MILK 347 



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 541, or Benedict's Method, 

 page 538. 



Myers 1 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 in 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. reduced by 67 mg. of lactose). 



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

 aluminum nydroxide 2 or dialyzed iron. 3 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 col- 

 loidal 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 538). 



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

 moval are described under Nitrogen Partition, p. 506, Chapter XXVII. 



Calculation. Make the calculation according to directions given under 

 Fehling's Method, page 541, bearing in mind that 100 c.c. of Fehling's solution 

 is completely reduced by 0.0676 gram of lactose. 4 



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

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

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



4 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. 



