220 Testing Milk and Its Products. 



tion of natural butter, or give satisfactory results only in 

 the hands of experts. The Reichert-Wollny method 

 given in detail below is the standard method the world 

 over, and the results obtained by it are accepted in the 

 courts. 



271. Filtering the butter fat. The butter to be exam- 

 ined is placed in a small narrow beaker and kept at 60 

 C. for about two hours. The clear supernatant fat is 

 then filtered through absorbent cotton into a 200 cc. Erlen- 

 meyer flask, taking care that none of the milky lower 

 portion of the contents of the beaker be poured on the 

 filter. In sampling the butter fat, it is poured back and 

 forth repeatedly from a small warm beaker into the 

 flask, and the quantity wanted is then drawn off with a 

 warm pipette. 



272. Specific gravity. This is generally determined at 

 100 C. The method of procedure is similar to that de- 

 scribed 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 cal- 

 culation 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 cows' milk) has a spe- 

 cific gravity at 100 C. of below .8610, and generally 

 about .85. 



273. Reichert-Wollny method (Volatile Acids). 5.75 cc. 

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

 fication flask, by means of a pipette marked to deliver 



