36 MILK 
water, the rinsings being collected in the beaker. 
The liquid is heated until all the copper is in 
solution, filtered, the filter washed until the 
filtrate amounts to at least 100 c.c., and elec- 
trolyzed. 
Electrolytic apparatus has been constructed 
in a great variety of forms. When the opera- 
tion is carried out frequently, it is best to have 
an electrolytic table. A platinum basin holding 
not less than 100 c.c. is used. A cylindrical form 
with flat bottom is convenient. It should rest 
on a bright copper plate, which is connected 
with the negative pole of the electrical supply. 
The positive pole should be also platinum, either 
a spiral wire, cylinder, or flat foil, Many 
operators use a funnel-shaped perforated ter- 
minal for the negative pole; in which case a glass 
beaker or casserole will be a suitable container, 
the positive terminal being placed within the 
negative. 
Four cells of a gravity battery will suffice 
for a single decomposition, and will operate 
two, but more slowly. It is usual to arrange 
the apparatus so that the operation may be 
continued during the night. When the elec- 
tricity is taken from the general supply of the 
laboratory, it is usually necessary to interpose 
resistance and to have some means of measuring 
the current-flow. This is sometimes done with 
