142 MILK. 



in a nickel dish or crucible. Dissolve the residue in water and test 

 for phosphoric acid with magnesia mixture; or test for the same 

 substance after acidifying by nitric acid with ammonium molyb- 

 date. Mix another portion of the dry protagon in a glass tube 

 with soda-lime, hold horizontally by a clamp and heat. Show that 

 it contains nitrogen from the evolution of ammonia as is demon- 

 strated by the action of the gas on red litmus paper. 



322. Pulp another brain and warm it with barium hydrate 

 solution (saponification). Filter. The mass on the filter contains 

 cerebrin, cholesterin, barium soap, and connective tissue. Heat 

 this with alcohol and filter while hot, thus dissolving out the 

 cholesterin and cerebrin. When the liquid cools they separate and 

 are recognizable by their crystalline forms. The cholesterin is in 

 flat thin plates, the cerebrin in clusters of needle-shaped crystals. 



Extract the cholesterin by ether, and recrystallize. Test a 

 part of the cerebrin by heating with soda-lime for nitrogen as in 

 Experiment 72. Boil a part for an hour with dilute sulphuric acid 

 to hydrolize it; then show its reducing power with Trommer's 

 reagent. Observe that before hydrolysis it does not reduce. 



MILK. 



The solids of milk are partly dissolved and partly in 

 suspension in the liquid. Of the dissolved -constituents the 

 most important are milk-sugar, an albumin, a globulin, and 

 some mineral salts. Among the suspended compounds 

 are casein, fat, and calcium phosphate. The average 

 amount of solids in normal cows' or human milk is 12 or 

 13 per cent, by weight. The reaction of fresh cows' or 

 human milk is nearly neutral, or may be amphoteric to 

 litmus; that is, it turns red paper blue and blue paper red. 



The specific gravity should be between 1.029 and 

 1.033 at 15, and of milk which has been skimmed after 

 standing twenty-four hours it should be between 1.0325 

 and 1.0365. Thus the removal of fat raises the specific 



