88 MILK 



out taste or odor. Its specific gravity is 1.259. It does not melt 

 under the application of heat, and gives the protein reactions, ex- 

 cept Molisch and Adamkiewicz. One gram of casein furnishes 

 5742 calories. The valency of the protein molecule in basic case- 

 inates is 8; in basic paracaseinates, 4. The molecular weight is 

 given by different investigators from 6500 to 16,000; according to 

 Van Slyke and Bosworth it is 8888 for casein and 4444 for para- 

 casein. 



Bovine casein is soluble in weak alkahne solutions and these 

 solutions are levorotatory. When a small amount of alkaline 

 solution is mixed with casein a jelly of acid reaction is fornaed. 

 When more alkaline solution is added, an opalescent to milky 

 fluid results which filters through paper. More alkaline solution 

 renders the fluid clearer. 



Casein in alkaline solution does not pass through parchment 

 and is precipitated. Solutions in alkahes pass more readily 

 through porcelain filters than solutions in alkahne earths. Solu- 

 tions in alkaline earths are more milky than those in alkahes. 

 When solutions of casein are heated to temperatures above 40° C. 

 opalescence increases, and a film, known as haptogen membrane, 

 is formed which is similar to the film formed on heated milk. 

 This film is insoluble in water, but dissolves in alkalies. When 

 formed on milk it contains all the constituents of milk and may be 

 the result of evaporation. Casein is precipitated from solutions 

 by ammonium sulphate when the solutions are neutral or acid to 

 litmus. Alcohol precipitates casein in alkaline earth solutions, but 

 not in alkaline solutions. 



Casein is precipitated by dilute acids and redissolved in excess 

 of acid, forming acid caseins. When casein is shaken with dilute 

 acids a jelly is formed which dissolves when more acid is added. 

 From these solutions the casein is precipitated by alcohol, salts, 

 and neutralization of the acid, the amount of acid required for 

 casein precipitation varying according to the kind of acid and 

 the temperature. For example, it requires more acetic than 

 hydrochloric acid for precipitation, as shown by Hammarsten 

 and Raudnitz. The following figures give the amount of acid 

 required for complete precipitation of the casein in 1 liter contain- 

 ing 100 c.c. of milk and 900 c.c. of water: 



THE AMOUNT OF HYDROCHLORIC ACID AND ACETIC ACID REQUIRED FOE PRECIPITA- 

 TION OF CASEIN 



Kind of acid. 



N. 0.1 HCl 



N. 0.1 CHaCOOH 



In boiling milk the following amounts of acids are required for 

 coagulation according to Richmond : 



