Chemical Analysis of Milk and Its Products. 241 



back and forth repeatedly from a small warm beaker 

 into the flask, and the quantity wanted is then drawn 

 off with a warm pipette. 



281. Specific gravity. This is generally determined 

 at 100 C. The method of procedure is similar to that 

 described under milk (248). The picnometer (capacity 

 about 25 cc.) is filled with dry filtered butter fat, free 

 from air bubbles; the fat is heated for 30 minutes in a 

 beaker, the water in which is kept boiling. On cooling, 

 the weight of picnometer and fat is obtained, and by 

 calculation as usual, the specific gravity of the fat. 



The specific gravity of pure natural butter fat at 

 100 C. ranges between .8650 and .8685, while artificial 

 butter fat (i. e., fat from other sources than cow's milk) 

 has a specific gravity at 100 C. of below .8610, and gen- 

 erally about .85. 



282. Reichert-MeissI method (Volatile Acids.) 5.75 

 cc. of fat are measured into a strong 250 cc. weighed 

 saponification flask, by means of a pipette marked to 

 deliver this amount, and the flask when cool is weighed 

 again. 20 cc. of a glycerol-soda solution (20 cc. of 

 soda solution (1 : 1) to 180 "cc. of pure glycerol), are then 

 added to the flask and the flask is heated over a naked 

 flame or hot asbestos plate until complete saponification 

 has taken place, as shown by the mixture becoming per- 

 fectly clear. If foaming occur, the flask is shaken 

 gently. 



135 cc. of recently-boiled distilled water are now 

 added, drop by drop, at first, to prevent foaming, and 

 when the solution is clear, cooled to about 70 C. ; 5 cc. 

 of dilute sulfuric acid (200 cc. cone. H 2 S0 4 per liter) are 



16 



