UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 448 
Contribution from the Bureau of Chemistry 
CARL L. ALSBERG, Chief 
Washington, D. C. 
PROFESSIONAL PAPER 
February 15, 1917 
SEPARATION AND IDENTIFICATION OF FOOD 
COLORING SUBSTANCES. 
By W. E. Mathewson, Assistant Chemist. 
CONTENTS. 
Introduction 1 
General statements concerning reagents used 
in color analysis 2 
Preliminary treatment of food products 4 
Page. 
Separation and purification of coloring sub- 
stances S 
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 
all those coal-tar colors (except a few entirely obsolete nitro dyes) 
which have been mentioned in the literature 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 account all possible colors and combinations of colors; never- 
theless 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 little used in food products. 
The scheme of separation described is designed to meet actual con- 
ditions, one of which is the relatively more frequent occurrence of 
the eight colors the use of which in food is permitted by the United 
States Department of Agriculture 1 — Amaranth, Ponceau 3 R, Ery- 
1 Food inspection decisions Nos. 76 and 184. 
Note.— This bulletin will be of interest chiefly to chemists engaged in food analysis. 
61147°— Bull 448—17 1 
