80 QUESTIONS AND ANSWERS 



fectly white after complete extraction with ether, 

 as is also that of milk colored with annatto. If the 

 extracted fat-free curd is distinctly dyed an orange 

 or yellowish color, aniline orange is indicated. To 

 confirm the presence of this color, treat a lump of 

 the fat-free curd in a test tube with a little strong 

 hydrochloric acid. If the curd immediately turns 

 pink, the presence of aniline orange is assured. 



4. Lythgoe's test for aniline orange is as follows: 

 Treat about 10 c. c. of the milk with an equal 



volume of hydrochloric acid (specific gravity 1.20) 

 in a porcelain casserole and give the dish a slight 

 rotary motion. If an appreciable amount of aniline 

 orange is present, a pink color will at once be im- 

 parted to the curd particles as they separate. 



5. Detection of caramel (in the curd). If the 

 fat-free curd, after extraction with ether, is colored 

 a dull brown, caramel is to be suspected. Shake 

 a lump of the curd with strong 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 un- 

 colored milk, while the curd itself does not change 

 color. It is only when this blue coloration of the 

 acid occurs in connection with a brown curd, which 

 itself does not change color, that caramel is to be 

 suspected, as distinguished from the pink colora- 

 tion produced at once under similar conditions by 

 aniline orange. 



Name several of the preservatives that are some- 

 times used in milk. 



1. Peroxides. 



2. Borax and boric acid. 



