THE MILK. 411 



I. u. 



Potassium (K 2 O) ................ 0.780 0.703 



Sodium (Na, 2 0) ................ 0.232 0.257 



Calcium (CaO) ................. 0.328 0.343 



Magnesium (MgO) ............... 0.064 0.065 



Iron (Fe 2 3 ) .................. 0.004 0.006 



Phosphoric acid (P 2 O 5 ) ............. - 473 - 4ti9 



Chlorine (Cl) .................. 0.438 0.445 



The differences which exist in the composition of full milk, as 



compared with skimmed milk, cream, buttermilk, and whey, are 

 shown below : 



Cream ' Buttermilk. Whey. 



Water . . 871.7 906.6 655.1 902.7 932.4 



Solids ...... 128.3 93.4 344.9 97.3 67.6 



Albumins . . 35.5 31.1 35.5 35.5 8.5 



Fats .... 36.9 7.4 267.5 9.3 2.3 



Lactose , . . 48.8 47.5 35.2 37.3 47.0 



Lactic acid . . none none none 3.4 3.3 



Salts ..... 7.4 7.4 6.1 6.7 6.5 



Of gases, milk contains a small amount of oxygen and nitrogen, 

 and from 5.8 to 7.5 per cent, of carbon dioxide, which can be 

 removed with the exhaust pump. 



The Albumins. The albumins which are found in milk are casein, 

 lactalbumin, and so-called lactoglobulin, which is probably identical 

 with the serum-globulin of the blood-plasma. Of these, casein is 

 the most abundant and the most important. 



CASEIN. Casein is a nucleo-albumin, and has the character of 

 a dibasic acid. In the dry state it occurs as a white amorphous 

 powder, which is almost insoluble in water, in dilute acids, and solu- 

 tions of the neutral salts. In dilute solutions of the alkaline hydrates 

 and in lime-water it dissolves with ease, at the same time forming 

 salts. Such solutions are neutral or slightly acid in reaction, accord- 

 ing to the amount of alkali that has been added, which is owing to the 

 formation of neutral or acid salts, respectively. When triturated in 

 water with calcium or sodium carbonate, the carbonates are decom- 

 posed with the liberation of carbon dioxide ; the same salts are then 

 formed as in the case of the alkaline hydrates. Soldner has isolated 

 two calcium salts of casein, containing 1.55 and 2.36 per cent, of 

 calcium oxide; according to Courant, these are dicalcium and 

 tricalcium casei'n, respectively. The salts of casein with the alkalies 

 and alkaline earths are readily soluble in water, even in the absence 

 of neutral salts, and are hence not precipitated on dialysis. On 

 decomposition with dilute acids the free casein is obtained again in 

 insoluble form. Suspended in water, the substance is coagulated on 

 boiling, and can then no longer be dissolved without undergoing 

 denaturization, as on boiling with acids and alkalies. Solutions of 

 the casein salts, on the other hand, do not coagulate on boiling, but 

 form a surface skin, as in the case of milk. The salts can be pre- 

 cipitated from their solutions by salting with sodium chloride or 



