PRESERVATION OF MILK 



3^S 



phenolphthaline than when quite fresh). When the differences 

 of time are calculated the following table is obtained : 



Taile of Additional Time which Milk will heef 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,^ 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 



^ Departmental Ooniinitlee Report, 1901, p. 400. 

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



