origin, its identification, and, in the case of mixed colors, their separa- 

 tion and identification, and, lastly, the presence of poisonous metals as 

 impurities in the coal-tar dyes, or their presence as inherent constit- 

 uents of the colors themselves. 



Many of the colors contain metallic constituents, as in the triphe- 

 nylmethane derivatives, especially the greens, such as malachite green, 

 iodin green, ethyl green, victoria green, etc., which contain a double 

 chlorid of zinc in combination with the organic matter. Some of the 

 acridines and thiazines also contain zinc, and naphthol green B contains 

 iron. 



In the preparation of the coal-tar dyes many become contaminated 

 with arsenic, copper, zinc, tin, lead, etc. , from the use of these metals 

 and their salts during the process of manufacture. Sulphuric acid 

 being used in some stage of the process of manufacture of nearly all 

 the dyes introduces the danger of arsenic being present. Hence all 

 dyes used for artificial coloring which in themselves are harmless 

 may become injurious from the presence of these poisonous ingredients, 

 unless highly purified. 



While alum lakes of the vegetable colors are in general harmless, 

 the presence of lakes of tin, antimony, etc., should be carefully 

 guarded against. 



The vegetable colors should be examined for the presence of coal- 

 tar dyes of a dangerous nature, and for other vegetable colors and 

 substances and inert mineral matter added for cheapening. 



The examination of the food stuffs themselves necessitates deter- 

 mining whether the coloring is due to natural or artificial means, and, 

 if' the latter, the color or colors must be separated and an examination 

 of the material made for heavy metals. 



In regard to the toxic effects of the purified coal-tar dyes, the chem- 

 ist must rely upon the experiments and conclusions of investigators in 

 this line of work, and should hesitate to express an opinion on a new 

 color without a physiological test upon living organisms. The experi- 

 ments of Konig, Weyl, and others should be consulted on this subject. 



Frenzel 6 found that mandarin (sulphanilic acid azo-B-naphthol) and 

 metanil yellow (m. benzene sulpho acid, azo-diphenylamin) could 

 scarcely be considered poisonous in the small quantities in which they 

 are used in foods, but long-continued, large doses give rise to some 

 injurious effects. 



Hygiene of Coal-tar Colors, Koster, Heidelberg, 1882; Poisonous Metals in Dyes, 

 Ashwell and Forth, J. Soc. Chem. Ind., 5, 226, 301; Theerfarben mit besonderer 

 Riicksicht auf Schadlichkeit u. s. w., Dr. Thos. Wehl, 1889; The Sanitary Relations 

 of the Coal-tar Colors, by T. Wehl, Philadelphia, 1892; Effects of Coal-tar Colors on 

 Digestion, Arner. Chem. J., 8, 1092; Conn. Agr. Expr. Stat. Kept, Winton, 1901, 

 p. 179. 



&Zts. Nahr. Geimssm., 1901, 968-974. 



