62 



NOTES ON THE ANALYTICAL SCHEME. 



In the preparation of the analytical scheme, the strength of aqueous 

 solutions of coloring matters is approximately 0.01 per cent in the 

 case of coal-tar colors and 0.1 per cent in the case of natural coloring 

 matters. 



The following reagents are used and of the strength described, 

 unless otherwise specified: 



Tannin reagent. As recommended by Weingartner, 10 grams each 

 of tannic acid and sodium acetate in 100 cc of water. 



Hydrochloric acid. Mix equal volumes of concentrated acid and 

 water. 



Sodium hydrate solution. Ten grams in 100 cc of water. 



Ammonia solution. Approximately 10 per cent NH 3 in water. 



Lead subacetate solution. Specific gravity 1.25. (See Chemistry 

 Bulletin 107, p. 40.) 



Normal lead acetate solution. Ten grams in 100 cc of water. 



Keactions in aqueous or alcoholic solution are carried out by adding 

 to 10 cc of color solution 5 to 10 drops of reagent. 



Unless otherwise noted, each test is to be made on a part of the 

 original color solution and not on the solution used for the previous 

 test. 



To determine whether a large amount or almost no color is extracted 

 by immiscible solvents is not always very easy by simple inspection, 

 and it is then best to separate the immiscible solvent from the aqueous 

 layer, filter the former, and evaporate it on the water bath with the 

 addition of water if necessary, as in the case of amyl alcohol. Take 

 up the color in water, make slightly acid or alkaline, according to 

 whether the aqueous layer was acid or alkaline, and compare with the 

 latter. Any considerable amount of color will then be more readily 

 evident, and the dye could also be fixed on wool, which it should 

 color strongly. 



If the solution is decolorized by acid or alkali when shaking with an 

 immiscible solvent, it is necessary to separate the two layers carefully 

 and neutralize both in order to find the relative proportion of color 

 in each layer. 



In all cases it is advisable, after using the analytical scheme for the 

 identification of a color, to confirm its identity further by applying 

 the appropriate tests as given in Tables I to IV. Many special tests 

 for certain colors will also be found in Allen, loc. cit. ; Girard, Analyse 

 des matieres alimentaires, etc.; Circular 25 and Bulletin 107, Revised, 

 Bureau of Chemistry; and other works. 



Acknowledgment is made of the assistance of F. F. Flanders in the 

 testing of the analytical scheme and of valuable suggestions from 

 B. C. Hesse, New York City, and R. F. Hare, Agricultural College, 

 New Mexico. 



[Cir. 63] 



