316 MILK AND MILK PRODUCTS. XIV. 



the fat globules, liquid at the temperature of the cow, do not 

 at once solidify on cooling, but remain for some time in a 

 super-cooled liquid condition. Since contraction occurs when 

 milk fat solidifies, their slow solidification during standing 

 would cause an increase in density. 



The maximum density of milk is, unlike that of water, 

 coincident with its freezing point, about O55 C. or O3 C. 

 (Fleischmann). It expands w T hen heated at a rate which natu- 

 rally is dependent upon its composition, but is usually about 

 0002 for each degree Centigrade. 



According to Fleischmann" the coefficient of expansion of 

 milk increases with the temperature and with the proportion of 

 solid matter present. He found that the variations in volume 

 of ordinary milk (of specific gravity 1-0315 at 15) were as 

 follows : 



1,000,000 volumes at C. 

 become 1,000,030 ,, 1 C. 



1,000,391 4 C. 



1,001,273 10 C. 



1,002,134 15 C. 



1,003,800 20 C. 



1,006,414 30 C. 



1,014,277 50 C. 



1,019,243 60 C. 



When milk is heated the albuminoids apparently suffer 

 decomposition and sulphuretted hydrogen is evolved. 



The specific heat of milk is about 0-847. Its refractive 

 index (i.e., of the milk serum) is usually about 1-35. Skimmed 

 milk and whey show very similar numbers. 



Chemical Composition. Cows' milk varies considerably in 

 composition, its quality being dependent upon many circum- 

 stances, e.g., food, health, breed, age, &c., &c., of the animals. 



The mean composition is given by Bichmondf as 



% 

 Water ... ... 87'10 



Fat 3-90 



The Book of the Dairy, 1890, 13. t Dairy Chemistry, 120. 



