FOOD-COLORING SUBSTANCES. 



53 



and 1 cc of 20 per cent ammonium chlorid solution^ and is heated in 

 a test tube in a boiling water bath for from five to eight minutes. It 

 is then quickly cooled. The reactions obtained with certain dyes are 

 sho%vn in the table. The test requkes some care, and blanks with 

 known dyes should be carried through at the same tim.e in aU cases. 



The results Tsnith a number of common azo dyes are shown in 

 Table 6, the derivatives of 2-naphthol-3-6-disuiphonic acid forming 

 new dyes of markedly different solubihties, corresponding to the fact 

 that they contain one less sulphonic acid group. By warming with 

 the cyanid solution for a considerable period of time further reac- 

 tions easily take place, derivatives of 2-naphthol-3-6-disulphonic 

 acid and 2-naphthol-6-8-disulphonic acid being especially unstable. 



The common nitro dyes are changed by warming with cyanid 

 solution, becoming brownish or reddish (compare formation of iso- 

 purpuric acid from trinitrophenol) . 



Table 6. — Behavior of colors with cyanid solution. 



Dye. 



"Second component" o 



f dye. 



Behavior with cyanid solution. 



108 



Naphthol 



trisulphonic 



acid 



Warmed 8 minutes, dye almost completely destroyed with 





(2-3-6-S). 





production of orange and yellow substances. Warmed 











until darkred (1-2 minutes), strongly acidified, and waslied 











with 2 N HCl, practically no color is removed (3-4 wash- 











ings) ; then washed with N/4 HCl, a bluishred dye is readily 











removed. 



Azorubin 

 S G 









Apparently imchanged by cyanid. 



' 106 



Naphthol 



(2-6-8). 



disiilphonic 



acid 



Dyo is not clianged in solubility, although on long warming 

 much color is destroyed. The cyanid mixtiue may be 

 acidified with 5 cc concentrated hydrochloric acid, and 

 slialien out with 10 cc of amyl alcohol. On separating the 

 alcoiiol, and washmg 4 or 5 times witli fourtli-normal hydro- 

 chloric acid, nearly all of the dye will be taljen out by the 

 dilute acid. 



Dye is changed into a cyan-derivative sunilar in solubility to 



107 



Naphthol 



disulphonic 



acid 





(2-3-6). 







other disulphonated monazo dyes. The cyanid mixttue 

 is pale brown and when treated as stated under New 

 Coecin (106), almost all coloring matter remains in the 

 amyl alcohol. On long heating of the cyanid mixture the 



















cyan-derivative may be completely destroyed, further re- 











actions taking place. 



14 



Naphthol 



(2-^s^ 



disulphonic 



acid 



Dj'e unchanged. Cyanid mixture, when acidified wiih 1 cc 

 glacial acet ic acid and shaken with 5 to 10 cc amyl alcohol, 

 gives up little colormg matter to (he latter. 



15 



Naphthol 

 (2-3-6;. 



disulphonic 



acid 



Dye changed into a cyan-derivative similar in solubility to 

 the other monosulphonated monazo dyes. The cyanid 

 niixluro is pale t)ro\vni.sh, an-d when treated as descriliod 

 under Orange (14) gives up most of its coloring matter 

 to the alcohol. 



20 



DIoxynaplithal 



en e 



As slated for 14. 





flisiilphonic aci<l (1-s- 



3-«). 





21 



Aminonap 



hthol disulphonic 



.\.s stated for 14. 





acifl n-h 



-3-<i). 







52 



Naphthol 

 (1-J-S). 



.Nar-hthol 

 (i-.',-ti). 



-Saplithol 



disulphonic 



acid 



.Vs stated for 14. 



53 



disulphonic 



acid 



.\s stated for 14. 



55 



disulphonic 



acid 



As statefl for 15. 





(2-3-<i>. 









56 



Naphthol 

 (2-3-^1). 



disulphonic 



acid 



As stated for 15. 



62 



Naphthol 

 (l-3-<i). 



disulphonic 



acid 



As stated for 14. 



64 



Naphthol 



(2-<l-S;. 



Naphthol 



disulphonic 



acid 



AsstatGfl for 14. 



65 



disulphonic 



add 



A.S8tate<I for 15. 





(i!-3-«). 









