98 GRADINC AND TESTING MILK AND CREAM 



The Babcock test always deals with weight. For instance, 

 when we say that a sample of milk tests 4.0 per cen't or that a 

 sample of cream tests 30.0 per cent, we mean that in 100 pounds 

 of the milk there are 4 pounds of fat, or in 100 pounds of the 

 cream there are 30 pounds of fat. 



For the sake of convenience a sample may be measured into a 

 test bottle instead of being weighed, when the accuracy of the 

 result is not likely to be alfected. Milk may be sampled for the 

 Babcock test with a pipette, because the specific gravity of milk is 

 always so nearly the same that the same measure of milk from 

 widely different sources has, for all practical purposes, the same 

 weight, and because milk is in such a liquid condition that it 

 neither holds air nor adheres to the wall of the pipette. Rich 

 cream, on the other hand, has a lower specific gravity than thin 

 cream; moreover, cream is so s>Tupy or viscous in its nature that 

 it will hold air or other gas and stick to the wall of the pipette. 

 For these different reasons, the authors wish to state emphat- 

 ically, that when cream is tested for commercial purposes, as at a 

 creamery, it should never be measured but always weighed into 

 the test bottle. The measuring of cream for the Babcock test, 

 when this test is made for commercial purposes, is a fraudulent 

 practice; and in most of the States and Provinces of the United 

 States and Canada there are laws prohibiting it. 



In taking the sample for a Babcock test of milk a 17.6 c.c. 

 pipette is used. This will deliver 18 grams of milk, the quantity 

 for which the scale on the test bottle is graduated to read per 

 cent of fat. To this we add 17.5 c.c. of sulphuric acid (specific 

 gravity i. 82-1. 83), varying the quantity to suit the strength. 

 The contents are then thoroughly mixed by giving the bottle a 

 rotary motion. The acid acts upon and digests all the solids of 

 the milk, excepting the fat, and heals the sample to a desirable 

 high temperature. The bottle is then placed in the centrifugal 

 tester and whirled for five to six minutes, at a speed suitable 

 to the diameter of the machine, usually 800 to 1000 revolutions 

 per minute. The bottle is then filled to the bottom of the neck 

 with hot water (soft or distilled) and whirled for about two min- 

 utes. A second addition of hot water is then made to float the 



