14 HANDBOOK FOR BIO-CHEMICAL LABORATORY. 



with only a slight bluish opalescence. After diluting with 

 water it is again precipitated by acetic acid (or hydrochloric 

 acid) as above directed, and the precipitate again ground 

 finely, washed on a filter with water, and then dissolved in caus- 

 tic soda as above. This is repeated once or twice. Then the 

 washed precipitate is gently pressed, quickly rubbed to a 

 paste with 97$ alcohol, transferred to a filter, washed first 

 with alcohol, then with ether, pressed, then dried in a mortar 

 after having finely divided it. The last traces of ether are 

 removed in a vacuum or over sulphuric acid. (Hammarsten.) 

 Properties. Casein forms a white, dusty, insoluble powder 

 which reddens moist blue litmus-paper. It is readily soluble 

 in dilute alkalies and acids. It is completely soluble in 0.2$ 

 hydrochloric acid, and if this is digested at 38-40 0. with 

 pepsin a gradual cloudiness is formed and a precipitate of 

 nuclein is produced. Casein solutions do not coagulate on 

 boiling, but are covered, as milk, with a skin. Casein is pre- 

 cipitated from neutral solutions or from milk by NaCl or 

 MgS0 4 in substance without changing its properties. Metallic 

 salts, such as copper sulphate, completely precipitate casein 

 from neutral solutions. Casein coagulates with rennet or 

 chymosin in the presence of lime-salts. 



Albuminate (Alkali). 



Preparation. Beat up the white of an egg finely and filter 

 through a piece of clean linen, and treat the filtrate with 

 a solution of 1 grm. caustic potash in a little water, contin- 

 ually stirring. The solution will be immediately, or after 

 some time, converted into a gelatinous mass. This is cut into 

 pieces, washed a few times with water, then dissolved in warm 

 water, allowed to cool, and precipitated by acetic acid, wash- 

 ing the precipitate with alcohol and ether. This precipitate 

 of alkali albuminate appears as a flaky, amorphous, white 

 substance, nearly insoluble in water as well as NaCl solutions, 



