METHODS OP ANALYSIS FOB CERTIFIED COLORS. 211 



absence, is a matter that varies so much from case to case that it must 

 be left largely to the individual judgment to decide on the best com- 

 bination of tests, and for that reason such combinations are not here 

 offered. The general methods and procedures just outlined have, 

 however, when properly combined, led to satisfactory results. 



In order to compare the results of the color analyses on the same 

 basis, the actual figures obtained in the various determinations 

 besides being reported as found, are also recalculated on a basis of 

 100 parts of actual color, i. e., the sum of the percentages of material 

 which is not coloring matter, such as moisture, total insoluble matter, 

 sodium chlorid, sodium sulphate, and ether extractives is deducted 

 from 100 and the percentages of the various constituents found 

 divided by the difference, the quotient being then multiplied by 100. 

 The percentage of sodium in actual dye is calculated from the sul- 

 phated ash. The methods of analysis of the seven permitted colors 

 of Food Inspection Decision No. 76 are given in the following order: 



1. Naphthol Yellow S. 



2. Ponceau 3R. 



3. Orange I. 



5. Light Green S F Yellowish. 



6. Erythrosin. 



7. Indigo Disulphoacid. 



4. Amaranth. 



NAPHTHOL YELLOW S. 

 MOISTURE. 



Dry from 1 to 2 grams of the finely powdered dye in an air oven at 

 120 to 125 C. to constant weight. 



TOTAL INSOLUBLE MATTER. 



Dissolve 5 grams of color in 200 cc of hot distilled water, filter 

 through a tared gooch, wash till the washings run through colorless, 

 dry the insoluble residue at 105 C., and weigh. 



NONVOLATILE OR INORGANIC INSOLUBLE MATTER. 



Ignite the gooch containing the insoluble matter of the last deter- 

 mination at a low red heat, cool, and weigh. 



SODIUM CHLORID. 



Dissolve 3 to 5 grams of dye in 200 cc of water, acidify the solution 

 with nitric acid, and precipitate the chlorin as silver chlorid. The 

 latter is separated, washed, ignited, and weighed in a tared gooch 

 crucible in the usual way. 



SODIUM SULPHATE. 



Dissolve 1 gram of dye in about 100 cc of water in a 200-cc gradu- 

 ated flask, add 40 cc of a 20 per cent solution of potassium chlorid, 

 shake the mixture well, make up to mark with water, shake again, 



