2 BULLETIN 1390, U. S. DEPARTMENT OF AGRICULTURE 
-and in scientific publications (45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55) ; 
others have been announced only through official correspondence. 
The present procedure for certification is outlined in United States 
Department of Agriculture Miscellaneous Circular 52; the chemis- 
try of the permitted coal-tar food colors and the revised methods of 
their analysis are fully described in the following pages. 
CHEMISTRY OF THE PERMITTED COAL-TAR FOOD DYES 
In the preparation and purification of dyes to be certified care 
must be taken not only in the final steps of their manufacture, but 
also in the synthesis or purification of their intermediates. Many | 
intermediates are commercial products containing relatively large 
proportions of isomeric and subsidiary compounds, which will pro- 
duce isomeric and subsidiary colors durmg the preparation of the 
dye. Some of these impurities are harmful, and all are undesirable 
adulterants. Purification of adulterated intermediates is not worth 
trying. The only safe method is to use intermediates of the best 
possible quality. The Bureau of Chemistry has refused to approve 
for certification several batches of dyes because they contained 
foreign coloring matter. These rejections would not have been 
ade if intermediates of suitable quality had been used. 
Several of the permitted dyes can be prepared by more than one 
method. The method of manufacture is immaterial, so long as the 
final product meets the proper specifications. The incorporation 
in the foundation affidavit (70) of an outline of the method of manu- 
facture, with the names of the intermediates used and the process 
employed, gives helpful information to the analysts who seek to 
verily the identity of the dye. If the firm submitting the founda- 
tion affidavit does not manufacture but simply purifies commercial 
dyes, an outline of the process of purification is of material aid in 
the examination of the dye. Such information is not required, but 
it is very helpful. When incorporated in the foundation affidavit 
it is held in strictest confidence by the Bureau of Chemistry. 
With the exception of yellow A B and yellow O B, the permitted 
coal-tar dyes are hygroscopic. Consequently, when a dye is being 
repared with a view to requesting its certification, after the batch 
Be been finely ground and mixed to uniform composition, it should 
be dried only to the condition m which it would neither lose nor 
gain unduly large quantities of moisture if exposed for brief periods 
to an atmosphere of normal humidity at the place of preparation. 
PONCEAU 3R 
Ponceau 3R (Cy>HigN20;5,Na,), amonazo dye(68), is made by diazo- 
tizing crude ¥-cumidine and’coupling the product with ‘“‘R” acid (@- 
naphthol-3-6-disulphonic acid). Because crude y-cumidine is a 
mixture, it is necessary to define the grade which may be used in 
the manufacture of the dye. The product from pure ~-cumidine, 
known as ponceau 4R, has such a strong bluish-red color that it has 
proved unsatisfactory. The shade wanted is produced from crude 
y-cumidine having a boiling point of 220° C. or higher. The affi- 
davit (70) accompanying a sample of ponceau 3R to be certified 
must contain a statement of the boiling point found by testing the 
crude ¥y-cumidine used for the batch concerned. 
