MILK ASH. 315 



extremes of seven analyses of the mixed milk of 10 cows taken 

 at various times of the year : 



o/ o/ 



Potash... ... ... 22-56 to 26-94 



Soda ... ... ... 10-26 to 11-97 



Lime ... ... ... 19-71 to 23-57 



Magnesia ... ... 1-78 to 3-15 



Ferric oxide ... ... traces to 0'21 



Sulphur trioxide ... ... 3*75 to 4-38 



Phosphorus pentoxide ... 22-41 to 26-51 



Chlorine ... ... 13-15 to 16-15 



Of the ash about one-third is usually soluble in water and 

 consists mainly of alkaline chlorides and carbonates. Much 

 of the basic material of the ash exists in the milk in associa- 

 tion with the casein and in union with citric acid. 



Citric acid is present in milk to the extent of about 0*1%* 

 and crystals of calcium citrate are sometimes found in con- 

 densed milk. The presence of the citric acid probably accounts 

 for a portion of the calcium phosphate of milk being in solu- 

 tion. 



The gases contained in milk are chiefly carbon dioxide, 

 oxygen, and nitrogen. From a litre of milk Pfliiger (1869) 

 obtained 1 c.c. oxygen, 76 c.c. carbon dioxide, 7 c.c. nitrogen. 



Cows' Milk. Cows' milk, being the most important from a 

 commercial and agricultural standpoint, has been studied much 

 more thoroughly than the milk of other animals. 



Cows' milk is a white, or yellowish white, opaque liquid of 

 sweet taste. Its specific gravity varies usually between 1-027 

 and 1-034, but in certain cases may be outside these limits. 



When freshly drawn and quickly cooled, milk has a certain 

 specific gravity, but shows a decided increase in density (about 

 0005) on keeping at the same temperature for some hours. 

 This phenomenon, known as Eecknagel's phenomenon,! has 

 been attributed to a molecular change in the casein and to the 

 presence of air bubbles, which gradually escape ; but is more 

 likely to be due, as suggested by Kichmond, to the fact that 



* Henkel & Soxhlet, Jour Chem. Hoc. 1889, abst. 178. t Berichte 14, 2684 



