28 CHEESE MaxkIna. 
fectly liquid condition. The fat should be read off at a tem- 
perature of about 140° F. Better results may be obtained by 
first filling water up to the neck and whirling, and then bring- 
ing the fat into the neck by a second filling prior to the final 
whirling. 
Several precautions should be observed to get uniformly 
clear readings and reliable tests. 
58. Strength of Acid. 
First, the acid should be commercial sulphuric acid of a 
specific gravity of 1.82 to 1.83. If too strong the fat will be 
charred and black specks will be found in the fat column. If 
too weak, there will be white matter with the fat. Dairy supply 
houses furnish a hydrometer for testing the specific gravity of 
the acid. If it is 1.81 it is too weak, and if over 1.83 too strong. 
If the acid is only a little too strong cr too weak, the difficulty 
can be obviated by using a little more or a little less, as the case 
may require. One should observe the color of the fat. It ought 
to be a deep straw or yellow color. If white or light colored the 
acid is weak; if black it is too strong. As a general rule, there 
is little difficulty in getting good acid. Both milk and acid 
should have a temperature of about 70° when tests are made. 
Automatic acid measures can be obtained from supply 
houses which may be used for filling the bottles with the right 
amount of acid. The test bottles should be shaken one at a time 
and not in a tray, as in that case the milk in some bottles may 
not be thoroughly dissolved. 
The acid should go to the bottom of the bottle without mix- 
ing much with the milk before the final shaking. If it mixes 
partially and then is allowed to stand, a portion of the milk will 
be acted upon too strongly by the acid, with the result that the 
fat will be charred and black specks will be found in the fat 
column. 
59. Speed of the Centrifuge. 
The speed of the ordinary tester, which is about eighteen 
inches in diameter, should be about one thousand revolutions 
per minute. The fat is forced to the top of the liquid by the 
centrifugal force, and unless this is sufficient all the fat will not 
be separated. If the speed is too great the bottles may be broken 
