PRESERVATION OF MILK 



385 



phenolphthaline than when quite fresh). When the differences 

 of time are calculated the following table is obtained : 



Table of Additional Time which Milk will keep sweet when 

 Preservatives are added. 



Eichmond adds : " It is assumed that to be of any appreci- 

 able use, preservatives should increase the " life " of the milk 

 by 12 hours at 80 to 90 (hottest summer temperature), and 

 on this basis 0'09 per cent boric preservative and 0'004 per 

 cent formaldehyde are the minimum amounts necessary in 

 summer." 



Rideal, 1 taking 0*25 per cent lactic acid as the maximum 

 acidity allowable, found that 1:2000 boric acid and 1 : 50,000 

 of formaldehyde kept milk sweet for the 23 hours of the 

 experiment at as high a temperature as 24 C. (75*2 F.). 



Price 2 found that formaldehyde added to milk in the 

 proportion of 1 : 20,000 prevented the development of the 

 more commonly met with bacteria in milk, and when added in 

 the proportion of 1 : 1560 killed them. 



It is not, however, satisfactory to take the amount of 

 lactic acid produced as a reliable index of the bacterial changes 

 taking place. It is quite possible, and does take place to a 

 certain extent, that while the lactic acid bacilli may be 

 inhibited other bacteria may be much less affected. For 



1 Departmental Committee Report, 1901, p. 400. 

 2 Centralbl.f, Bakt. Abt. 2, 1905, xiv. p. 65. 



2c 



