CASEIN. 229 



phosphate, and this multiplied by 51 -3 will give an estimate of 

 the casein. 



Solubility. To 1 gramme in a test-tube add 15 c.c. of water, 

 shake well, warm to 50 C., and shake again. A soluble casein 

 should dissolve. 



If not, add 0-125 gramme of sodium carbonate to 5 grammes, 

 mix well, and then test solubility,, a good casein should now 

 dissolve. 



Samples should be ground to a fine powder before being tested 

 for solubility. The following determinations may be made 

 on the filtrate obtained by adding acid mercuric nitrate (4 c.c. 

 to 100 c.c.) to a 5 per cent, solution ; calcium, magnesium, potash, 

 soda, chlorides, sulphates, phosphates, citrates, acetates, and 

 nitrogen in phospho-tungstic acid precipitate. These deter- 

 minations will give a clue as to the mode of preparation of the 

 casein. 



Baier and Neumann estimate casein in solid preparations, 

 and especially in milk chocolate, as follows : 



Ten grammes of the fat free substance are rubbed up in a 

 mortar with a 1 per cent, sodium oxalate solution, and the paste 

 washed into a 250 c.c. flask with about 200 c.c. of the sodium 

 oxalate, the solution heated to boiling, and made up approxi- 

 mately to volume with hot oxalate solution. After standing 

 for eighteen to twenty-four hours, being shaken at intervals, 

 the solution is made up to volume, and 100 c.c. of the mixed 

 filtrate is treated with 5 c.c. of 5 per cent, uranium acetate 

 solution, and 33 per cent, acetic acid added, drop by drop, till 

 the casein separates ; the precipitate is centrifuged or filtered, 

 washed with water containing 5 per cent, of uranium acetate 

 solution and 3 per cent, of acetic acid solution per 100 c.c., and 

 the nitrogen estimated by the Kjeldahl method, and the result 

 multiplied by 6-39. 



The following formulae will give approximations to the amount 

 of milk constituents calculated from the casein present in prepar- 

 ations such as milk chocolate. 



Casein X 1-14 = Total proteins 



X 1-56 = Milk-sugar ! . . ,., 

 X 0-25 - Ash f of milk sollds ' 



X 2-95 = Solids not fat J 



