86 CHEMICAL EXAMINATION 



Annatto. After evaporation of the ether, the fatty residue 

 is made alkaUne 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 assured. 



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 uncoloured 

 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 

 coloiu-ation produced by aniline orange under similar circum- 

 stances. 



