54 



should be clotted. Leave this tube in the water bath if neces- 

 sary, until the whey has separated quite completely from the 

 curd. Filter and use the filtrate in the following tests. 



191. Test one portion of the whey filtrate by adding a 

 few drops of nitric acid and a little ammonium molybdate 

 solution and heat. A yellow precipitate indicates phospates. 

 Test another portion by adding a little silver nitrate. A 

 white precipitate insoluble in nitric acid indicates chlorides 

 (chiefly potassium and sodium). To another portion add a 

 little ammonium oxalate. A precipitate indicates calcium 

 salts. Test the remaining portion for albumin using the 

 xanthoproteic test. 



192. To a test tube half full of milk add 3 or 4 drops of 

 a saturated solution of ammonium oxalate ; mix, add a tablet 

 of rennin and digest at 38°-40°C. for at least a half an hour. 

 There should be no coagulum. Then add a few drops of a 2% 

 solution of calcium chloride and digest again. Does the milk 

 coagulate ? 



193. Separation of caseinogen by salts. To a test tube 

 half full of milk, add crystals of magnesium sulphate or 

 sodium chloride to saturation. The caseinogen and fat separate 

 out, rise to the surface, and leave a clear salted whey beneath. 

 Caseinogen, like globulins, is precipitated by saturation with 

 MgSOj or NaCl, but it is not coagulated by heat. It was at 

 one time supposed to be an alkali albumin, but the latter is 

 not coagulated by rennin. It appears to be a nucleo-albumin 

 — i. e., a compound of a proteid with nuclein, the latter a body 

 rich in phosphorus. 



194. Boil a little milk in a small beaker or evaporating 

 dish. There is no coagulation. A scum forms upon the sur- 

 face which returns as often as it is removed. This is due 

 chiefly to caseinogen entangled in protein drying on exposure 

 to air. 



195. Place a small quantity of milk in a warm place for 

 one or two days ; then test the reaction, it will be found to be 

 acid ; this is due to fermentation, in the process of which the 

 milk sugar is converted into lactic acid. 



