ANALYTIC PROCESSES 33 



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. 

 SO 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 according to methods given below. 

 The amount of lactose is calculated by the table 

 on page 34 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 con- 

 verted into free copper and weighed as such. 

 Two methods may be employed for reduction: 

 by hydrogen or by electrolysis. 



Reduction by Hydrogen. — The curpous oxid is 

 collected on an asbestos filter. This is arranged 

 most conveniently in a special filtering tube, 

 which is shown in figure 2. The wider part is 

 about 8 cm. and 1.5' cm. in diameter, the narrower 

 portion about 5 cm. long and 0.5 cm. in caliber. 



