i MILK 21 



aldehyde as a preservative. Generally a 40 per cent, solution is 

 employed, which is known commercially as formalin ; 1 c.c. of 

 this is sufficient to preserve a litre of milk for a long time. For 

 smaller quantities of milk it will be found that 50 c.c. are 

 adequately preserved by one drop of formalin. 



Formaldehyde, however, renders the protein substances in the 

 milk very difficultly soluble, and this is of disadvantage in estimat- 

 ing the fat by Gerber's method. The undissolved protein forms a 

 plug below the column of fat in the butyrometer, and makes an 

 exact reading difficult. This condition only arises, however, if 

 relatively large quantities of formalin (5 per thousand or more) 

 are used. 



Before the bottle containing a sample of milk which is to be 

 investigated is opened, it must be repeatedly shaken to mix the 

 cream, which has separated on the surface, with the milk below. 

 If this is not easy to do, then the bottle should be warmed to 

 40 C. in a water-bath, after which the two liquids in the bottle 

 will quickly mix on shaking. The bottle should then be opened 

 and the contents emptied into a large clean beaker ; if any cream 

 is left adhering to the inside of the bottle the milk must be 

 poured back again, and the bottle shaken until no traces of 

 cream are to be seen. Immediately before taking a known 

 quantity of milk by means of a pipette, the contents of the 

 beaker should be poured into another clean, dry beaker, and 

 back again, to ensure a thorough mixing. When no preservative 

 has been added to the sample of milk it often happens that it 

 arrives for investigation in a sour or coagulated condition. The 

 following method, proposed by Dr. M. Weibull, 1 of Alnarp 

 (Sweden), can then be employed, and it serves also in the 

 investigation of samples of sour buttermilk. 



The milk which has become sour is not poured from the 

 bottle, but a rough estimate is made of the quantity which is 

 there. Suppose that the estimated amount be taken as 200 c.c. ; 

 to this 20 c.c. of ammonia, that is, 10 percent, of the sour milk, 

 is then added from a burette, the cork replaced, and the bottle 

 thoroughly shaken until the coagulated material dissolves in 

 the ammonia. The result ought to be a homogeneous, slightly 

 opaque liquid. The contents of the bottle are then emptied 



1 K(jl. Landtlruks-Akad. Handl. o. Tidxkr., 1894, p. 243 ; Milch-Zcitung, 

 1894, pp. 247 and 413. 



