NECESSITY FOR WEIGHING CREAM 317 



to throw down all substances in suspension. An application 



of this principle is seen in the freezing of a shallow muddy pond 

 or lake. The ice will be far cleaner than the water was before 

 the freezing started. The dirt will have concentrated down- 

 ward. When a quantity of milk freezes the solid particles are 

 concentrated largely into the center, the outer portion being 

 more largely the water part of the milk. The effect of such is 

 the partial formation of the curd into flakes. These floating 

 particles interfere considerably with the taking of an accurate 

 sample. To obtain a true sample it may even be necessary to 

 weigh out 18 grams of the thoroughly warmed and poured sample 

 into the test bottle rather than to measure it with a pipette. 



Testing Cream: Sampling (Figs. 108 and 109). — ^Cream 

 varies so greatly in fat content and in its fluid properties and 

 mixes with such difliculty compared with milk that much greater 

 care is required to be exercised in obtaining an accurate sample. 

 Cream will rise on cream to such an extent that the top of a can 

 may test 35 per cent fat while the bottom contains only 10 or 

 even 5 per cent fat. In order to obtain a sample which is at all 

 adequate in determining its value, it is essential that the cream 

 be either thoroughly stirred from the bottom by means of a 

 stirring device consisting of an iron rod fitted with a strong disc 

 at the lower end and by means of which an upward rotary motion 

 in the cream can be effected; or by pouring the cream several 

 times from one can to another. When the cream is thoroughly 

 mixed, a quantity of two to three ounces may be transferred to 

 the sample bottle for future work. 



Composite Samples. — Although sufficiently accurate work 

 may readily be done from composite samples of milk the system 

 is not to be recommended for cream. This is chiefly due to the 

 great variation in fat content of the cream, and also to the vary- 

 ing amount which is usually taken to market. 



Necessity for Weighing Cream. — The Babcock test is based 

 upon the use of eighteen grams of sample or some known fraction 

 thereof. Since butter fat weighs only about 87 per cent as much 

 as milk serum and since the fat content of cream will vary all 

 the way from 12 to 50 per cent it is evident that vidth the various 



