442 



THE ACIDITY OF MILK, 



The number of milks that have been estimated in Sydney has 



been large, and only a consecutive number are recorded in 



Table iv. 



Table iv. 



Milk. 



Acidity. 



Milk. 



Acidity. 



1 



14° 



9 



16° 



2 



20° 



10 



13° 



3 



18° 



11 



14-5° 



4 



19-2° 



12 



16-4° 



5 



15° 



13 



15-2° 



6 



15° 



14 



14-8° 



7 



18-8° 



15 



13-6° 



8 



17° 







These figures cannot be compared with those in the other Tables, 

 since it is not known how old the samples were. In some cases 

 in which the source was known the acidity was higher (18° to 

 20°) than in country milk (12° to 15°). 



It is interesting to note that the acidity of milk bought in 

 Sydney does not alter for some hours even when kept at a tem- 

 perature of 37° C. Thus, one sample giving an acidity of 16° at 

 9.30 a.m., showed no alteration at 12.40 p m.; and at 5.40 p.m., 

 after 5 hours in the water bath at 37° C, gave the same figure 

 upon titration. In some cases the acidity commenced to rise 

 towards the end of 6 hours' incubation. 



As mentioned previously, the acidity of the milk was at first 

 ascribed to lactic acid. This view became untenable when it was 

 found that CaC0 3 even after hours failed to greatly reduce the 

 acidity. In a sample of milk of acidity 17*6°, after some hours 

 contact with CaC0 3 at 70° C the acidity was 16°. In this 

 sample the lactate was directly estimated and was found to be 

 equivalent to only 0-25 c.c. ~q NaOH for each 100 c.c. milk. 



Samples of milk of known acidity have been filtered through 

 Chamberland niters under a pressure of 4 atmospheres. The 

 filtrate is perfectly clear with a faint yellow tinge when viewed 

 in quantity by reflected light. The acidity of the filtrate 



