MILK 329 



8. Casein. Mix about 20 grams of milk with 40 c.c. of a saturated solution 

 of magnesuim sulphate and add the salt in substance until no more will dissolve. 

 The precipitate consists of casein admixed with a little fat and lacto-globulin. 

 Filter off the precipitate, wash it thoroughly with a saturated solution of magnesium 

 sulphate, 1 transfer the filter paper and precipitate to a Kjeldahl digestion flask, and 

 determine the nitrogen content according to the directions given in a previous 

 experiment (6). 



Calculation. Multiply the total nitrogen by the factor 6.37 to obtain the casein 

 content. 



9. Lactalbumin. To the nitrate and washings from the determination of 

 casein, in Experiment 8, add Almen's 2 reagent until no more precipitate forms. 

 Filter off the precipitate and determine the nitrogen content according to the direc- 

 tions given under Proteins, page 328. 



Calculation. Multiply the total nitrogen by the factor 6.37 to obtain the lactal- 

 bumin content. 



10. 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 pre- 

 cipitated proteins and the adherent fat with hot water. Combine the filtrate 

 and wash water and concentrate the mixture to about 150 c.c. Cool the solution 

 and dilute it to 200 c.c. in a volumetric flask. Titrate this sugar solution accord- 

 ing to directions given under Fehling's Method, page 523 or Benedict's Method, 

 page 522. 



Myers 3 recommends the following procedure for the determination of lactose 

 in milk. One part of milk is mixed with an equal volume of phosphotungstic 

 acid solution (70.0 grams acid and 200 c.c. cone. HC1 hi i liter of water) and 2-3 

 parts of water. Mix well, filter until clear, and titrate the clear filtrate against 

 Benedict's solution (25 c.c. reducing 67 mg. of lactose.) 



The milk may also be clarified for the lactose determination by means of 

 aluminum hydroxide 4 or dialyzed iron. 5 The dialyzed iron procedure is as follows* 

 Dilute 10 gm. of milk to 25 c.c. and add about 3 c.c. of 10 per cent colloidal iron 

 solution adding the last portion drop by drop to determine the exact amount 

 necessary. Filter and wash with water to make the clear filtrate 100 c.c. Titrate 

 using Benedict's method (see page 522). 



The preparation of aluminium hydroxide cream and its use in protein re- 

 moval are described under Nitrogen Partition, p. 485, Chapter XXVI. 



Calculation. Make the calculation according to directions given under 

 Fehling's Method, page 523, bearing in mind that 10 c.c. of Fehling's solution 

 is completely reduced by 0.0676 gram of lactose. 6 



1 Preserve the filtrate and washings for the determination of lactalbumin (Expt. 9). 



2 Almen's reagent may be prepared by dissolving 5 grams of tannic acid in 240 c.c. of 

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



3 Myers: Munch, med. Woch., 59, 1494, 1912. 



* Welker and Marsh: /. Am. Chem. Soc., 35, 823, 1913. 

 6 Hill: Jour. Biol. Chem., 20, 175, 1915. 



6 In case Benedict's method is used it should be remembered that 25 c.c. of the reagent 

 is reduced by 0.067 gram of lactose. 



