qf Electro-precipitated Metals, - 19 



of crystallization in electro-metallic deposits. The drawing is 

 made 200 times the natural size. 



To return to an electro-copy of a wood engraving: it is found 

 by examination under the microscope, and would be antici- 

 pated from the preceding remarks, that each line has a space 

 in its centre ; they are in fact exceedingly hollow, and present 

 much the appearance of the hollow crystallized cakes of sugar 

 made by confectioners, and hence we see the advantage of 

 thoroughly tinning it at the back as soon as we have removed 

 the cast from its matrix; the tin insinuates itself into a great 

 number of the pores and binds the whole firmly together. 

 With the help of a little chloride of zinc the tinning is effecced 

 very readily, and should be done without disturbing the struc- 

 ture by filing. 



There is one phaenomenon, connected with the employment 

 of electro-casts, exceedingly curious — it is their uselessness 

 for printing with vermilion ink (sulphuret of mercury), which 

 is not the case with respect to ordinary engraved copper 

 blocks. When an electro-cast is inked over with vermilion 

 printing ink, and a few impressions have been taken, the 

 vermilion is blackened, and as the process is continued the 

 copper begins to get white, and at last so much mercury is 

 precipitated on the surface as to prevent the adherence of 

 the ink. 1 am inclined to think that the porous and divided 

 nature of the electro-cast is the sole cause of its decomposing 

 the vermilion, and that the purity of the copper is not con- 

 cerned in it. 



In most of the preceding remarks I have alluded to depo- 

 sits of copper, but I wish it to be understood that they apply 

 equally to gold, silver or other metals ; and such being the 

 nature of precipitated metals, 1 consider that though the 

 electro-melallurgic processes are a valuable addition to the 

 arts, there are uses to which they should not be applied ; as, 

 for example, the coating of one metal with another when it is 

 intended to protect the covered metal from the action of cer- 

 tain fluids, at all events wihout the precaution in all possible 

 cases of subsequently partially fusing the coating metal. 



The production of ornamental pieces of plate, and the sil- 

 vering or gilding of such objects as are not subject to much 

 friction, is not open to the same objections. Platinum and 

 palladium also, if ever obtained by the electro-metallurgic 

 process in plates or other forms, should subsequently be sub- 

 jected to the process of welding and hammering. It has been 

 proposed to copper the bottoms of ships by this process ; apart 

 from the great difficulty of effecting this on a large scale, the 

 copper in my opinion would be far too friable for such a use, 



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