14 QUAI^ITATIVE EXAMINATION OF MILK. 



it in an evaporating dish lo to 12 cm. in diameter. 

 The glass rod with the adhering fat is placed in the dish. 

 The butter sample is again weighed, and in this way the 

 exact amount of butter-fat taken may be found. One 

 now adds to the butter-fat 50 c. c. of alcohol and one to 

 two grams of pure potassium hydrate. The whole is 

 gradually warmed on a water bath, when the butter-fat, 

 especially when stirred, quickly dissolves to a clear, yel- 

 low fluid, and a strong odor of butyric acid ester be- 

 comes noticeable. The heating is continued for about 

 five minutes, and distilled water is then added, drop by 

 drop. If a cloudiness due to undecomposed fat be no- 

 ticed, continue to warm it until at last the addition of 

 water to the fluid does not produce the least turbidity. 

 The saponification is then completed. If, through care- 

 less addition of water, the fat separates out on the surface 

 as oily drops which will not dissolve in the diluted alco- 

 hol, it must be evaporated to dryness and then redis- 

 solved in alcohol. In such cases it may be better to com- 

 mence the process again with fresh material. If the 

 diluting with water is carefully done, it is very i-are that 

 a separation of oil occurs. 



The clear soap solution is put on the water bath to 

 drive off the alcohol and evaporated to a consistency of 

 syrup. The dish is then removed from the bath and the 

 contents dissolved in 100 to 150 c. c. of water. To de- 

 compose the soap, add to this clear fluid a slight excess 

 of dilute sulphuric acid or hydrochloric acid. In this 

 way the insoluble fatty-acids are precipitated out as a 

 curdy mass, which to a great extent rises rapidly to the 

 surface. The material is heated for about half an hour, 

 until the acids melt to a clear oil and until the watery 

 fluid beneath becomes perfectly clear. 



In the meantime, select a very thick Swedish filter, 

 10 cm. diameter, and dry it in the water oven. The filter 



