36 



MILK ANALYSIS 



The ether is evaporated, the residue 

 mixed with a little weak solution 

 of sodium hydroxid, and passed 

 through a wet filter; and when this 

 has drained, the fat is washed ofif 

 and the paper dried. An orange 

 tint shows annatto, which may be 

 confirmed by a drop of solution of 

 stannous chlorid, which makes a 

 pink spot. 



If the curd be colorless, no foreign 

 coloring-matter is in it; if orange 

 or brown, it should be shaken with 

 strong hydrochloric acid in a test- 

 tube. 



If the mass turns 

 blue gradually, 

 caramel is pro- 

 bably present. 

 The whe y 

 should be ex- 

 amined for 

 caramel (see 

 page 64). 



If the mass turns 

 pink at once, an 

 azo-color is indi- 

 cated. 



Thickening Agents. — Several instances of the use of brain 

 matter, dextrin and gelatin have been reported. It is also 

 stated that sugar, starch, and salt have been added. Brain 

 matter is easily detected by microscopic examination; starch 

 by the iodin test; dextrin and sugar by increased polarimetric 

 reading, and the sweet taste of the residue. A solution of cal- 

 cium hydroxid in sirup has been sold under the name "grossin" 

 for thickening cream. It would easily be detected by the high 

 ash. Thickening agents of pectinous nature are now commer- 

 cial articles. The most important of these is agar. 



Gelatin. — Stokes detects the presence of gelatin in cream or 

 milk as follows: 10 c.c. of the sample, 20 c.c. of cold water, 

 and 10 c.c. of acid mercuric nitrate solution (page 30) are 

 mixed, shaken vigorously, allowed to stand for five minutes, and 

 filtered. If much gelatin be present, it will be impossible to 

 get a clear filtrate. A portion of the filtrate is mixed with an 

 equal bulk of saturated aqueous solution of picric acid. If any 

 gelatin be present, a yellow precipitate will be immediately 

 produced. Picric acid will detect the presence of one part of 

 gelatin in 10,000 parts of water. 



Agar (agar-agar) is derived from marine algffi. It forms 

 with water a stiff jelly that does not melt as readily as that from 

 gelatin. 



