GERBER'S FAT DETERMINATION 211 



the glass so that it forms a layer upon the surface of 

 the sulphuric acid. Now, exactly 11 c.c. of well m i xed 

 milk that has been heated to 15° C. (60° F.) are measured 

 and poured into the bottle, which is closed by a rubber 

 stopper and then it is well shaken. The milk dissolves 

 with the generation of considerable heat. The stopper 

 is driven in so far that in the inverted bottle, the fluid 



FlO. 21. 



Gerber's apparatus for fat-determination. 



reaches the mark on the scale ; the bottle is put into the 

 centrifuge and this is set in motion, after it has been 

 well balanced. If the sample is not to be centrifuged at 

 once, the bottle should be placed in a water bath at 60° 

 to 65° C. (140° to 150° F.). The process of centrifuging 

 lasts 10 minutes with such a machine as shown in figure 

 21 ; and in order to keep up speed it is necessary to ac- 



