86 CHEMICAL EXAMINATION 



Annatto. After evaporation of the ether, the fatty residue 

 is made alkaline with caustic soda and, whilst still warm, 

 poured upon a very small wet filter paper. After the solution 

 has passed through, wash the fat from the paper with a stream 

 of water and dry the paper. If, after drying, the paper is 

 coloured orange, the presence of annatto is indicated. This 

 may be confirmed by adding a drop of stannous chloride solu- 

 tion, which, in the presence of annatto, produces a character- 

 istic pink on the orange-coloured paper. 



Aniline Orange. The curd of an uncoloured milk is per- 

 fectly white after complete extraction with ether, as is also 

 that of a milk coloured with annatto. If the extracted curd is 

 distinctly dyed an orange or yellowish colour, the presence of 

 aniline orange is indicated. To confirm this, treat a lump of 

 the fat-free curd with a little strong hydrochloric acid. If the 

 curd turns pink, the presence of aniline orange is assm-ed. 



Aniline orange may also be detected by Lythgoe's method 

 which consists of the addition of 10 c.cms. of concentrated 

 hydrochloric acid to an equal volume of milk in a porcelain 

 dish and imparting a rotary motion to the contents. If any 

 appreciable amount of aniline orange is present, a pink colour 

 is at once imparted to the curd particles as they separate. 



Caramel. If the fat-free curd is coloured a dull brown, 

 caramel is suspected. Shake a lump of the curd with concen- 

 trated hydrochloric acid in a test tube and heat gently. In 

 the presence of caramel the acid solution will gradually turn a 

 deep blue, as will also the white fat-free curd of an uncoloiu-ed 

 milk, while the curd itself does not change colour. It is only 

 when this blue colouration of the acid occurs in conjunction with 

 a brown-coloured curd, which itself does not change colour, 

 that caramel can be suspected, as distinguished from the pink 

 colouration produced by aniline orange under similar circum- 

 stances. 



