



Most of the methods for the determination of sulphurous 

 acid, either free or combined, have been based upon iodometric 

 processes. The difficulties formerly encountered in the iodo- 

 metric analysis of these substances have been overcome bv the 

 modification of Giles and Shearer,* which consists in adding 

 the sulphurous acid or sulphite to a measured excess of N/10 

 iodine solution and titrating the unaltered iodine with N/10 

 sodium thiosulphate solution. 



The method to be described is based upon the titration of 

 sulphurous acid with potassium iodate in the presence of 15 to 

 20 per cent of actual hydrochloric acid and a small volume of 

 an immiscible solvent such as chloroform. This general 

 method of titration is the well known one of L. W. Andre\vs,+ 

 but as far as is known it has not been applied previously to the 

 titration of sulphurous acid. The method is especially adapted 

 for use with solutions, although it is possible to titrate sulphites 

 without previous solution as shown beyond. It has the advan- 

 tage over the iodometric method in requiring only a single 

 very stable volumetric solution instead of two solutions which 

 cannot be preserved for a long time unchanged. 



In order to test the method, a solution containing 3*567 

 grams of normal potassium iodate in a 1000 cc was prepared. 

 According to the equation of the expected reaction 



KI0 3 + 2H 2 S0 3 4- 2HC1= 2H 2 S0 4 + IC1 + KCI + H 2 



the equivalent of this solution is l cc = -002135g. of S0 2 . 



The potassium iodate solution was standardized with pure 

 resublimed iodine under the same conditions as described 

 beyond for the titration of sulphurous acid. 



No. 

 I 



II 

 Average 



Since the reaction in the case of the iodine is represented by 

 the equation 



4I + KI0 3 + 6HC1 = KCI + 51C1 + 311,0 



the strength of the potassium iodate solution was l cc = 

 •002135g. SO.,. The titrations were carried out in a glass 

 stoppered bottle of 250 cc capacity in the presence of a cooled 



* J. Soc. Chem. Ind., iii, 197, and iv. 303. 

 f Journ. Amer. Chem. Soc, xxv, 756, 1903. 



% Stronger solutions can be used to advantage when comparatively large 

 amounts of sulphurous acid are to be titrated. 



ine taken 



KIO3 used 



Wt. of I for 1- 



•4261 



50'55 cc 



•00845 



•2024 



23-90 



•00847 

 •00846 



