XV. 



MILK AND MILK PEODUCTS 



321 



causes, but that that of the dissolved matters obeys the general rule of 

 the freezing of solutions ; viz., the frozen solid portion is poorer in- 

 dissolved matter than that remaining liquid. 



According to Fleischmann 1 the co-efficient of expansion of milk in- 

 creases 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 : 



become 



1,000,000 volumes at C. 

 1,000,030 1 C. 



1,000,391 4 C. 



1,001,273 10 C. 



1,002,134 

 1,003,800 

 1,006,414 

 1,014,277 

 1,019,243 



15 C. 

 20 C. 

 30 C. 

 50 C. 

 60 C. 



When milk is heated, the albuminoids apparently suffer decompo- 

 sition 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 circumstances, 

 e.g., food, health, breed and age of the animals. 



The mean composition is given by Eichmond 2 as 



Water . 

 Fat . 

 Milk sugar 

 Casein 

 Albumin 

 Ash 

 Citric acid 



Per cent. 

 87-10 

 3-90 

 4-75 

 3-00 

 0-40 

 0-75 

 0-10 



Colostrum. The first milk after calving is known as colostrum, or 

 " beestings," and is essentially different from normal milk. 



It is a yellow liquid, with strong pungent taste, containing large 

 numbers of small clusters or cells " colostrum granules " which 

 vary in diameter from *005 to *025 millimetres and apparently result 

 from the breaking up of the milk glands. 



Eugling 3 gives the composition of the colostrum of 22 cows as 

 varying between 



Fat . 



Casein 

 Albumin 

 Sugar . 

 Ash . 

 Total solids 

 Specific gravity 



1-88 

 2-64 



11-18 

 1-34 

 1-18 



24-34 

 1-059 



to 



4-68 

 7-14 



20-21 

 3-83 

 2-31 



32-57 

 1-079 



The fat of colostrum has a higher melting-point (40-4:6 ) and 



1 The Book of the Dairy, 189S, 13. 2 Dairy Chemistry, 120. 



3 Jour. Chem. Soc., 1879, Abstracts, 815 ; also Ladenburg's Handworterbuch 

 der Chemie. 



21 



