PHYSICAL AND CHEMICAL EXAMINATION OF MILK 183 



oven, dried at 130 C., and weighed. The precipitate with filter 

 are incinerated in a porcelain crucible and the weight of the residue 

 deducted from the first weight. The result gives the weight of the 

 protein. 



Determination of Casein and Albumin. Method of the As- 

 sociation of Official Agricultural Chemists: "The milk should be 

 kept fresh, or if this is not possible, 1 part formaldehyd is added 

 to 2500 parts milk and the milk kept on ice. About 10 grams of 

 the milk are placed in a beaker with about 90 c.c. of water at 40 to 

 42 C. k and 1.5 c.c. of a. 10 per cent, acetic acid solution added. 

 The mixture is stirred with a glass rod and allowed to stand for 

 three to five minutes or longer. The supernatant fluid is decanted 

 on a filter, the precipitate washed with cold water two or three 

 times by decantation, and the precipitate transferred completely 

 to the filter. The precipitate is then washed once or twice on the 

 filter. The filtrate should be clear or nearly so. If it does not 

 run clear, the filtrate is poured back and this process repeated two 

 or three times, after which the washing of the precipitate can be 

 completed. The nitrogen is determined in the washed precipitate 

 by the Gunning method. The nitrogen is multiplied by 6.38 to 

 obtain the amount of casein. 



"The filtrate obtained is neutralized exactly with alkali and 0.3 

 c.c. of a 10 per cent, acetic acid added. The liquid is heated to the 

 boiling temperature until the albumin is completely precipitated. 

 The precipitate is collected on a filter, washed, and the nitrogen 

 determined by the Gunning method. The result is multiplied by 

 6.38. 



11 Optional Method of Determining Casein and Albumin. To 

 10 c.c. of milk 50 c.c. of distilled water at 40 C. are added, and 

 then 2 c.c. of alum solution saturated at 40 C. or higher. The 

 precipitate is allowed to settle, transferred to a filter, and washed. 

 Nitrogen is determined by the Gunning method. 



"To the filtrate 0.3 c.c. of a 10 per cent, acetic acid solu- 

 tion are added and the mixture boiled until the albumin has 

 been completely precipitated and the nitrogen determined as 

 before. 



"Leffman and Beam's Method for Determining Casein and 

 Albumin. Twenty c.c. of milk are mixed with saturated solution 

 of magnesium sulphate and the mixture saturated with the pow-. 

 dered salt. The whole is then washed into a graduate with a little 

 saturated solution and the precipitate allowed to settle. The 

 volume of the mixture in the graduate is noted and as much as 

 possible of the clear supernatant fluid removed with a pipet and 

 filtered. 



"An aliquot portion of the filtrate is taken and the albumin 



