50 



BULLETIN 448, U. S. DEPARTMENT OF AGRICULTURE. 



brownish. With most of the others it is ill-defined and is probably 

 often produced by a small fraction of the dye that has escaped 

 destruction by bromin. In acid solution these dyes are merely 

 destroyed by bromin m most cases, the results being as given for E. 



Class E. — Dyes in this class are similar to those in Class D, but 

 show no color changes other than bleaching, on addition of bromin. 



Class F. — Halogenated jiuorescein derivatives and similar com- 

 pounds. — These dyes are very resistant to bromin. The nonfluo- 

 rescent iodin compounds tend to become yellower in shade and to 

 develop a green fluorescence, probably due to partial substitution of 

 iodin by bromin. 



Table 4. — The bromin test: Classification of colors according to reactions obtained. 



[NumlDers denoting permitted dyes are in boldfaced t3rpe; natural colors are in italics. Dyes common in 

 foods are starred, three stars indicating those most often found. Statements apply in. general to 0.01 per 

 cent solutions.] 





Color- 







Color- 







Color- 







Color- 





No. 



ing 

 matter. 



Class. 



No. 



ing 

 matter. 



Class. 



No. 



ing 

 matter. 



Class. 



No. 



ing 

 matter. 



Class. 



1 



*462 



D or E. 



33 



56 



A (e). 



65 



*92 



A(w). 



87 



*468 



E. 



2 



434 



D. i 



34 



*62 



AA.(e). 



66 



101 



A or AA 



88 



464 



E. 



3 



435 



D. '■ 



35 



*=i=64 



AA(e). 







(w). 



89 



438 



D. 



4 



*436 



D. ; 



36 



*85 



AA(e). 



67 



102 



A (w). 



90 



**433 



D. 



5 



439 



E. 



37 



**103 



A or AA 



68 



483 



E. 



91 



442 



E. 



6 



491 



D or E. 







(w). 



69 



*510 



(5) 



92 



476 



E. 



7 



440 



E. 



38 



139 



A or AA 



70 



26 



A (e). 



93 



240 



A. 5 



8 



**602 



E(B).i 







(w). 



71 



220 



A.i 



94 



277 



A. 



9 



**108 



A (w). 

 A (w). 



39 



164 



A (w). 



72 



269 



A.i 



95 



562 



B. 



10 



***8 



40 



**667 



B. 



73 



512 



E.- 



96 



658 



E. 



11 



9 



A (w). 



41 



*169 



A (w). 



74 



515 



E. 



97 



496 



D orC. 



12 



**89 



A (w). 



42 



163 



A (w). 



75 



516 



E. 



98 



650 



EorC. 



13 



692 



E. 



43 



170 



A(w). 



76 



517 



E. 



99 



639 



EorD. 



14 



399 



A (w). 



44 



84 



A (w). 



77 



518 



E. 



100 



*5S4 



B orC. 



15 



***106 



A (w). 



45 



146 



A(e). 



78 



520 



E. 



101 



**448 



E orD. 



16 



107 



AA or A ! 



46 



287 



A.i 



79 



521 



E. 



102 



***425 



E orC. 







(w). i 



47 



78 



A. 2 



80 



*523 



E. 



103 



426 



E orC. 



17 



94 



A (W). ; 



48 



***7i0 



E. 



81 



2 



E. 



104 



***451 



E or C. 



18 



*398 



E- 



49 



*546 



B.i 



82 



*3 



E. 



105 



452 



E orC. 



19 



605 



B. ! 



50 



1 



E. 



83 



6 



E. 



106 



**427 



D orC. 



20 



604 



B. 



51 



507 



D. 



84 



5H 



B. 



107 



428 



D orC. 



21 



188 



AA (w). 



52 



328 



A (w). 



85 



*^707 



E. 



108 



*197 



A or C. 



22 



***14 



A (e). 



53 



■ 606 



B. 



86 



*10 



A (e).4 



109 



*201 



A or C. 



23 



21 



A (e). i 



54 



154 



A (e). 









110 



17 



AorC(e). 

 A or C (e). 



24 



318 



A.i 



55 



85 



A (w). 









111 



18 



25 



20 



A (e). \ 



56 



**13 



A (e). 









112 



505 



D ore. 



26 



93 



A or AA 1 



57 



***86 



A (w). • 









113 



499 



D orC. 







(w). i 



58 



97 



A (w). 









114 



***504 



D orC. 



27 



"***480 



D. 



59 



54 



A(e). 









115 



502 



D orC. 



28 



*53 



A (e). 1 



60 



329 



E. 









(0 







29 



*55 



A (e). 



61 



139 



A (w). 















30 



105 



A (w). 



62 



157 



A (e). 















31 



4 



E. i 



63 



*95 



A(w). 















32 



*=i=i-706 



E. ; 



64 



88 



A (w). 















1 Imperfectly. 



2 Some alcohol should be added before the alpha-naphthol. 



3 Gives eosin. 



< Of the oil-soluble dyes given in the other tables all belong to type A except Quinophthalon, which ia 

 60 per cent acetic acid shows reaction indicated under B. 

 = Very imperfectly. 



REACTIONS WITH NITROUS ACID. 



By treatment with nitrous acid in dilute solution most of the com- 

 mon coal-tar dyes used in food coloring are not readily affected. A 

 considerable number, however, show marked changes, because of di- 

 azotization of free amino groups, of formation of nitroso compounds, 

 or of direct oxidation. 



