114 MODERN METHODS OF TESTING MILK 



tion in the case of samples of a given weight and at a 

 definite temperature. 



Loss by sputtering. When butter is heated very 

 rapidly, the sudden escape of water-vapor is liable to 

 cause sputtering, throwing some of the material out 

 of the evaporating-dish and thus causing too high- re- 

 sults. This is apt to happen when the dish is heated 

 over a high gas flame. The use of an alcohol lamp or 

 the interposition of a piece of thin asbestos or iron 

 plate over the flame obviates this difficulty. Sputtering 

 may also occur in a high-pressure oven if the temper- 

 ature is too high during the first part of the process. 



ASCERTAINING THE AMOUNT OF WATER 

 EVAPORATED 



In most methods the amount of water evaporated 

 is found by subtracting the weight of the cooled dish 

 and contents after heating from the weight of the dish 

 and contents before heating; the weight lost during 

 heating represents the amount of water in the butter. 

 The cooling and weighing should be done in a room 

 where the air is 'fairly dry. In some methods, the 

 evaporated water is condensed in a graduated tube 

 and measured directly. 



CALCULATION OF PERCENTAGE OF WATER IN 

 BUTTER 



In the case of those methods which condense the 

 evaporated water, the percentage of water in the butter 

 tested is read directly from the graduated tube. When 

 the water is evaporated into the air and its amount 

 determined by the weight lost, the percentage is cal- 

 culated as follows: Divide the loss of weight by the 



