PHYSICAL AND CHEMICAL EXAMINATION OF MILK 155 



for three to four days before using. During tiiis time the solu- 

 tion should be shaken occasionally. It is ready for use when foam- 

 ing has ceased. 



If the sample of milk cannot be tested when fresh a preserva- 

 tive must be added. The preservative is prepared by dissolving 

 70 grams pure potassium bichromate in 312.5 c.c. of strong am- 

 monia and 1000 c.c. of water. 



Several methods are known by which the fat is determined 

 volumetrically by use of strong chemicals and centrifugal force. 

 The desirabiUty of a rapid method for determining the fat content 

 of milk became apparent with the rapid development of co-opera- 

 tive dairying. The producer was paid by weight or volume of 

 milk delivered to the creamery, and the milk from herds produc- 

 ing rich milk was of the same pecuniary value as milk with low 

 fat content, in spite of the fact that rich milk yields a higher per- 

 centage of butter-fat than does poor milk. Producers of rich 

 milk felt justified in demanding a higher price. 



This led to the working out of rapid methods of fat determina- 

 tion, which also rendered watering of milk unprofitable. Of the 

 several methods designed to serve the purpose, the Babcock 

 method is most generally employed in this country. It was in- 

 troduced in 1890, and although other methods are used in some 

 countries, they are modifications of Babcock's original method. 

 In all these tests the casein is dissolved by the use of strong acid 

 or alkah or alkaU mixed with sodium sulphate, potassium-sodium 

 tartrate, or salts of citric and salicylic acids. 



The Babcock method is practically the only one of these used 

 by practical dairymen in this country, and its detailed considera- 

 tion is, therefore, of the utmost importance. An interesting 

 account of its development is given in the Wisconsin Circular No. 

 32, entitled "The 'Coming of Age' of the Babcock Test." In this 

 circular the Babcock test is called the "Founder of Modern Dairy 

 Education." This simple test has done more than any other single 

 factor to reduce the watering of milk; it has shown the producer 

 how to learn the exact productivity of each individual animal, 

 thus enabhng him to weed our poor producers and replace them 

 with good milk cows. It has shown sources of loss to butter and 

 cheese makers; it has placed the pecuniary value of milk on a 

 logical basis, and finally the dairyman can learn through this test 

 whether his separator is working to best advantage by determina- 

 tion of the fat in the skimmed milk. 



The principles involved in the Babcock test for butter-fat 

 are: 1, The complete solution of colloids in milk by action of 

 strong sulphuric acid; 2, the production of sufficient heat by the 

 mixture of acid and milk to completely liquefy the fat, and 3, 



