Jamieson — Polytli ion ic A c ids. 



639 



Art. XLIY. — The Volumetric Determination of Poly th ionic 

 Acids by Potassium Iodate ; by George S. Jamieson. 



In a recent paper* from tins laboratory it was shown that 

 sulphurous acid could be titrated with a solution of potassium 

 iodate in the presence of 15 to 20 per cent of actual hydro- 

 chloric acid and a small volume of an immiscible solvent, such 

 as chloroform, according to the general method of L. W. 

 Andrews.-)* It has been found that thiosulphuric and tetra- 

 thionic acids can be titrated in the same manner, while 

 dithionic acid on account of its stability cannot be determined 

 by this method. 



In order to test the method for the titration of thiosulphates, a 

 solution containing 3*567 g. of normal potassium iodate in 

 1000 cc was used4 According to the equation of the reaction 

 2KI0 3 + Na 2 S 2 3 .5H 2 + 2HC1 = Na 2 S0 4 + K 2 S0 4 + 2IC1 + 

 6H 2 l cc = -002068 g. of Na 2 S 2 3 .5H 2 0. The titrations were 

 made in glass stoppered bottles in exactly the same manner as 

 in the determination of sulphurous acid. It is important to 

 titrate as soon as possible after the thiosulphate is brought in 

 contact with the hydrochloric acid, which should not be warmer 

 than 18° C. Also it is best to dissolve the thiosulphate in a 

 little water previous to adding the hydrochloric acid. For 

 convenience several solutions of sodium thiosulphate of various 

 strengths were prepared and standardized by titration with 

 known amounts of pure iodine in the usual manner, observing 

 all precautions. 



The following results were obtained : 



No. 



1 



2 

 3 



4 

 5 

 6 



7 

 8 



Na 2 S 2 3 .5H 2 

 taken 



•0506 

 •0758 

 •1210 

 •1011 

 •0603 

 •0253 

 •0506 

 •0253 



ccKI0 3 

 used 



24-4 

 36-6 

 58*5 

 48-7 

 29-4 

 12'3 

 24-5 

 12-2 



Na 2 S 2 3 .5H 2 

 found 



•0505 

 •0757 

 •1208 

 •1007 

 •0607 

 •0253 

 •0507 

 •0252 



Error 



— '0001 



— '0001 



— -0002 



— '0004 

 + -0004 



•0000 



+ -oooi 



— -0001 



The titrations given in the table below were made with a 

 potassium iodate solution which had the value l cc = 005300 g. 

 of Na 2 S,0 8 .5H 2 0. 



* This Journal, xxxviii. 166. 1914. 

 f Jour. Amer. Chem. Soc, 25, 756, 1903. 



X This solution was previously used for the determination of sulphurous 

 acid mentioned above. 



