SCOPE OF THE INVESTIGATION. 



The field of color chemistry is very large, and the chemist in gen- 

 eral analytical practice often neglects it owing to the vast amount of 

 time and patience required for an intelligent understanding of the 

 subject. Much good work has been done toward establishing methods 

 for the recognition of coloring matters in food stuffs, but with the 

 data at present available for such work the individual operator will 

 find himself called upon to exercise his own judgment and apply his 

 own experience to the subject-matter in hand. 



The introduction of coal-tar dyes into the field of food stuffs com- 

 plicates enormously the scope of the work to be covered in an exami- 

 nation of artificial coloring. Were it possible to limit the examination 

 to a certain number of colors, the work would be materially simplified, 

 but no sooner has the analyst perfected color schemes and tabulated 

 reactions for the identification of such colors when new ones are found, 

 rendering previous schemes to a certain extent unreliable and neces- 

 sarily subject to alteration. 



Hence the most tnat can be hoped for is to establish general methods 

 for determining whether artificial coloring has been resorted to, and, 

 if so, whether the coloring matter is of mineral, vegetable, or coal- 

 tar origin. This fact having been established, special methods must 

 be applied for the separation and identification of the individual color- 

 ing matters, often complicated by the presence of mixtures of several 

 coal-tar colors, rendering color reactions useless until each of the sep- 

 arate colors has been isolated. 



The food chemist may be called upon for an examination of the 

 coloring matters and commercial preparations used for coloring foods, 

 and for the examination of foods for' the presence of artificial color- 

 ings, identification of the added color, and the presence of poisonous 

 metals due to the latter. He may also be called upon for an opinion 

 as to the toxic or nontoxic character of the coloring matter, which 

 not only requires an examination for poisonous metals present, as lakes 

 and pigments, but in addition the determination of the presence of 

 poisonous metals due to impurities, the identification of the color or 

 colors, and a knowledge of the toxic effects of the pure color per se. 



An examination, therefore, of the colors and preparations employed 

 involves the identification of the heavy metals present, the nature of 

 the color entering into the lake, whether vegetable or of coal-tar 



(3) 



