52 BULLETIN 448, TJ. S. DEPAETMENT OF AGBICULTUEE. 



21. — With sodium nitrite, slightly darker; with alpha -naphthol and sodium carbon- 

 ate, dull greenish black. 



318. — With sodium nitrite, paler and redder. 



20°, 93° (480°.— Slowly attacked by nitrous acid); 53°, 55°, 105°, 4°, 706°, 56°, 62°, 

 64°, 65°, 103°, 139°, 164°, 667°, 169°, 163°, 170°. 



84. — With sodium nitrite, redder. 



146°, 287°, 78°, 710°, 546°, 1°. 



507. — With sodium nitrite, bluer. 



328°, 606°, 154°. 



85. — Vfith sodium nitiite, paler. 



86°, 54°, 13°, 97°, 329°, 139°, 157°. 



95. — Ciimson solution becomes yellow with sodium nitrite; on addition of hydrazin 

 sulphate, red again. 



88. — Crimson solution becomes yellow with sodiiim nitrite; on addition of hydrazin 

 sulphate, red again. 



92°. 



101. — Paler with sodium nitrite. 



102°, 483°, 510°, 26°. 



220, 229. — Slightly paler with sodium nitrite. 



512°, 515°, 516°, 517°, 518°, 520°, 521°, 523°, 2°, 3°, 6°, 534°, 707°, 10°, 468°, 464°, 

 438°, 433°, 442°, 476°, 240°, 277° (562°, scarcely attacked; in 50 per cent acetic acid, 

 behaves with nitrous acid as with bromin inthebromin test); 658°, 496°, 650°, 639°. 



584. — With sodium nitrite, blue; rather rapidly becomes red again on addition of 

 hydrazin sulphate. 



448. — ^Wine-red on diazotization, addition of hydrazin sulphate, alpha-naphthol 

 and sodium carbonate; with sodium nitrite in acetic acid solution, first blue, then 

 colorless. 



425°, 426°, 451°, 452°. 



427. — Reddish with sodium nitrite. 



197°, 201°. 



17. — ^With sodium nitiite, paler; after addition of sodium carbonate, naphthol, etc., 

 somewhat redder. 



18. — With sodium nitrite, paler; after addition of sodium carbonate, naphthol, etc., 

 somewhat redder. 



505°, 499°, 504°, 502°. — May appear bluer when the alcohohc alpha-naphthol 

 solution is added. 



16°. — Slowly destroyed by nitrous acid. 



7. — Paler with sodium nitrite; after addition of other reagents, red. 



Aminoazotoluene. — As stated above for 7. 



Benzeneazo-)3-naphthylamin, Ortho-tolueneazo-/3-naphthylamin. — These com- 

 pounds are almost insoluble in aqueous liquids. As ortho-aminoazo derivatives, they 

 are not readily diazotized or coupled. 



REACTIONS WITH POTASSIUM CYANID. 



With tlie common m^onazo dyes, the bromin oxidation will pro- 

 vide for an identification of the "first component" of the color, i. e., 

 the radical not containing the hydroxyl or amino groups. The other 

 radical, usually containing hydroxyl or amino groups ortho to the 

 azo junction, is identified with much more difficulty in most cases. 

 Since the two ortho-azo dyes permitted in foods are both derived 

 from 2-naphthol-3-6-disulphonic acid as second component, the reac- 

 tion discovered by Lange ^ that derivatives of this acid are attacked 

 on boihng with potassium cyanid and the 3-sulphonic acid group 

 replaced by cyanogen, is useful for distinguishing and separating 

 isomeric dyes. 



The test may be made as follows: About 10 cc of the neutral color 

 solution is treated with 1 cc of 20 per cent potassium cyanid solution 



1 Deutsches Reichs Patent No. 189,035. 



