44 DAIRY LABORATORY GUIDE 



will preserve a pint of milk for several weeks. The tablets 

 are very poisonous, and so are colored red and yellow respec- 

 tively, as a safeguard against accidents. 



Churned Milk. It often happens that milk will become 

 partially churned in transit, especially if the container is not 

 completely filled, and the butter-fat will gather in lumps. 

 When this occurs it is well to warm the milk to about 100 F., 

 and hold it there until the lumps of fat are melted and then 

 mix thoroughly by pouring before taking the sample to test. 



Frozen Milk. The water in the milk or cream freezes 

 first, which forces the solids toward the center of the can. In 

 order to get a representative sample, all frozen portions must 

 be thawed out and then the entire contents of the can must 

 be thoroughly mixed before taking the sample to test. 



Sour Milk. The casein in milk coagulates on souring and 

 tends to incorporate the fat globules, which often makes it 

 difficult to secure an accurate sample. In case the sample 

 becomes sour, a small quantity of alkali added to the milk 

 will dissolve the casein sufficiently to enable an accurate sam- 

 ple to be taken. It is well to take a definite quantity of the 

 alkali and in proportion to the size of the milk sample, which 

 will enable a corresponding correction in reading the test. 



How TO CALIBRATE GLASSWARE 



A great deal of the glassware used for testing has not been 

 carefully standardized before leaving the factory, and so is 

 very unreliable. In order to insure accuracy, it is often 

 necessary for the operator of the Babcock test to calibrate 

 the glassware. 



Milk Bottles. 1. Plunger Method. This plan requires 

 the use of a metal plunger made in two parts connected with 

 a wire. Each part is of the proper size to displace 1 c. c. of 



