MILK AND MILK PRODUCTS 27 



tannin, and the nitrogen in the precipitate determined as 

 above. 



The casein is found by subtracting the figure for albumin 

 from that for total proteids. 



Lactose. — For this determination, A. O. A. C. employs 

 Soxhlet 's method with the following reagents : 



Copper sulfate solution. — 34.639 grams of pure crystallized 

 copper sulfate are dissolved in water and made up to 500 c.c. 



Alkaline tartrate solution. — 173 grams of pure sodium potas- 

 sium tartrate and 50 grams of good sodium hydroxid are dis- 

 solved in water and the solution made up to 500 c.c. 



Half-normal sodium hydroxid. 



25 c.c. of the sample in a 500 c.c. flask are diluted with 400 

 c.c. of water and 10 c.c. of the copper sulfate solution and 8.8 

 c.c. ^- sodium hydroxid solution added. The mixture should 

 still have an acid reaction and contain copper in solution. If 

 this is not the case, the experiment must be repeated, using a 

 little less of the alkali. The flask is filled to the mark with 

 water, shaken, and the liquid passed through a dry filter. 50 

 c.c. of Fehling's solution, obtained by mixing equal parts of 

 the above copper sulfate and alkaline tartrate solutions, are 

 heated to brisk boiling in a 300 c.c. beaker, 100 c.c. of the 

 filtrate obtained as above added, and boiling continued for six 

 minutes; the liquid then promptly filtered, and treated accord- 

 ing to methods given below. The amount of lactose is calculated 

 by the table on page 28 from the copper obtained by table. 

 The figures for weights of copper between any two data given 

 in the table may be calculated with sufficient accuracy for 

 practical purposes by allowing 0.0008 gram of lactose for each 

 o.ooi gram of copper. 



The precipitated cuprous oxid is usually converted into free 

 copper and weighed as such. Two methods may be employed 

 for reduction: by hydrogen or by electrolysis. 



