Chemical Analysis of Milk and Its Products. 237 



worthless, in case of samples containing a considerable 

 proportion 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. 



280. Filtering the butter fat. The butter to be ex- 

 amined 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. 

 Erlenmeyer 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. 



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-Wollny 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 



