UNITED STATES DEPARTMENT OF AGRICULTURE 



Contribution from the Bureau of Chemistry 

 CARL L. ALSBERG, Chief 



J^.^"^W(L 



Washington, D. C. 



PROFESSIONAL PAPER 



February 15, 1917 



SEPARATION AND IDENTIFICATION OF FOOD- 

 COLORING SUBSTANCES. 



By W. E. Mathewson, Assistant Chemist. 



CONTENTS. 



Page 



Introduction 1 



General statements concerning reagents used 



in color analysis 2 



Preliminarj' treatment of food products 4 



Page. 



Separation and purification of coloring sub- 

 stances 8 



Identification of coloring substances 35 



INTRODUCTION. 



The scheme of analysis of dyes described in this bulletin embrace 

 about 130 chemical individuals. This number comprises practically 

 ail those coal-tar colors (except a few entirely obsolete nitro dyes) 

 which have been mentioned in the hterature as having been found 

 in food products, and those mentioned as being suitable for the 

 coloring of foods. A number of dyes which are typical represen- 

 tatives of certain classes and which exemplify in a general way the 

 analytical properties of certain groups, also have been included. No 

 process for the analysis of dyes can be made so complete as to take 

 into accoiuit all possible colors and combinations of colors; never- 

 thrless the analyst should be prepared for as many as possible of 

 the cases arising. It is especially difficult to take the newer colors 

 into consideration, but, fortunately, at the present time these are 

 very littl(! used in food products. 



The scheme- of separation d(!scribed is designed to meet actual con- 

 ditions, one of which is the relatively more frequent occurrence of 

 the eight colors the use of whicli in food is ])ermitt(Hl by the United 

 States Department of Agricultuni' Amaranth, Pom^eau 3 K, Ery- 



• Food laspoctlon decisions Nos. 70 and IM. 



NoTB.— This bulletin will bo of interest chiefly to chemists engaged in food analysis. 

 f.lM7*-Uiill 44S~J7 1 



