26 MILK 



gram of zinc dust is added. 50 c.c. of the strong 

 sodium hydroxid solution, or suflEicient to make 

 the reaction strongly alkaline, should be slowly 

 poured down the side of the flask so as not to mix 

 at once with the acid solution. It is convenient 

 to add to the acid liquid a few drops of phenol- 

 phthalein or azolitmin solution, to indicate when 

 the liquid is alkaline, but it must be noted that 

 strong alkaline solutions destroy the former 

 indicator. The flask is shaken so as to mix the 

 alkaline and acid liquids and at once attached to 

 the condensing apparatus. The receiving fiask 

 should have been previously charged with a 

 carefully measured volume of the ^/^ acid (10 c.c. 

 diluted with distilled water to 100 c.c. is a 

 convenient amount). The distillation is con- 

 ducted until about 150 c.c. have passed over. 

 A smaU amount of indicator is added, the liquid, 

 titrated with standard alkali, and the amount 

 neutralized by the distilled ammonium hydroxid 

 determined by subtraction. Each c.c. of ^/^ 

 acid neutralized is equivalent to 0.007 nitrogen. 

 The nitrogen multiplied by 6.38 gives the 

 total proteins. 



The distillation in this operation requires 

 care, as the amount of ammonium hydroxid is 

 determined by its neutralizing power, hence 

 solution of the alkali of the glass will introduce 

 error. Common glass is not satisfactory. Block 



