MILK SAMPLES. 377 



Preservation of Milk Samples. 



Where any special importance is attached to the analysis of 

 any sample, it is an advantage to preserve the sample for refer- 

 ence and further corroborative analysis. Preservatives are added 

 to effect this. The following substances have been used : 



Alcohol. Allen has suggested adding to the milk to be kept 

 twice its weight of alcohol ; his experience and that of Hehner 

 show that analytical data can be obtained on the preserved milk 

 (making allowance for the alcohol added) which agree with the 

 original sample. The objection to this method is that a large 

 amount of a volatile substance is added, and a correction, the 

 exactness of which depends on the amount of alcohol present, 

 must be made. Milk-sugar and salts are also deposited after 

 some time, and are difficult of complete redistribution. 



Chloroform. When added in the proportion of 1 c.c. to 

 100 c.c. of milk it keeps the milk well for a short time. It has 

 the advantage of dissolving in the fat and keeping the cream in 

 an easily miscible condition. As Babcock and Russell have 

 shown, it does not stop enzymic action ; hence changes in the 

 proteins, due to this cause, proceed as if no chloroform had been 

 added. The correction to be applied is small. For keeping 

 samples for a short period, say ten days, this method is good. 



Ether. This preservative is nearly as good as chloroform ; 

 it is, however, not quite so effective and also it is more 

 volatile. 



Collins recommends a mixture of ether and chloroform of 

 specific gravity 1-032, as it does not affect the specific gravity 

 of the milk. The author has, however, shown that ether and 

 chloroform keep the fat in a liquid condition, and that the specific 

 gravity is lowered by this cause. The estimation of the fat by 

 the Gerber method is too high in the presence of chloroform. 

 ~Terpenes, Thymol, Dichlorophenol, and Salicylic Acid. 

 These keep the milk, but allow the cream to rise to the surface, 

 where it sets in a firm layer and is not easily redistributed. 



Hydrofluoric Acid and Pluoboric Acid. The author has 

 proved that these substances, when added to fresh samples in 

 the proportion of \ c.c. to 100 c.c. of milk, keep them in good 

 condition, and, after a year, analysis gives the same figures as 

 those previously found. They curdle the milk, however, so that 

 the sample must be shaken well to bring the precipitated casein 

 into a fine state of division ; a little of the bottle is dissolved 

 and the ash is thereby slightly increased. The author has found 

 this method to be one of the best. 



Formalin. The addition of formalin has many advantages. 

 A very minute amount of the 40 per cent, solution need be 



