ON MILK AND MILK-TESTING 75 



If a sample of milk contained 8.5 per cent of solids 

 not fat and 3.3 per cent of fat, should it be con- 

 sidered as adulterated? 

 If one -should learn that the milk was produced 

 by a herd of Jersey cows, it should be considered 

 adulterated. In that case the composition of the 

 original milk would be at least 4.4 per cent of fat 

 and 8.8 per cent of solids not fat. Those figures 

 could be used as a basis for computing the kind and 

 amount of adulteration. If the milk was produced 

 by a Holstein herd, there would be the possibility 

 that it was adulterated only in the sense that a 

 herd of cows was selected which gave a low grade 

 of milk, thus bringing the quantity of total solids 

 below the legal standard of 12 per cent. If such 

 milk was sold and no information could be gained 

 regarding the character of the herd producing it, 

 then it would be considered as having been actually 

 adulterated. 



What is the Hart casein test? 



It is a method of testing milk for the percentage 

 of casein it contains. 



Upon what principles is the Hart casein test based? 



1. That dilute acetic acid coagulates casein in an 

 insoluble form heavier than the milk serum. 



2. The ability of chloroform to extract the fat 

 from the precipitated casein and form a solution 

 heavier than the milk serum or coagulated casein. 



3. Adopting a graduated tube and a volume of 

 milk so that the volume of collected casein indicates 

 on the scale the percentage of casein in the milk. 



