31 



The ether extract, containing the fat and the annatto, if present, is evaporated on 

 the water bath, the residue is made alkaline with sodium hydroxid and poured upon 

 a small, wet filter, which will hold back the fat and, as the filtrate passes through, 

 will allow the annatto, if present, to permeate the pores of the filter. On washing 

 off the fat gently under the water tap all the annatto of the milk used for the test 

 will be found to have been concentrated on the filter, giving it an orange color, tol- 

 erably permanent and varying in depth with the amount of annatto present. The 

 confirmatory test for annatto with stannous chlorid may afterwards be applied to the 

 colored filter, producing the characteristic pink color. 



The fat-free curd, if colored after the ether has been poured off, is examined fur- 

 ther for caramel or analin orange by placing a portion of the curd in a test tube and 

 shaking vigorously with concentrated hydrochloric acid. If the color is caramel, the 

 acid solution of the colored curd will gradually turn a deep blue on shaking, as 

 would also the white fat-free curd of an uncolored milk, the blue coloration being 

 formed in a few minutes if the fat has been thoroughly extracted from the curd; 

 indeed, it seems to be absolutely essential for the prompt formation of the blue color 

 in the aekl solution that the curd be free from fat. Gentle heat will hasten the 

 reaction. It should be noted that it is only when the blue coloration of the acid 

 occurs in connection with a colored curd that caramel is to be suspected, and if 

 much caramel be present the coloration of the acid solution will be a brownish blue. 

 If the above treatment indicates caramel, it would be well to confirm by any of the 

 usual tests on a fresh sample of the milk. If the milk has been colored with anilin 

 orange, the colored curd, on applying the strong hydrochloric acid in the test tube, 

 will immediately turn pink. In the case of caramel, the color of the curd itself 

 remains unchanged, the solution only turning blue, and that gradually; on the con- 

 trary with the anilin orange the curd itself takes the pink color the moment the 

 acid touches it. If a large amount of the anilin orange has been used in the milk, 

 the curd will sometimes show the pink coloration when hydrochloric acid is applied 

 directly to it, before treatment with ether, but the color reaction with the fat-free 

 curd is very delicate and unmistakable. 



Summary of procedure. 



Curdle 150 cc of milk in casserole with heat and acetic acid. Gather curd into one 

 mass. Pour off whey, or strain if curd is finely divided. Macerate curd with ether 

 in a corked flask. Pour off ether. 

 Ether extract: 



Evaporate off ether; treat residue with sodium hydroxid and pour on wetted 

 filter. After solution has passed through wash off fat and dry filter, 

 which, if colored orange, indicates presence of annatto. (Confirm by 

 stannous chlorid. ) 

 Collected curd : 



(1) If colorless, indicates presence of no foreign color other than in ether extract. 



(2) If orange or brownish, indicates presence of anilin orange or caramel. 



Shake curd in test tube with concentrated hydrochloric acid. 



(a) If solution gradually turns blue, indicates caramel. (Confirm by 



testing for caramel in whey of original milk. ) 



(b) If orange curd immediately turns pink, indicates anilin orange. 



To differentiate the azo dyes included under the term ''anilin orange," dye a 

 piece of wool in the acid solution, extract the dye from the wool with ammonium 

 hydroxid, and apply the tests as indicated in the table on page 34, headed "Coal- 

 tar colors." 



a Note bv the writer. 



