804 EXPERIMENT STATION RECORD. [Vrt. 35 



For the det«*mination of iodin a number of methods were tested. 



The experimental procedures and data obtained are described in detail. 



A new method for the volumetric determination of thiosulphate in the 

 presence of sulphid and notes on the determination of thiosulphate in the 

 presence of sulphite, bisulphite, and sulphid, A. Sandee {Chem. Ztg., 39 

 (1915), No. 148-149, pp. 945-947).— Three articles are presented. 



I. Thiosulphnte in the presence of sulphid (p. 945). — A new procedure based 

 on the following equations, and which depends on titrating the hydrochloric 

 acid formed, is described in detaU : 



3HgCU+2Na=S=4NaCl+ (2HgS.HgCl=) . 

 2Na2S,03+3HgCl2+2H=0=2Na2S04+4HCl+ (2HgS.HgCl2) . 



The total thiosulphate+sulphid content is determined in an aliquot by 

 titration with iodin. A second aliquot is treated with an excess of mercuric 

 chlorid and well shaken until the dark precipitate becomes pure white. Am- 

 monium chlorid is then added and the acid formed titrated with tenth-normal 

 sodium hydroxid and methyl orange as an indicator. 



II. Thio':ylphate in the presence of sulphite (pp. 945. 946). — Earlier methods 

 are briefly reviewed and criticized. The author obtained satisfactory results 

 with the procedure of Bodnar (E. S. R., 31, p. 15), but indicatas that it 

 requires too much time for routine work. The determination of total sulphite-f- 

 thiosulphate by titration with iodin in an aliquot and the titration of the 

 hydrochloric acid formed after treatment with mercuric chlorid in another 

 aliquot is recommended as an accurate and rapid procedure. 



III. Thiosulphate in the presence of sulphid and sulphite (pp. 946, 947). — 

 Previous work is briefly reviewed and the following procedure outlined : 



From 10 to 20 cc. of the sample for analysis is poured into a measured 

 volume of tenth-normal iodin which has previously been acidified with from 

 5 to 10 cc. of tenth-normal hydrochloric acid, the excess iodin is titrated with 

 tenth-normal thiosulphate, and the total sulphid+sulphite-fthiosulphate (a) 

 thus determined. In the same solution the iodin used by the sulphite is deter- 

 mined by titrating the hydrochloric acid formed with standard alkali (b), 

 using methyl orange as indicator, due allowance being made for the hydro- 

 chloric acid previously added. Another portion of the sample is poured into 

 an excess of mercuric chlorid, thoroughly shaken until the dark precipitate first 

 formed becomes pure white, ammonium chlorid added, and the hydrochloric 

 acid formed titrated with tenth-normal sodium hydroxid, using methyl orange. 

 The reactions taking place are those noted above for the sulphid and thiosul- 

 phate and the following for the sulphite : 



Na2S03+HgCl==NaCl-fClHg.S03Na. 



In the thiosulphate reaction two molecular equivalents of hydrochloric acid 

 are liberated by one molecular equivalent of thiosulphate, so that twice the 

 volume of alkali (c) will be necessary for neutralization, as iodin was used in 

 the first titration for thiosulphate. The various components are calculated from 



data as follows: Iodin used for thiosulphate^-^ ; for sulphite, b; and for sul- 

 phid, a-(b+-n). It is indicated that a determination can be made in 10 min- 

 utes and that the method is applicable in the presence of carbonate. In this 

 case, however, a further titration with standard acid and methyl orange is 

 necessary. Comparative experimental data demonstrating the accuracy of the 

 method are submitted. 



