This synopsis, together with the classification of colors and the 

 methods of analysis which follow, is intended as an outline for the 

 examination of food stuffs for colors, to be elaborated during the 

 progress of the work. 



CLASSIFICATION OF COLORS. 



As a guide to the food analyst, a compilation is given of the vege- 

 table and animal colors, lakes and pigments, which he may be called 

 upon to examine either as to composition and origin or as to suitabil- 

 ity for food colors. Many of the old vegetable colors have, of course, 

 been discarded for the coal-tar d}^es now employed, which are also 



classified. 



I. Coal-Tar Color Lakes. 



1. The principal materials used in the preparation of lakes from acid dyes are: 



Barium chlorid. 

 Lead nitrate and acetate. 

 Zinc sulphate. 



Aluminum sulphate and acetate and potash, sodium and ammonium alums. 

 Tin chlorid. 



Antimony chlorid, tartar emetic, double flourids of antimony and sodium or 



potassium. 

 Calcium nitrate and acetate. 



2. Those from basic dyes are: 



Tannic acid. 



Phosphate of soda. 



Sodium arsenite. 



Stannic and stannous acids and salts. 



Antimony acids. 



Resinic and various fatty acids. * 



3. Principal bases used to modify the color and physical properties of lakes are: 



Barium sulphate (barytes, blanc fixe, heavy spar). 



China clay (kaolin). 



Calcium sulphate (Paris white, satin white, gypsum). 



Kieselguhr (infusorial earth). 



Red lead. 



Zinc oxid. 



Lead sulphate. 



Aluminum hydrate. 



Aluminum arsenite. 



Barium phosphate. 



Lead carbonate. 



Calcium phosphate. 



Lampblack and vegetable black. 



Green earth. 



4. Colors used may be classed under: 



(1) Acid triphenylmethane colors. 



(2) Basic tryphenylmethane colors. 



(3) Azo colors. 



(4) Oxyketone colors. 



(5) Azin colors. 



a Jeimison, Manufacture of Lake Pigments, 1900. 



