52 METHODS OF ANALYSIS. 



before weighing; moisten previous to the filtration. Provide the tube with a 

 detachable funnel during the filtration, so that none of the precipitate accu- 

 mulates near the top, where it could be removed by the cork used during the 

 reduction of the cuprous oxid. Transfer all the precipitate to the filter and 

 thoroughly wash with hot w r ater, following the water by alcohol and ether 

 successively. After being dried, connect the tube with an apparatus for sup- 

 plying a continuous current of dry hydrogen, gently heat until the cuprous oxid 

 is completely reduced to the metallic state, cool in the current of hydrogen, and 

 weigh. If preferred, a gooch crucible may be used for the filtration. 



(2) ELECTROLYTIC DEPOSITION FROM SULPHURIC ACID SOLUTION. 



Filter the cuprous oxid in a gooch, wash the beaker and precipitate thoroughly 

 with hot water without any effort to transfer the precipitate to the filter. 

 Wash the asbestos film and the adhering cuprous oxid into the beaker by means 

 of hot dilute nitric acid. After the copper is all in solution, refilter through a 

 gooch with a thin film of asbestos and wash thoroughly with hot water. Ajdd 

 10 cc of dilute sulphuric acid, containing 200 cc of sulphuric acid (specific 

 gravity 1.84) per liter, and evaporate the filtrate on the steam bath until the 

 copper salt has largely crystallized. Heat carefully on a hot plate or over a 

 piece of asbestos board until the evolution of white fumes shows that the 

 excess of nitric acid is removed. Add from 8 to 10 drops of nitric acid 

 (specific gravity, 1.42) and rinse into a platinum dish of from 100 to 125 cc 

 capacity. Precipitate the copper by electrolysis. Wash thoroughly with water 

 before breaking the current, remove the dish from the circuit, wash with 

 alcohol and ether successively, dry at about 50 C., and weigh. If preferred, 

 the electrolysis can be conducted in a beaker, the copper being deposited upon 

 a weighed platinum cylinder. 



(3) ELECTROLYTIC DEPOSITION FROM SULPHURIC AND NITRIC ACID SOLUTION. 



Filter and wash as under (2). Transfer the asbestos film from the crucible 

 to the beaker by means of a glass rod and rinse the crucible with about 30 cc 

 of a boiling mixture of dilute sulphuric and nitric acids, containing 65 cc of 

 sulphuric acid (specific gravity, 1.84) and 50 cc of nitric acid (specific gravity, 

 1.42) per liter. Heat and agitate until solution is complete; filter and electro- 

 ]yze as under (2). 



(4) ELECTROLYTIC DEPOSITION FROM NITRIC ACID SOLUTION. 



Filter and wash as under (2). Transfer the asbestos film and adhering 

 oxid to the beaker. Dissolve the oxid still remaining in the crucible by means 

 of 2 cc of nitric acid (specific gravity, 1.42), adding it with a pipette and 

 receiving the solution in the beaker containing the asbestos film. Rinse the 

 crucible with a jet of water, allow the rinsings to flow into the beaker. Heat 

 the contents of the beaker until the copper is all in solution, filter, dilute the 

 filtrate to a volume of 100 cc or more, and electrolyze. When a nitrate solution 

 is electrolyzed, the first washing of the deposit should be made with water 

 acidulated with sulphuric acid, in order that the nitric acid may be all removed 

 before the current is interrupt <<!. 



(5) VOLUMETRIC PERMANGANATE METHOD. 



Filter and wash the cuprous oxid as described for method (2). Transfer the 

 asbestos film to the beaker, add about 30 cc of hot water, and heat the precipi- 

 tate and asbestos thoroughly. Rinse the crucible with 50 cc of a hot saturated 



