A nu'mbe'r : )f.'metlid(j[?;l\av/3,'been suggested for the estimation of 

 iodin in the presence of other halogens in inorganic soluble com- 

 pounds. Those involving the conversion of iodid into iodate by 

 potassium permanganate have been described by Reinige 6 and by 

 Baubigny and Rivals. The application of these and of most other 

 methods requires a preliminary destruction of the organic matter, 

 and this, if accomplished in the usual way by fusion with potassium 

 carbonate or a similar alkaline substance, requires much care, and 

 in the case of mixtures containing sulphonated dyes, yields a melt 

 which contains reducing sulphur compounds. These compounds 

 must be removed before the application of Reinige's method, which 

 is also subject to the limitations of volumetric processes in general. 

 With Baubigny's method the distillation requires close attention and 

 much difficulty was experienced in driving off all chlorin without 

 loss of iodin. 



Experiments proved that if a solution containing erythrosin is 

 treated with potassium permanganate and nitric acid the organic 

 matter is completely decomposed and chlorin and bromin are con- 

 verted into volatile products, while all of the iodin remains as iodic 

 acid. The permanganate is converted into a voluminous hydrated 

 oxid of manganese. The chlorin apparently is partly liberated as 

 such and partly converted into an oxygenated compound which is 

 boiled off with difficulty, but may be volatilized in a current of 

 steam or driven off by evaporating the mixture to dryness on a 

 steam bath. When much chlorin is present the last of it can be 

 removed only by treating the residue twice with nitric acid and 

 again evaporating to dryness. That no iodin is lost in this process 

 is shown in Table 1. Iodin may be determined in the residue left 

 after oxidation by the permanganate by taking up in a little water, 

 adding nitric acid, and then dissolving the oxid of manganese in an 

 excess of sulphur dioxid solution, the iodic acid being at the same 

 time reduced. Silver nitrate is added to the clear solution, which 

 is then boiled until the excess of sulphur dioxid is driven off and the 

 silver iodid has coagulated. This is filtered, washed, dried, and 

 weighed in the usual manner. 



The experimental results given in Table 1 were obtained on mix- 

 tures containing measured amounts of a solution of pure iodin. To 

 prepare this, resublimed iodin was dissolved in a concentrated solu- 

 tion of potassium iodid and a large part of it then precipitated by 

 the addition of water. The precipitated portion was collected on 

 a perforated plate, thoroughly washed with water, and sublimed. 

 The sublimate was dried over calcium chlorid. Portions of this 



aHempel, Ann. Chem. Pharm. 1858, 107: 100. 

 &Zts. anal. chem. 1870, ff: 39. 

 c Compt. rend. 1903, 137: 927. 

 Cir. 65 



