76 Testing Milk and Its Products. 



of fat as delivered to creameries. An average grade of 

 market cream as retailed contains about 25 per cent, of 

 fat. If 18 grams of 25 per cent, cream is measured 

 into an ordinary Babcock test bottle, there will be 

 18 X -25=4.5 grams of pure butter fat in the bottle, 

 or, (since the specific gravity of butter fat is about .9) 

 i^ = 5 cc. It is shown that the space from to 10 

 in the neck of these bottles holds exactly 2 cc. (44). 

 The neck of the milk test bottle is not large enough to 

 show the per cent, of fat in a sample of cream if 18 

 grams are taken for testing, and it is therefore neces- 

 sary to adopt special measures when cream is to be 

 tested. 



86. Errors of measuring cream. Several factors 

 tend to render inaccurate the measuring of cream for 

 the Babcock test, and correct results can therefore only 

 be obtained by weighing the cream. If a 17.6 cc. pi- 

 pette is used in testing the cream, it will not deliver 

 18 grams of crgam, as it will of milk, for the following 

 reasons : 



1. The specific gravity of cream is lower than that of 

 milk; if a certain quantity of milk weighs 1030 Ibs., the 

 same quantity of cream will weigh from 1020 Ibs. to 

 1000 Ibs. or less, the weight being determined by the 

 richness of the cream ; the more fat the cream contains, 

 the less a certain quantity of it, e. g., a gallon, will 

 weigh. 1 



2. Cream is thicker (more viscous) than milk at the 

 same temperature, and more of it will adhere to the 

 sides of the measuring pipette than in the case of milk. 



* For specific gravity of cn-niii of ditTm-nt richness, s-.- tsiblron p. 77. 



