METHODS OF ANALYSIS FOR CERTIFIED COLORS. 223 



his modification of the Gutzeit test. See under Naphthol Yellow S, 

 pages 212 and 213. (NOTE. It is somewhat difficult at times to 

 recover 250 cc of filtrate, but less may be used and a correction made, 

 if necessary.) 



ETHER EXTRACTIVES. 



Determine as given under Naphthol Yellow S, page 214, omitting 

 the acid extraction. 



SULPHATED ASH. 



Determine as given under Naphthol Yellow S, page 214. 



IODIN, BROMIN, AND CHLORIN (CORNELISON*S METHOD). 



Mix 0.2 to 0.3 gram of the sample with 2 grams of pure potassium 

 bichromate and 15 cc of strong sulphuric acid hi the evolution flask 

 of an apparatus made entirely of glass, with ground-glass joints. 

 Thoroughly mix the contents of the evolution flask, so that all lumps 

 are disintegrated, and then heat at 100 C. for 15 minutes, after 

 which raise the temperature to 150 C. for thirty minutes, a cur- 

 rent of air dried over calcium chlorid and potassium hydroxid being 

 drawn through the apparatus during this time. lodin remains hi 

 the evolution flask as iodic acid; bromin passes off as such, and may 

 be absorbed by allowing the air passing through the apparatus to 

 bubble through 1 per cent sodium hydroxid. Chlorin passes out of 

 the evolution flask as chromyl chlorid, and may also be absorbed in 

 sodium hydroxid. Cool the mixture containing the iodic acid, and 

 reduce the chromic acid by addition of sulphur dioxid, about 20 cc 

 of a saturated solution being required. When enough has been 

 added, the precipitated iodin redissolves, and the clear green color 

 of chrome alum appears. Filter, wash the paper with distilled water, 

 dilute the filtrate and washings to about 300 cc, and add an excess of 

 silver nitrate. Boil till the silver iodid has flocculated, allow to stand 

 for a few hours, and separate and weigh the silver iodid in a tared 

 gooch. 



It sometimes happens that the mixture containing the iodic acid, 

 after the reduction with sulphur dioxid, becomes turbid, owing, 

 apparently, to separation of a basic chromium sulphate. Very often 

 the turbidity can not be removed by filtering, and it has been found 

 advisable in this case to reject the determination and begin anew. 



IODIN (SEEKER AND MATHEWSON'S METHOD). 1 



Place from 0.3 to 0.4 gram of the erythrosin in a porcelain casserol, 

 dissolve this in 5 cc of a 10 per cent sodium hydroxid solution, then 

 add 35 cc of a 7 per cent solution of potassium permanganate. After 



U. S. Dept. Agr., Bureau of Chemistry, Circular 65. The estimation of iodin in organic compounds 

 and its separation from other halogens. 



