19 



modifications that must be observed. The range of fat in 

 cream, and consequently the specific gravity, is much 

 greater than in milk, so that 17.5 cubic centimeters do not 

 necessarily represent 18 grams, as in the case of milk. 

 Cream also varies in consistency, some being thin and some 

 thick; therefore in some cases much more would adhere 

 to the walls of the pipette than in others. For these rea- 

 sons cream can not be accurately measured. The charge 

 for the test must be weighed into the test bottle. 



Cream-test bottles. The cream-test bottles used in the 

 Babcock test are of various designs. (See figure 16.) 

 Those conforming to the requirements of the United 

 States Bureau of Standards differ from milk bottles only 

 in the graduations and in the length and diameter of the 

 neck. Test bottles are made for both an 18-gram and a 

 9-gram charge. 



Cream-test balances. Several types of balances designed 

 for weighing cream charges are on the market (figs. 17,18, 

 and 19). The small torsion balances prove to be very sat- 

 isfactory if care is taken that the important metal parts 

 are not allowed to rust. Balances should be tested for 

 sensitiveness from time to time and should always be kept 

 in perfect condition. 



Preparing cream for testing. 'The point never to be lost 

 sight of in testing cream or milk is that the small quantity 

 taken for the test must be truly representative. No matter 

 how carefully the test is carried out, if the charge taken 

 does not accurately represent the cream or milk to be 

 tested, the results will be worthless. The preparation of 

 cream for testing does not differ materially from that of 

 milk. The fat must be evenly distributed, and if there are 

 no lumps this can be accomplished by pouring from one 

 receptacle to another, warming the cream slightly if cold. 

 If lumps are present, it has been advised to pass the cream 

 through a fine sieve, rubbing the lumps through with the 

 fingers and then mixing as usual. If the cream has stood 

 for some time in the sample jar, the top may have become 

 hard, leathery, and difficult to remove. In this case, the 

 jars should be set in warm water until the contents have 

 reached 100 to 110 F., when the cream will be soft and 

 can be easily removed. 



