14 



MILK ANALYSIS 



distance below, and the top of the crucible a short distance 

 above, the bend of the siphon. The thimble should be sup- 

 ported by a section of glass tubing, i to 

 2 cm. long, with rounded edges; the edge 

 on which the thimble rests should be a 

 little uneven to prevent a close joint, 

 which would hinder the siphoning of 

 some of the liquid. 



Another method is to use a glass tube 

 open \t both ends, the material to be 

 extracted being held in position by loose 

 plugs of cotton placed above and be- 

 low. 



Loss of solvent by leakage often oc- 

 curs. It may be diminished somewhat 

 by soaking the corks in rather strong hot 

 gelatin solution, draining them quickly 

 and then exposing them for some hours 

 to formaldehyd vapor. 



The solvents most generally employed 

 are ether and petroleum spirit, but car- 

 bon tetrachlorid is well adapted for ex- 

 traction purposes as it has high solvent 

 power for fats and is not easily inflam- 

 mable. 



When extraction is completed, the car- 

 ton and materials may be removed from 

 the tube, and, replacing the parts of the 

 apparatus, much of the solvent may be 

 redistilled into the extractor, thus re- 

 covering the liquid. Care must be taken 

 not to distil the contents of the flask closely or heat strongly, 

 lest some of the more volatile of the dissolved matters pass 

 into the distillate. 



Fig. I. 



