manganate and 5 cc of concentrated nitric acid and again evap- 

 orate to dryness. Then add about 50 cc of water and 5 cc of con- 

 centrated nitric acid to the residue, following this by 40 cc of a 

 saturated solution of sulphur dioxid, and allow the whole to stand 

 with occasional stirring (breaking up the lumps with a glass rod) 

 until the hydrated oxid of manganese has dissolved. Add an excess 

 of silver nitrate to the clear solution, and boil until sulphur dioxid 

 has been expelled and the silver iodid has flocculated. Filter this 

 and weigh in the usual manner. The results obtained are given in 

 Table 2. 



TABLE 2. Estimation ofiodin in erythrosin color add. a 



(Theory 60.75 per cent.) 



a The erythrosin color acid used in these estimations was air dry. 



This procedure was applied to a number of commercial samples 

 containing erythrosin in admixture with ponceau 3R and with 

 amaranth, and in all cases a complete destruction of the organic 

 matter and closely agreeing results were obtained. 



It is believed that this method, with suitable modifications, is 

 applicable to a number of other iodin compounds beside erythrosin, 

 though detailed data substantiating this point have not yet been 

 obtained. Iodin was determined in recrystallized iodoform by first 

 saponifying with alcoholic potash in a pressure flask, evaporating 

 the alcohol, and oxidizing the residue with permanganate as already 

 given. The results are given in Table 3. This procedure may be 

 adopted with the class of compounds that are volatile and easily 

 saponified, but obviously it need only be employed in cases where 

 halogens other than iodin are also present. 



Phenyl iodid, as a representative of another water insoluble class, 

 was heated with the oxidizing mixture in an acetylization flask, the 

 reaction mixture being in this case introduced through the tube of the 

 reflux condenser and boiled until the oily drops of phenyl iodid ceased 

 to appear in the condenser, and then for some time longer, rinsing the 

 condenser from time to time with a few cubic centimeters of the 



Cir. 65 



