*- 



Issued December 19, 1910. 



United States Department of Agriculture, 



BUREAU OF CHEMISTRY Circular No. 65. 

 H. W. WILEY, Chief of Bureau. 



THE ESTIMATION OF IODIN IN ORGANIC COMPOUNDS AND ITS 

 SEPARATION FROM OTHER HALOGENS. 



By A. F. SEEKER and W. E. MATHEWSOX, 

 Assistant chemists, Ntw York Food and Drug Inspection Laboratory. 



In the examination of a number of samples of commercial eryth- 

 rosin the determination of iodin was considered to be one of the most 

 important factors in establishing the identity and purity of the 

 dye. As many of the colors contained varying amounts of common 

 salt, and contamination with chlorin and bromin substitution prod- 

 ucts of fluorescein was also to be sought and detected, the problem 

 of estimating iodin under these conditions by a method that would 

 not require a prohibitive amount of manipulation and time pre- 

 sented itself. At first an attempt was made to estimate the total 

 halogens by the Carius method, from which the' halogen due to 

 common salt (estimated in another portion after separation of the 

 color acid) was deducted. A qualitative test for chlorin and bromin 

 in the residue left after ignition of the color acid with alkali was 

 relied upon to detect these halogens in organic combination. 



The Carius method was found to yield erratic and unreliable 

 results with erythrosin, confirming the experience of other analysts 

 with iodin compounds. Linnemann ascribed the difficulty to the 

 solubility of silver iodid in nitric acid containing an excess of silver 

 nitrate. The authors have observed crystals of free iodin in the bomb 

 tubes after removal from the furnace, and on heating they were seen 

 to volatilize with the formation of the characteristic violet vapors. 

 An ample excess of silver nitrate over that requii;ed for the iodin 

 present had been added in every case. As the results of the deter- 

 minations by the Carius method were almost invariably too low, it 

 U the opinion of the authors that some of this free iodin is lost in 

 transferring the oxidizing mixture from the bomb tubes. 



Ann. Chem. Pharm. 1371, 160: 205. 

 66119 Cir. 6510 



277610 



