io6 MILK AND DAIRY PRODUCTS PART 



4. Determination of the Freezing Point of Milk. 



J. Winter l in his investigations upon the freezing point of 

 the different fluids of the animal organism found that the 

 freezing point of milk was constant at 0'555 C. with very 

 slight variations. On the addition of water the freezing point 

 approaches nearer and nearer the freezing point of water. 

 Winter proposed that the freezing point of the milk should 

 serve as a test for the presence of added water. It must be 

 noted, however, that the freezing point of milk depends upon 

 the degree of acidity, and the sourer the milk becomes the 

 lower does the freezing point become. Winter considers, in 

 spite of this, that a determination of the freezing point and 

 of the degree of acidity would serve as a simple method for 

 controlling the adulteration of milk with water. 



Although Winter's proposal has not yet found a very extended 

 application the operation, as worked out by him, 2 may fitly find 

 a place here. Where a large number of samples have to be 

 tested they are placed in cylindrical corked vessels in ice- 

 water in order to bring the temperature near to C. 



The samples are taken from the ice-water and placed in a 

 freezing mixture composed of one part of coarse salt and three 

 to four parts of finely-crushed ice. After the thermometer, 

 which is fastened to a stand and is divided inO'Ol C.,has been 

 placed in one of the samples, the milk is stirred with a ring- 

 shaped stirrer until the column of mercury remains still. This 

 temperature is noted and is a little lower than the ordinary 

 freezing point, in the vicinity of which, however, it lies. With 

 distilled water the temperature which is at first given is correct, 

 and denotes the freezing point of the thermometer. 



When a determination of the freezing-point of milk (and 

 solutions in general) is made, the first reading must, however, 

 be corrected. This is done by taking the cylinder out of the 

 freezing mixture and allowing it to gradually become warmer, 

 at the same time keeping it well stirred. If the stirring is 

 done with the right hand and the cylinder held in the left, 

 then the warming is much more rapid, thanks to the heat 



1 Compt. rend, de VAcad. des Sciences, Nov., 1895. 



2 Winter et Parmentier. "La cryoscopie du Lait," Revue Gen. du Lait, 

 Vol. Ill, p. 193, 



