Preserving Milk by Chemicals. 



39 



producing bacteria contained in the milk. If we now 

 try to find ont which bacteria are of the rennet pro- 

 ducing kind, we shall see that they are principally 

 those that live in the uppermost layers of the soil and 

 have been collected with the hay and other fodders, so 

 that we may presume that such milk which has taken 

 up many bacteria in the stable, or which has been 

 strongly polluted after having been drawn, will more 

 rapidly advance toward rennet curdling than milk 

 which has been less infected. 



Among other ingredients used, presumptively, for 

 the preservation of milk are lime, borax, boracic acid 

 and salicylic acid. Some of these are even now used 

 extensively and have been for many years, for in- 

 stance, by the farmers of the North Sea coast, because 

 for them it was a matter of existence to keep their 

 milk sweet for at least thirty hours to enable it to 

 reach their only remunerative market which, to the 

 greater number, was London. 



Investigations on the preserving merits of boracic 

 acid, common salt and salicylic acid show the follow- 

 ing results : 



. Commencement of Acidity 



Admixture. Confirmed by Tasting. 



0.02 per cent, boracic acid after 30 hours 



0.04 

 0.06 

 0.02 

 0.04 

 0.06 

 0.02 

 0.04 



0.06 



Pure milk. 



salt. 



salicylic acid. 



35 

 56 

 36 

 26 

 26 

 33 

 47 



144 



25 



Commencement 

 of Curdling. 



after 47 hours 



" 47 



" 60 



" 30 



" 32 



" 32 



" 58 



" 82 

 was not curdl- 

 ed after 8 days 

 after 28 hours 



