42 MODERN METHODS OF TESTING MILK 



attached. The smaller the wheel, the greater must be 

 the number of revolutions a minute. 



Farrington and Woll have prepared the following 

 able, showing the necessary number of revolutions for 

 different sizes of testers: 



DIAMETER OF No. of revolutions 

 WHEEL IN INCHES of disc per minute 

 10 1074 



12 980 



14 909 



16 848 ' 



18 800 



20 759 



22 724 



24 693 



In the case of steam-turbine testers, they are, or 

 should be, made to run at the desired speed under a 

 definite head of steam. These testers should always 

 be provided with a pressure-gage, and a speed-indi- 

 cator is also desirable. 



In the case of hand-testers, the speed can be ascer- 

 tained in the following manner: Give the handle one 

 full turn and count the number of times a given point 

 on the disc goes round. Suppose, for example, that 

 the diameter of the disc is 16 inches and that it revolves 

 14 times for one turn of the handle. Such a disc ought 

 to revolve 848 times per minute according to the pre- 

 ceding table. The handle must be turned around as 

 many times a minute as 14 is contained in 848 in or- 

 der to attain the desired speed, which is found to be 

 about 60 times, or once a second. Then, with watch 

 in hand, regulate the turning of the handle until it 



