ANALYSIS OF PERMITTED COLORS, 1907. 179 



XIV. CHEMICAL EXAMINATION OF THE SEVEN PERMITTED 



COLORS, 1907. 



NEED OF CHEMICAL CONTROL. 



The most striking thing, from the chemist's point of view, in the 

 literature relative to the physiological action of coal-tar colors, is 

 the almost universal absence of the results of chemical examination or 

 identification of the materials subjected to physiological test. There 

 is hardly any description or statement of the strength or the con- 

 centration of the materials examined, or of the amount or nature of 

 materials not coloring matter present in the substances subjected 

 to these physiological tests. It is true that some publications give 

 identification tests, but few assert the identity of the material 

 subjected to certain physiological tests, with the description so given. 



The need for some such chemical control as to identity and quality 

 must be apparent to all having experience with the commercial 

 varieties or grades of coal-tar colors. Many of these commercial 

 brands of coal-tar colors contain added coloring matter other than 

 the principal constituent for the purpose of correcting some defect 

 unavoidably arising during the manufacture. Where those com- 

 mercial brands are sold for textile and other manufacturing purposes 

 there is no valid objection to such practice, because in such uses the 

 tinctorial properties and effects of the commercial brands are the things 

 the buyers desire and pay for, and the exact nature of the materials 

 accomplishing the results is in reality of secondary importance; 

 but when coal-tar colors are to be used in foods, and in addition to 

 tinctorial effect the absence of any physiological action is necessary, 

 it is at least of doubtful propriety to market such corrected or adjusted 

 brands unless the correction or the adjustment be made with harmless 

 colors. 



There are a few instances in the relevant literature where it was 

 attempted to explain the different results attained by observers by 

 the difference in the composition of the materials subjected to physio- 

 logical test, and there are other instances showing the difficulties 

 encountered in obtaining specimens of coal-tar colors which would 

 always give favorable physiological result. 



The variation in composition of coal-tar colors may be exemplified 

 by the following excerpts from the literature: 



1. Weyl (p. 91), discussing the differences between his results and 

 those of Cazeneuve and Lupine with Naphthol Yellow S, states as 

 follows : 



It is to be noticed, however, that Cazeneuve and Lupine state that the Naphthol 

 Yellow used (Jaune NS) was difficultly soluble, eo that they probably experimented 



