34 ANALYTICAL PROCESSES. 



mixed, the volume noted, and allowed to stand 

 until the separation takes place. The liquid is then 

 filtered, as much as possible of the clear portion being 

 drawn off with a pipette, and passed through the 

 filter. An aliquot portion of the filtrate is taken, 

 the albumin precipitated by a solution of tannin, and 

 the nitrogen in the precipitate determined as above. 



The casein is found by subtracting the figure for albu- 

 min from that for total proteids. 



The Ritthausen Method for Total Proteids.— 



This method depends on the precipitation of the 

 albuminoids by means of copper sulfate and sodium 

 hydroxid. It is applicable only to fully developed 

 milks ; the proteids of colostrum are only partially pre- 

 cipitated. The following reagents are required. 



Copper Sulfate Solution. — 34.64 grams of pure crys- 

 talized' copper sulfate are dissolved and made up to 

 500 c. c. 



Sodium Hydroxid Solution. — About 1 2 grams are dis- 

 solved in 500 c. c. of water. 



10 grams of the milk are placed in a beaker, diluted 

 with lOp c. c. of distilled water, 5 c. c. of copper sul- 

 fate solution added and thoroughly mixed. The, 

 sodium hydroxid solution is then added drop by drop 

 with constant stirring, until the precipitate settles 

 quickly and the liquid is neutral,' or at most very feebly 

 acid. An excess of alkali will prevent the precipita- 

 tion of some of the proteids. 



