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. 
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 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 0.001 
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. 
