<a eS 
PERMITTED COAL-TAR FOOD DYES 13. 
the blue color, however. On adding sodium hydroxide the aqueous 
solution turns green to yellowish green. Indigotine is sparingly sol- 
uble in alcohol. With concentrated sulphuric acid it forms a bluish- 
violet solution, which turns blue when diluted with water. The 
color of the aqueous solution of this dye is fugitive to light. 
In 1890 the following patents for the preparation of indigotine 
were issued: German patent 63,218 (9); British patent 8,726 (7); 
French patent 206,567 (7). In 1893 German patent 68,372 (7) was 
issued. In 1894 United States patent 524,256 (7) was issued. 
The percentages of impurities tolerated in this dye, the analytical 
data needed in foundation and supplemental affidavits (70), and the 
methods for determining these data are shown in Table 11. 
TABLE 11.—Specifications for indigotine 
epee M Method of 
olerance inimum ethod o 
Component (ratio to pure| tolerance analysis 
coal-tar dye) | 
Per cent Per cent Page 
1 TS ATEREL 2 Rt Ae pee a Se a ea nee LZ. ORS (Se eee oS 14, 
Insoluble matter: 
OIL. ue oe ST eee Sei ee See ee 15, 
isTanan Rb ee ene as ke ee IE as Bins rage ee, ee 15. 
LE Geo ess CR ES See ek Se nee ee eee DsO ho | ees a Pes 15, 16 
ee ees re Bis beter i 
Ree see ae ee oe Ee Ee ro eS OY oh eet eee 
peat GbE’ ITIRCOLOKS Bet a8 a8 oe oe ec, tah ee ieee Pheoretical.. (2352222. 3 18. 
eeeMSUMLTI Cpl Seo sy me os SS le SE 8 Sv ae NS INone: tS. = 19. 
Ta EESTI 5 0 Sai hs th ce Be 9 es BRR ree eee ee SC ected (gee ee 19. 
|. 8 FUG, Gee a ee ee Se een ee ee Sic) lees dee: 19 
a ae ln ee a ae ee ae ee 1 rams ted al Need oe a mt 19 
VD. ele cee SS Se eae ee ees Eee ea ones eee BESO iss eee 19. 
(a BESS sD Se ae ee ee SO0QTE |7  ae  S 22, 23. 
Ether extractives: 
1 ene? Se ee SO RY a ee ee ee ie Qle-y aryl = Se 23. 
LNUGN ES Sa he pa ST es eek ome eee ee (OS 77 i |pee= ste GY 
BD eS OS By aoe Be ee eee bee es (OSES AE ete 24, 
(DUE oe - Joa i ee eee eee Aes ae Se ei 24, 
reas EMIT SITICON On ste = ee Ee rns Pe 2 ee eo se *Bheéoreticals-fo- 2 t=? 24, 
(. TAT SOG Se te) eee oS a a eee ee ee eee | oes oe ated 74. 3 | 25. 
(PE GOBLET. ORD RS ua a Et A WR 82.0 | 26 
Maron sim pnonaped @yes_-3 99+. 2224s 82 eee ed | DOR, sees eee 29. 
1 Although no limit is here defined, a statement of the percentage found by analysis must be incorpo- 
rated in the foundation and supplemental affidavits (70). e 
METHODS OF ANALYSIS OF PERMITTED COAL-TAR FOOD DYES 
The methods of analysis of coal-tar dyes intended for use in 
coloring foods are subject to revision as the result of the development 
of more refined or simpler procedures. The methods here described 
are the ones now used in the Bureau of Chemistry (13, 43, 45, 46, 47, 
48, 49, 50, 51, 52, 58, 54, 55, 63). Acknowledgment is made and 
thanks are extended to the manufacturers and their staffs for sug- 
gestions and criticisms in this work. 
REAGENTS 
In these methods the term “concentrated sulphuric acid’’ denotes 
an acid having a specific gravity of 1.84; “strong hydrochloric 
acid,’ an acid having a specific gravity of 1.184; “strong nitric 
acid,’ an acid having a specific gravity of 1.42; and “strong ammo- 
nium hydroxide,” a base having a specific gravity of 0.90. In the 
