PHYSICAL AND CHEMICAL EXAMINATION OF MILK 



185 



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nesium oxid 100 c.c. of the filtrate from the tannin and salt solu- 

 tion. The distillate is received in standard acid and the ain- 

 monia determined as before. The peptones are calculated by sub- 

 traction of the ammonia nitrogen from the combined nitrogen 

 from all other nitrogen compounds. 



Volumetric Methods of Estimating Casein in Milk. — Since the 

 Babcock test for fat has been eminently successful in showing 

 the butter maker the value of milk and cream for butter making, 

 it has seemed desirable to work out a test which gives the cheese 

 maker equally reliable information as to the 

 content of casein in milk. It has been shown 

 that the fat content of milk does not always 

 bear a definite relation to the casein, so a test 

 for fat is not a reliable guide for cheese makers. 

 Although the casein content rises when the 

 fat content rises the proportion of increase is 

 not the same, and cheese makers have ob- 

 served that a milk rich in fat may yield less 

 cheese than poor milk, other conditions being 

 equal. It is true that mixed milk rich in fat 

 yields a cheese of better quality than does 

 poor milk; therefore a test for fat is of con- 

 siderable value in estimating the suitability 

 of a certain milk for cheese making. On the 

 other hand, the variability in the relation of 

 fat to cheese makes a rapid test highly de- 

 sirable. 



Furthermore, by means of the' Babcock 

 test for fat the producer can raise the average 

 fat production of his herd by elimination of 

 poor milk cows, and it is possible that a simi- 

 lar increase in casein content can be obtained 

 if a simple quantitative test for casein be 

 used. 



Several tests have been devised for this 

 purpose. In the following two methods one given by Hart and 

 one by Van Slyke and Bosworth are described. 



The Hart Centrifugal Test.— The principles involved in the test 

 are these: 



"1. Construction of a tube whereon percentages of casein in 

 milk are read directly. These tubes can be purchased (Figs. 66, 

 67). 



"2. Establishment of a proper volume of milk to be used that 

 will conform to the tube and scale adopted, allowing percentage 

 of casein to be read directly. 



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Fig. 66.— Casein 

 tube and cork sup- 

 port. (Bull. 156, No- 

 vember, 1907, Univ. 

 of Wis. Agri. Exp. 

 Sta.) 



