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 the heat is withdrawn, but the flow of hydrogen 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 



