TESTING BUTTER 643 



within one-fourth of an inch of the stopcock and repeat the opera- 

 tions 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 solution 

 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. 



VII. Determining the Percentage of Fat. "Carefully dry the 

 separatory funnel on the outside with a clean soft towel and weigh it. 

 The weight thus obtained minus the weight of the empty funnel 

 represents the weight of butterfat in 20 grams of the sample. The 

 percentage is obtained by dividing this weight by 2 and multiplying 

 by 10. 



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

 addition of acid, but in the majority of cases it will be found neces- 

 sary to add it the second time, as directed. The proportion of acid 

 and water selected is the outcome of a number of experiments, and 

 is the one that yields the best results. The test for fat alone involves 

 4 centrifugings of 1 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 much longer than it 

 takes to test cream with the Babcock test, and the operations in- 

 volved are simple and easily learned. No difficulty has been experi- 

 enced in obtaining a clear fat. Occasionally there will appear a 

 slight emulsion at the bottom of the fat layer 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 determination, 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." 



Comparative tests by Shaw show that this test yields results 

 which compare very closely with those of the official fat estimation. 

 The test can be completed in 20 minutes. 



