228 MILK HYGIENE 



until, after thorougli shaking, the milk becomes faintly 

 reddish. Then the exact amount of solution that has 

 been used for neutralization is read off, and the degree 

 of acidity determined. If one has to make many titra- 

 tions it is most convenient to use a burette with a supply 

 from a larger tank; such a titrating apparatus can be 

 procured from any dealer in chemical apparatus. 



[A rapid method for determining the acidity of milk 

 has been devised, which depends on the use of an accu- 

 rately measured amount of alkali dispensed in the form 

 of a tablet. This makes it possible to quickly prepare a 

 standard solution, and the method is very useful for in- 

 spections in the field. If the indicator, phenolphthalin, 

 is included in the tablet, the test is still more convenient. 

 It is made as follows : 



Tablets are dissolved in a measured quantity of dis- 

 tilled water, sufficient to give a solution of standard 

 strength (usually five tablets make 100 c.c. of solution, 

 but this varies with the brand of tablet and the manu- 

 facturer's instructions must be observed) 18 grm. (17.6 

 c.c, being measured in the pipette used for the Babcock 

 test) of milk are measured into a white porcelain cup 

 and the alkali solution is added from a measure (burette 

 or graduated cylinder) until the pink color becomes 

 permanent. The amount of solution used shows the 

 percentage of acid in the sample. 



If a standard of 0.2 per cent, lactic acid has been 

 adopted, then the amount of alkali solution required to 

 show any excess above this limit may be placed directly 

 in the cup and the measured sample of milk added to it. 

 If the pink color remains, there is less than 0.2 per cent, 

 of acid in the sample; if it disappears, there is more 

 than 0.2 per cent, of acid. L. P.] 



Only a few German regulations give a standard for 

 the acid permitted in market milk. Sometimes, the 



