148 



MILK 



then evaporated from the flask, the exact weight of which is 

 known, and the difference determined by weighing. From the 

 weight of the fat in the flask the percentage is calculated. Traces 

 of fat may remain in the paper coil even when extraction is con- 

 tinued for six to eight hours. In place of filter paper fat-free 

 thimbles made of filter paper can be procured and used for fat 

 extraction. 



Another method of determining the fat content of milk by 

 ether extraction is the one of Werner-Schmidt (Leach) as follows: 

 Ten c.c. of milk are measured, or, better, 10 grams weighed, 

 placed in a test-tube of 50 c.c. capacity and 10 c.c. of hydrochloric 



o 



Fig. 40 — Soxhlet ether extractor. 



acid added. After shaking, the mixture is boiled over a flame for 

 a few minutes or placed in boiling water for about ten minutes. 

 The tube is then cooled and 30 c.c. washed ether added. A stop- 

 per with two glass tubes is used to close the tube. One of the 

 glass tubes reaches just below the stopper, the other one reaches 

 farther down and is bent up at the end. After thorough shaking 

 of the acid-milk mixture the ether is allowed to form a layer on 

 the surface. The bent glass tube is moved down into the ether 

 until the opening of the curved end is just above the surface of 

 the acid-milk mixture. The ether is then blown into a tared flask 

 or beaker. The process is repeated twice, using 10 c.c. of ether 



