114 GRADING AND TESTING MILK AND CREAM 



layer is within about one-fourth of an inch of the stopcock and 

 repeat the operations in this paragraph. 



" VI. Freeing the Fat from the Acid Solution. The fat will 

 now be in a clear transparent layer free from curd, and the solu- 

 tion below it will be practically colorless. To separate these two 

 draw off the latter until the fat nearly reaches the stopcock and 

 centrifuge another minute. Now allow the fat to come down 

 through the stopcock till it just reaches the end of the capillary 

 stem. This last step offers no difficulties, providing the stopcock 

 is kept in control, but it requires care. If desired, the acid may 

 be colored with methyl orange. 



" VII. Determining the Percentage of Fat. Carefully dry 

 the separatory funnel on the outside with a clean soft cloth and 

 weigh it. The weight thus obtained minus ihe weight of the 

 empty funnel represents the weight of butter-fat in 20 grams of 

 the sample. The percentage is obtained by multiplying by 5. 



" Often it is possible to obtain a clear fat layer with but one 

 addition of acid, but in some cases it will be found necessary to 

 add it the second time, as directed. The test for fat alone 

 involves 4 centrifugings of one minute each. The centrifuge 

 should be kept warm and the contents of the funnel in a melted 

 state when the acid is added. The time consumed should not be 

 longer than it takes to test cream with the Babcock test, and the 

 operations involved are simple and easily learned. No difficulty 

 will be experienced in obtaining a clear fat. Occasionally there 

 will appear a slight emulsion at the bottom of the fat layers 

 when the fat is drawn into the stem. This is so small in amount 

 that it does not seem to affect the accuracy of the test to any 

 considerable extent. The emulsion should be weighed as fat and 

 considered as such. 



CLEANING THE SEPARATORY FUNNELS 



" The separatory funnels should be washed after each deter- 

 mination, but it is not necessary to dry them before use, providing 

 their weight, when clean and dry, has been found. The cleaning is 

 easily done with hot water and either soap or cleansing powder. 

 They should be well rinsed off with clean water and drained." 



