180 XOEMAL MILK : ITS ADULTERATIONS, ETC. 



Table XLIV. gives the average amount of acidity above the 

 normal acidity of milk developed in the times stated at various- 

 temperatures (see also Fig. 14, p. 135). 



The rate of souring increases 1 '5 times for a rise of 10° F. in 

 temperature, or 2-075 times for a rise of 10° C. 



When milk reaches an acidity of 13° above the normal it 

 curdles on boiling, and at 65° it curdles spontaneously; the 

 times taken to reach these points are : — 



Acidity. 

 13°, . 

 65°, . 



It is seen that lowering of temperature has an immense influ- 

 ence on the life of milk. 



Boric acid preservatives are used in quantities varying from 

 0"01 up to G'3 per cent. 



The following figures show the amounts used : — 



Up to 0-03 % in 45 % of samples containing boric preservative. 



From 0-03 to 0-06 „ 27-5 

 Above 0-06 „ 27-5 



In the bulk of the samples the quantity added was insufficient 

 to have any really useful efiect in hot weather. 



Formaldehyde appears to be added in proportions varying 

 from 0'002 to 0'005 per cent., and only the larger quantities 

 would be really efficient as preservatives. 



To sum up, it appears that to be of any real use in hot weather 

 at least O'l per cent, of boric preservative, or 0'004 per cent, of 

 formaldehyde is necessary, and even then the effect is only equal 

 to that produced by cooling down the milk about 10° F. ; the 

 cost of cooling is approximately the same as the cost of preserva- 

 tives, and so far as milk is concerned, there is absolutely no justi- 

 fication for the use of preservatives ; the practice appears to be 

 dying out. 



Objections. — The practice of adding preservatives is by 

 many considered highly reprehensible, while others are warmly 

 in favour of this course. Evidence that any well-marked 

 injuiious effect follows the consumption of milk containing 

 small amounts of preservatives is not forthcoming. 



Wiley, as the result of an exhaustive experiment extending 

 over many weeks, concludes that both boric acid and borax, 

 when continuously administered in small doses for a long period, 

 or when given in large quantities for a short period, create dis- 

 turbances of appetite, of digestion, and of health. 



