O F 
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UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT BULLETIN No. 1390 
SUPPLEMENT No. 1 
Washington, D. C. T Issued March, 1930 
CHEMISTRY AND ANALYSIS OF THE PERMITTED COAL-TAR FOOD 
DYES PONCEAU SX, SUNSET YELLOW FCF, AND BRILLIANT BLUE 
FCF 
By O. L. Evexsox, Associate Chemist, and H. T. Herrick, Principal Chemist 
in Charge, Color Certification Laboratory, Food, Drug, and Insecticide Admin- 
istration 
INTRODUCTION 
Since the revision, in December, 1927, of Department Bulletin 
1390 (2) 1 three new colors — ponceau SX, sunset yellow FCF, and 
brilliant blue FCF — have been approved and added to the list of 
permitted coal-tar food colors. The chemistry and special analytical 
methods for these three new dyes, as well as a revised method for lead, 
follow. 
CHEMISTRY OF THREE NEW PERMITTED COLORS 
PONCEAU SX 
Ponceau SX, a monazo dye (C 18 H 14 N207S2Na2), is the disodium 
salt of the product obtained by coupling diazotized l-amino-2-4- 
dimethylbenzene-5-sulphonic acid with l-naphthol-4-sulphonic acid. 
These intermediates are used singly in other dyes listed in the Colour 
Index (11). The first component is the monosulphonic acid ob- 
tained by sulphonating asymetric w-xylidine, l-amino-2-4-dimethyl- 
benzene. with 20 per cent oleum at temperatures in the neighborhood 
of 100° C. (Witt, G. P. 34,854, 1885 (14).) The m-xylidine is usually 
separated from crude xylidine as the acetate (G. P. 39,947, 1886 
(10)). Nevile and Winther's acid, a-naphthol-4-sulphonic acid, the 
second component, is easilv obtained of a satisfactory degree of purity 
(G. P. 46,307 (1) and G. P. 109,102 (3)). 
Ponceau SX, when ground, is a red powder, easily soluble in water 
and dilute alcohol and slightly soluble in 95 per cent alcohol. The 
neutral aqueous solution is red, turning to a bluish red in high dilution. 
Addition of alkali changes the color to orange, and addition of acid 
causes a slightly more reddish tint. The dye dissolves in concen- 
trated sulphuric acid, forming a bright cherry -red solution. When 
this solution is poured into water the dye partly precipitates and then 
redissolves. 
; Italic numbers in parentheses refer to "Literature cited," p. 7. 
86180—30 
