PRINTING. 79 



made water-tight. Into one division of the vat was placed the 

 dilute acid and sheets of zinc; in the other the solution of copper, in 

 which was placed the cloth upon the frame. The arrangement was 

 so perfect that we have often seen pieces of cloth, twelve yards 

 long by one yard wide, completely covered with copper in one 

 hour. The result of many trials was, that one pound weight of 

 copper gave a perfect solid covering to twenty superficial square 

 feet of cloth. 



A similar thickness is quite sufficient for other surfaces not 

 affected by the atmosphere, such as wood, &c. &c. 



Besides these applications, a host of others have been suggested 

 and tried with variable success. Some have probably been aban- 

 doned too soon, others have had both capital and talent applied, 

 and success is yet to come. We shall only name a few of these 

 applications. 



Calico-Printers' Rollers. So early as 1841 active means were 

 tried to apply the electro-deposition of copper to the preparation of 

 rollers for printing calicoes, both by depositing the copper upon wax 

 or other moulds, to make an entire roller of copper, or to deposit a 

 surface of copper on other metals, such as iron or brass ; but none 

 of them have yet succeeded. To make an entire roller is much more 

 expensive, without an equivalent advantage over the ordinary me- 

 thod of casting, rolling, and boring. To deposit a layer of copper 

 on iron is attended with many practical difficulties, both in protect- 

 ing the iron from the acid solution for so long a time as is required 

 to deposit the proper thickness, and in securing the adhesion of the 

 two metals during the subsequent operations. It requires a deposit 

 of about a quarter of an inch in thickness to allow for turning before 

 engraving. There is then the annealing to soften the copper, &c., 

 which interferes with the adhesion of the two metals, probably 

 from their different rates of expansion, and other causes. Similar 

 objections may be made to the coating of brass rollers with copper. 

 Numerous and varied have been the experiments made, but all 

 without success. 



Etching of Rollers. The last application of the process to printers' 

 rollers was to plate the surface of the roller with silver for the pur- 

 pose of etching. The engraving is then made through the silver 

 coating; the roller is next passed through nitric acid, which acts 

 upon the exposed copper, the silver taking the place of varnish in 

 ordinary etching : but practical difficulties have caused the abandon- 

 ment of this method also ; so that, so far as we are aware, no really 

 practical and useful application of the electrotype process has yet 

 been made to printers' rollers. 



Printing. The electro-metallurgical process has been applied to 

 many operations in ordinary printing. Mr. WARREN DE LA RUE 



