ALBUMINOIDS. 309 



the form of a true emulsion, each globule being surrounded by 

 a layer of liquid, held in position by surface attraction. 



Rancidity. When butter fat becomes rancid the chief 

 changes are probably the hydrolysis of a portion of the fat into 

 free acids and glycerol, e.g.; C 3 H 5 (C 4 HA) 3 +3H 2 = C 3 H 5 (OH) 3 

 + 3HC 4 H 7 2 . The glycerol probably oxidises to acrolein, 

 C 3 H 4 0, or acrylic acid, C 8 H 4 2 . The fatty acids remain free, 

 and those which are volatile, e.g., butyric acid, give rise to the 

 odour of rancid butter. Oleic acid and other unsaturated acids 

 are oxidised, yielding substances some of which are soluble in 

 water, and which cause butter which has become rancid to 

 give a brown colouration when dissolved in warm alkali. 



Albuminoids. Much work has been done in connection 

 with the detection and separation of the proteids present in 

 milk, and very different views as to their number and nature 

 are held by various investigators. 



Duclaux affirms that casein is the only proteid present, but 

 that it exists in three forms casein in suspension, colloidal 

 casein, and casein in solution. The latter is found in the 

 nitrate when milk is passed through a porous earthenware cell, 

 while the other two are retained. The amount of the soluble 

 casein is about one-eighth of the total proteid. The colloidal 

 casein is that found in whey after the rennet has precipitated 

 the suspended casein. He quotes the following numbers" as 

 the results of an examination of milk and the whey formed 

 from it : 



In suspension. In solution. 



Milk. Whey Milk. Whey. 



Fat ... ... 4-30 0-85 



Sugar ... ... 5-37 5-73 



Casein ... ... 353 0-46 0-37 0-36 



Calcium phosphate... 0'23 O17 O17 



Salts 0-40 0-43 



8-06 1-31 6-31 6-69 



i 



Hammarsten (1872 1877) describes two albuminoids 



* Compt. Rend. 98, 438; Jour. Chem. Hoc., abst. 1884, 762. 



