94 Milk and Its Products 
paratus is different from the Babcock test, a much 
higher speed of whirling is used, a smaller sample 
of milk is taken, and the fat is read in a solid 
instead of a liquid form. 
DETAILS OF THE BABOOOK TEST 
The apparatus used in testing milk by the Bab- 
cock method consists of a centrifugal machine, three 
pieces of glassware and commercial sulphuric acid. 
The centrifugal machine.—Many forms of centri- 
fugal machines are in use, almost every manufacturer 
having his own particular style. It is essential that 
the centrifugal should be substantially made; that it 
should ran smoothly and steadily, either loaded or 
empty, and that it should be capable of developing a 
speed of 900 revolutions per minute, with a wheel 
20 inches in diameter. The centrifugals so made 
may be driven either by hand, electric, or steam 
power. In the hand-power machines, the motion is 
transmitted both by belts and by friction cogs; in 
the latter case it is essential that care be taken to 
prevent loss of motion through the friction cogs be- 
coming worn. 
In the centrifugals driven by steam turbines, or 
jets of steam delivered against the circumference of 
the revolving wheel, it is much better that the 
steam be applied at some little distance from the 
revolving bottles, otherwise too great a degree of 
heat may be developed in the machine. Woll has 
shown* that, in those steam turbines in which 
*Hoard's Dairyman, March 9, 1900: vol. 31, p. 75. 
