58 Testing Milk and Its Products. 



before is taken, viz., 800 revolutions for an 18 inch tester (radius 

 9 inches); then if x designate the radius of the tester and y the 

 speed required, we have 



xy 2 =9x800 2 , or 

 -, X 800* 



The figures obtained by the use of this formula are similar to 

 those given in the preceding table. 



67. To find the number of turns of the handle corres- 

 ponding to the number of revolutions made by the wheel, 

 the handle is given one full turn, and the number of 

 times which a certain point or part of the wheel revolves, 

 is noted. If the wheel has a diameter of 20 inches, and 

 revolves 12 times for one turn of the handle, the latter 

 should be turned \* =63 (see table), or about once every 

 second, in order to affect a maximum separation of fat. 

 By counting the number of revolutions, watch in hand, 

 and consulting the preceding table, the operator will 

 soon note the speed which must be maintained in case of 

 his particular machine. It is vitally important that the 

 required speed be always kept up; if through careless- 

 ness, worn-out or dry bearings, slipping belts, etc., the 

 speed is slackened, the results obtained will be too low; 

 it may be a few tenths, or even more than one per cent. 

 Care as to this point is so much the more essential, as the 

 results obtained by too slow whirling may seem to be all 

 right, a clear separation of fat being often obtained even 

 when the fat is not completely separated. 



68. Ascertaining the neccessary speed of testers. In 

 buying a tester the operator should first of all satisfy 

 himself at what speed the machine must be run to give 

 correct results: the preceding table will serve as a guide 



