VARIATION IN MILK. 



Monier-Williams gives the table below. 

 TABLE XVI. 



83 



As a practical method it is suggested that the freezing point 

 of a solution of 9-495 grammes of pure cane sugar in 100 grammes 

 of water, which freezes at 0-5345 should be taken in exactly 

 the same way as the freezing point of the milk is determined. 



The freezing points may be determined in a usual freezing- 

 point apparatus, using ice and salt as the freezing mixture, 

 and the temperature of this may be as low as 4, but it is very 

 important that this temperature, the rate of stirring, and the 

 same degree of super-cooling be employed in each experiment. 

 All corrections are thus applied automatically to the milk. The 

 addition or removal of fat has no practical effect on the freezing 

 point, but the freezing-point figure increases as milk gets sour ; 

 so long as the acidity has not reached 25, it does not 

 interfere. The sterilisation of milk produces only a very small 

 variation. Though rather too cumbersome and elaborate for 

 the routine testing of milk, the freezing point gives useful 

 information in doubtful cases, but requires considerable experi- 

 mental skill. 



Electrical Conductivity. Coste and Shelbourn have studied 

 the electrical conductivity of milk, and show that it is only 

 moderately constant, varying from a value of K = 0-0035 to 

 0-0047, and is due chiefly to the chlorides present. Dilution 

 with water lowers the value, but not in proportion to the water 

 added, owing to the dissociation of the salts with dilution, 50 per 

 cent, dilution causing only a diminution of 40 per cent, of the 

 conductivity. As an analytical method of milk control the 

 electrical conductivity is of little use 



