FOOD-COLOEING SUBSTANCES. 49 



reactions take place, so that a more or less strong coloration is pro- 

 duced on treatment with sodium carbonate without previous addi- 

 tion of the naphthol. Crystal Scarlet (No. 64), Bordeaux B (No. 65), 

 and Palatine Red (No. 62) give strong blue colorations; Naphthol 

 Black (No. 88) and Amaranth (No. 107) a less intense blue color. 

 Azorubin (No. 103) gives a piu'ple changing to bluish red, but not 

 very intense. Except for the fii'st three dyes named, the colora- 

 tions are considerably less intense than the original dyes, and the 

 reaction much less trustworthy and valuable than the smooth, 

 almost quantitative, reaction in acid solutions. When treated with 

 bromin in solutions containing sodium carbonate (one-fourth nor- 

 mal), Nos. 62, 64, and 65 are bleached, becoming intensely blue on 

 addition of hydrazin sulphate. 



Class B. — Azin derivatives,^ etc. — On treatment with bromin in 

 neutral or acid solutions, the color is readily bleached, but is restored 

 on adding hydrazin sulphate. Sodium carbonate and alpha- 

 naphthol plus sodium carbonate produce no change other than that 

 shown by the origmal dye solution on treatment with alkali. A few 

 dyes of Classes A and AA when oxidized in neutral solutions tend to 

 show a rather marked coloration on adding the hydrazin sulphate. 

 However, with the typical members of Class B, the dye maybe bleached 

 and restored a number of times by careful alternate addition of the two 

 reagents, the bromin apparently f ormmg a nearly colorless compound 

 reconverted into the original dye on addition of the hydrazin sulphate. 



Class C. — Colors giving precipitates at dilutions as high as 0.01 per 

 cent. — This class includes most of the basic dyes. 



Class D. — Colors showing marlced changes in tint in neutral or very 

 faintly acid solution on addition of hromin.^ — The colorations are 

 usually produced by a mere trace of the halogen and destroyed by 

 excess, and the reactions are consequently not very dependable or 

 valuable. With many of the dyes of this type containing alkylated 

 amino groups the color change would seem to be due to elimination 

 of alkyl radicals. In general with dyes of this group the coloring 

 matter, while readily altered, is completely l)roken down by bromin 

 only with difficulty. On addition of hydrazin sulphate no change 

 takes place other than that due to removal of the excess of the col- 

 ored halogen.^ The coloration with alpha-naphthol and sodium 

 carbonate is identical with that produced by sodium carbonate 

 alone. With most of the yellow coloring matters of this group it is 



I Quinofjiilhfilon ))y troalmont with bromin Hrst fonn.s llu; unstable colorless iiddilion product con- 

 taining two alom.s of bromin in the molwulo (lOibnur and F/anKo, Llobig's Annalon dcr (^licmie, '.ilS 

 (1901;, 'M'l). For action on azin dyes wmpare Vaubel, .!. prakt. Cliem., Hi (iKWi), 2H!). 



' According to Houmann, Die Anilinfarben, vol. 1, p. 11, Malacjiilo (Ireen sohil.ioii, on oxidation with 

 lead p*'roxld and af«l ic svid, becomes violet, and then contains the salt ot dlumiuotripheuylcarbinol. 

 Compare lurlhcr Vaulxd, J. prukt. fJhem., flO (1H94), 347. 



' Cblorin wator may be ascd if preferred. 



