692 GALVANO-PLASTICS. 



cupric sulphate into which a copper plate dips which is connected 

 with the positive pole and forms the anode. 



The process may be still further simplified if the deposition of 

 copper which takes place in a galvanic cell containing cupric sul- 

 phate is used directly for the production of the galvano-plastic copy. 

 Graphite behaves nearly like copper in a galvanic cell, and the 

 stearine cast covered with black-lead may therefore be at once sub- 

 stituted for the copper in a cell of the form shown in fig. 348 C. 



The perpendicular portion of the wire attached to the stearine 

 cast should be varnished with ' black japan ' before putting it into 

 the cell, this will prevent the deposition of copper upon it ; the 

 upper extremity is clamped to the connecting wire of the zinc 

 cylinder by a binding screw. The magnesic sulphate solution 

 should for this experiment be much weaker than that previously 

 used, so as to possess less conductivity, for the current must be very 

 feeble ; as much of the solid salt as can be taken up with the point 

 of a knife is quite sufficient for the whole cell. The crystals of the 

 cupric sulphate must in this case not be thrown into the vessel but 

 cautiously placed all round the stearine cast, using the crucible 

 tongs for the operation. The dark blue solution must stand at 

 least a few millimetres above the stearine. After from three to 

 eight days, during which time the used crystals must be replaced 

 now and then by others, the deposit will be thick enough to be 

 taken off. Any bits of copper deposited round the lower surface 

 of the stearine are first cautiously broken away, and the copper 

 deposit on the upper surface is then raised ; if this cannot be done 

 the stearine is melted off. In order to give the copy a neat appear- 

 ance the adhering edge must be removed. For this purpose the 

 inner side or reverse of the copy is moistened with soldering liquid, 

 a little solder placed upon it, and heated until it flows and spreads 

 over the whole surface. The copper deposited by the current is 

 very brittle, and even when very thick and substantial in appearance 

 the file cannot be applied to it for removing the edge, but the 

 back of solder will render it firm enough for using the file for the 

 purpose. 



Casts often have small holes, and if there are any the melted solder 

 would clearly run through them and spoil the whole. These holes 

 are caused by air bubbles which adhere to the surface of the stearine 

 when the latter is introduced into the cell. It is therefore advisable 

 to remove at once all visible bubbles with a pointed camel' s-hair 

 brush, taking care, however, not to brush too hard along the sur- 

 face, otherwise portions of the thin conducting layer might be re- 

 moved altogether. 



