Acidity of Milk. 



It is to be regretted that the bacterial catalase cannot be 

 separated from the original catalase, so that it would be possible 

 to draw definite conclusions from the catalase findings of market 

 milk, as to whether the catalase quantities which are demonstrated 

 were present in the freshly drawn milk or whether they have been 

 subsequently formed by bacterial growth. Wolf claims that milk 

 which reduces slowly and shows a strong catalytic property by 

 the formation of large quantities of oxygen should be suspected 

 of containing secretions from animals with affected udders. It 

 would be impossible to draw conclusions based on this statement 

 in those cases where rapid reduction occurs coincidently with 

 strong catalytic action. 



Degree of Acidity. 



In discussing the original properties of milk it was mentioned 

 that casein, acid salts of milk, carbonic acid, etc., give to milk an 

 acid reaction to phenolphthalein. 



Even immediately after milking, in order to produce neutral- 

 ization of the milk against phenolphthalein, several c. c. of sodium 

 hydrate are required. The number of cubic centimeters of a 

 normal Na OH dilution which are needed to neutralize a certain 

 quantity of milk are known as degrees of acidity. The number 

 obtained varies, depending on the method and dilution employed. 



Thus Soxhlet-Henkel, for instance, employed 100 c. c. of milk 

 and 14 normal Na OH and obtained an average value of about 

 6 to 7 degrees of acidity. 



Jensen, who works with TO normal Na OH, uses on an 

 average 18 to 19 c. c. 



Thorner dilutes 10 c. c. of milk with 30 c. c. of water and 

 titrates with TO normal Na OH. 



The degrees of acidity, as determined by Domic, are higher 

 than those of Soxhlet-Henkel : He uses 10 c. c. of milk and alkali 

 which contains 4.445 gm. Na OH to 1000 H 2 0. tV c. c. of alkali, 

 according to Domic, is equal to a degree of acidity. 



Schrott-Fichtl and Domic suggested as an advantage the drop- 

 ping of the "scale of degree of acidity" and employing an alkali, 

 1 c. c. of which would correspond to 0.01 gm. of lactic acid, or to 

 figure the degree of acidity on the basis of lactic acid. Then 

 1 c. c. of TO alkali would correspond to 0.009 gm. of lactic acid 

 and 1 c. c. of *4 normal Na OH=22.5 gm. 



Of course, it should be remembered that the neutralization 

 of the alkali does not correspond entirely to the amount of lactic 

 acid present but depends also on other factors, for instance, on 

 the proportion of acid phosphates, carbonic acid and casein. 



Only the increase in acidity which is obtained by a compara- 

 tive testing of fresh milk and an older sample of the same milk, 

 should therefore be considered as lactic acid, since Henkel proved 

 that free lactic acid is not present in freshly drawn milk. 



