Cojjper hy Voltaic Electricity. 313 



heating it and allowing it to cool slowly it becomes tough and 

 flexible. 



In this process it is evident that a metallic surface is re- 

 quisite for the commencement of any precipitation of copper; 

 the arrangement in fact forms a single ceil of a Daniell's bat- 

 tery, and is incomplete with the presence of the surface of the 

 second metal in the sulphate of copper. 



Mr. Spencer has shown, however, that moulds for the pre- 

 cipitation of copper may be made of any substance by gild- 

 ing them or otherwise coverino; their surface with a thin film 

 of metal which affords a conducting surface for the first por- 

 tions of copper to be precipitated upon. My attention was 

 early directed to this part of the process, because it seemed to 

 open a wide field for new and beautiful applications. I was 

 induced to pay particular attention to the deposition of copper 

 upon non-metallic surfaces, and in consequence made nu- 

 merous experiments to ascertain the circumstances most fa- 

 vourable to its precipitation under these conditions. My first 

 experiments were made on surfaces of plaster of Paris, 

 which I endeavoured to coat with copper, so as in fact to con- 

 vert plaster casts into bronzes. I commenced by gilding the 

 surface with different metals in the manner proposed by Mr. 

 Spencer, but I found it exceedingly difficult to get a perfectly 

 smooth and uniform surface ; the process succeeded best with 

 gold-leafj but even that had its objections, and was besides 

 very expensive. Subsequently I tried metals, such as bismuth 

 and antimony in a state of very fine division, ground up with 

 water and glutinous matters ; these attempts were however 

 not much better than the first trials. 



In the course of these experiments I observed a curious 

 fact, which I had not at all anticipated, and which ver}' ma- 

 terially assisted me in attaining the objects which I had in 

 view. When I had endeavoured to precipitate lead from a 

 solution of one of its salts, in the same way that I had been 

 doing with copper, I found that small grey crystals of lead 

 soon formed upon the most prominent parts of the metallic 

 mould I was employing, and which happened to be a leaden 

 cast of a medal : these crystals rapidly increased in size, extend- 

 ing towards the membrane bag containing the zinc, which was 

 about 3 inches distant from the mould. As soon as the cry- 

 stals reached the surface of the membrane they bent about 

 in various directions, crossing and recrossing each other until 

 they had completely enveloped the membrane in a net-work 

 of reduced lead. Again, when silver is precipitated from the 

 fused nitrate, by electricity, the crystals formed at the one 

 electrode extend across the fused electrolyte, until having 



