39 



Since i he promulgation of F. I. D. 7G of the Board of Food and Drug Inspection, 

 allowing the u-e ..f . rtain coal-tar colors in food products and prohibiting all others, 

 it ha.< become quite necessary for food chemists to make a study of the methods of 

 identifying color- \<> find out with what degree of accuracy these methods serve their 

 purpose. In making this study it is of course very essential to work with pure colors, 

 and a.- the time available for this work would not allow of preparing these colors in 

 the laboratory, there were used colors furnished by manufacturers, who in most cases 

 gave both the commercial and the scientific name of these samples, and upon them 

 such tests were made as seemed necessary to establish fully the fact that they corre- 

 sponded \\-ith the names givMi and were' simple unmixed colors. 



\o originality in the methods of testing is claimed, the standard works of reference 

 on the subject having been freely consulted. In every case the well-known tests by 

 color reactions in aqueous solution, on the dyed fiber, and with concentrated sulphuric 

 acid on the dry color were u.-ed. This includes a test for mixed colors made by 

 sprinkling dry color on a surface wet with water or concentrated sulphuric acid. In 

 addition the following tests were made on the separate colors: 



I'ri-fifiitaiinn by alcohol: Concentrated aqueous solution + 95 per cent alcohol= 



Iline yellow precipitate. 



o.i i r f nt <i<{ii' <>n -\-stannou8 c/ZorW= yellow precipitate, soluble in 



oxalic acid .-olutiou (10 per cent . 



O.I pt-r cent aqueous solution + harimn chl<>ri<l .so/<//MM=yellow precipitate. 

 a. i JMT cent aqueous solut < >n chlnrid solution - ; no precipitate. 



3, c<c .1. !M. 



ICON: 



for coal-tar color- ; n :ni nation. 



1 ;re c..l,,r. 



NAPHTHOJ 



r reaction with -Minions chlorid and ammonia. Test for organic sulphur. 

 >//////// ' I on platinum foil. Takes fire explosively. 



lv iiiMilublc in neutral or acid solution. 



i- barium chlorid solution (10 per mi<)=orange precipi- 

 Insoluble 



" ./ jr cent aqueous solution^- calcium cktorid solution (to j><r rr/t/)=no precipitate. 



n.i mimon* solution + It-ad r<7<i/<' = onini:r pre<-ipitate, soluble in acetic acid. 

 '/./ /neon* sola ' '/ </ lonil 11 ml caustic soda= olive-green precipitate. 



ll.iourl:*: (\r nearly pure. Contains small amount of unsulphonated naphthol 

 yellow. 



TKMI-U .)UN O O: 



Kediirtion of c..lor by stannous chlorid in acid solution; separation of para amino- 

 diphenylamin fr-m alkalin.- - -lution by ether. Melting point, 61 to 62 C. 



/'/ hij salt: 0.1 j>er cent solution of color -f few drops 10 per cent sodium 



chlorid -olmion -precipitate ..f color. 



0.1 i>tr 'on + barium chlorid (10 per eett<)= colored precipitate, 



like F- "11 



0.1 per cent aqueous solution + calcium chlorid (10 j>crcent)=co\ored precipitate, like 



'!! 



Com ' ire color, S. & J. 88. 



KKYTHKOSIX: (Color used in sample :J ('.) 



Aq ueous s. >lu t ion , | )ink tlm )rescent (shows presence of other colors besides erythrosin.) 

 <'olor .-xtracte.l ir,, m acidified aqueous solution by ether. Ether solution washed 

 several times, evaporated and color dried. 



//.//./, //.s: < hlorin, bromin, and iodin found in color qualitatively. (Mulliken 

 " Identification of ( )nranir < ompounds," p. 13). Determination of bromin and iodin 



uasch and Aschotf methKl gave 17 per cent bromin and 9.7 per cent iodin. 

 Volor a mixture of eoein colors containing chlorin, bromin, and iodin. 



RHODAMIV: 



Contains no bromin or iodin; 0.4 per cent ash; insoluble, even on boiling in caustic 

 potash solution; -p. gr. 1.3. 



Aqueous solution pink; yellow fluorescence, which disappears on warming and 

 reappear.- uii cooling. 



