412 PHYSIOLOGICAL CHEMISTRY. 



5. Proteins. Introduce a known weight of milk (5-10 grams) 

 into a 500 c.c. Kjeldahl digestion flask and add 20 c.c. of con- 

 centrated sulphuric acid and about 0.2 gram of cupric sulphate. 

 Expel the major portion of the water by heating over a low flame 

 and finally use a full flame and allow the mixture to boil 1-2 hours. 

 Complete the determination according to the directions given under 

 Kjeldahl Method, page 381. 



Calculation Multiply the total nitrogen content by the factor 

 6.37 1 to obtain the protein content of the milk examined. 



6. Caseinogen. Mix about 20 grams of milk with 40 c.c. of a 

 saturated solution of magnesium sulphate and add the salt in sub- 

 stance until no more will dissolve. The precipitate consists of 

 caseinogen admixed with a little fat and lacto-globulin. Filter off 

 the precipitate, wash it thoroughly with a saturated solution of 

 magnesium sulphate, 2 transfer the filter paper and precipitate to 

 a Kjeldahl digestion flask and determine the nitrogen content ac- 

 cording to the directions given in the previous experiment. 



Calculation. Multiply the total nitrogen by the factor 6.37 to 

 obtain the casein content. 



7. Lactalbumin. To the filtrate and washings from the deter- 

 mination of caseinogen, as just explained, add Almen's reagent 3 

 until no more precipitate forms. Filter off the precipitate and 

 determine the nitrogen content according to the directions given 

 under Proteins, above. 



Calculation. Multiply the total nitrogen by the factor 6.37 to ob- 

 tain the lactalbumin content. 



8. Lactose. To about 350 c.c. of water in a beaker add 20 

 grams of milk, mix thoroughly, acidify the fluid with about 2 c.c. 

 of 10 per cent acetic acid and stir the acidified mixture continuously 

 until a flocculent precipitate forms. At this point the reaction 

 should be distinctly acid to litmus. Heat the solution to boiling 

 for one-half hour, filter, rinse the beaker thoroughly and wash the 

 precipitated proteins .and the adherent fat with hot water. Com- 

 bine the filtrate and wash water and concentrate the mixture to about 



1 The usual factor employed for the calculation of protein from the nitrogen 

 content is 6.25 and is based on the assumption that proteins contain on the 

 average 16 per cent of nitrogen. This special factor of 6.37 is used here to 

 calculate the protein content from the total nitrogen, since the principal protein 

 constituents of milk, i. e., caseinogen and lactalbumin, contain 15.7 per cent 

 of nitrogen. 



2 Preserve the filtrate and washings for the determination of lactalbumin. 



3 Almen's reagent may be prepared by dissolving 5 grams of tannin in 240 c.c. 

 of 50 per cent alcohol and adding 10 c.c. of 25 per cent acetic acid. 



