ANALYTIC PROCESSES 35 
small funnel is fitted tightly in the top of the tube. 
The object of this funnel is to prevent the pre- 
cipitate collecting on the upper part of the tube. 
The lower end of the funnel should project several 
centimeters below the bottom of the cork through 
which it passes. 
The filtering apparatus must be arranged 
prior to the precipitation, so that the cuprous 
oxid may be filtered without delay. The pre- 
cipitate is transferred as rapidly as possible to 
the filter, well washed with hot water, alcohol, 
and ether successively, dried, and the cuprous 
oxid reduced by gentle heating in a current of 
hydrogen. When the reduction is complete, 
the heat is withdrawn, but the flow of hydrogen 
is continued until the tube is cold. It is then 
detached and weighed. 
Reduction of Copper by Electrolysis —The fil- 
tration is performed in a Gooch crucible with 
an asbestos-felt film and the beaker in which the 
precipitation was made is well washed with 
hot water, the washings being passed through 
the filter, but it is not necessary to transfer 
all the precipitate. When the asbestos film is 
completely washed, it is transferred with the 
adhering oxid to the beaker; any oxid remaining 
in the crucible is washed into the beaker by use 
of 2 c.c. nitric acid (sp. gr. 1.42), added with a 
pipet. The crucible is rinsed with a spray of 
