EledrograpJiy. 163 



The wood-engraver can now furnish blocks which will admit 

 of much greater delicacy of finish, although it is doubtful if any 

 material can endure the common press for a longer time than well 

 prepared wood is stated to have done. But the ease and accuracy 

 with which the most elaborate designs may be multiplied, will 

 give this mode the preference. 



The question very naturally arises, to what metals is this pro- 

 cess applicable ? We believe we are warranted by the present 

 state of our knowledge, in stating that it has hitherto been applied 

 successfully to copper alone, although no reasonable doubt can be 

 entertained that modes will yet be discovered by which it can be 

 profitably used with other metals. Platinum has been thus pre- 

 cipitated from its chloride, not in a useful form, but in the state 

 of minute division, in a black powder, resembling spongy plati- 

 num. This result is the more to be regretted, since we are in 

 great need of new and economical modes of working this invalu- 

 able metal. Gold and silver may be also thrown down from their 

 respective chloride, and nitrate ; but the film deposited is very 

 thin, and may be removed by rubbing with the finger, and 

 ceases to be deposited when the surface on which it is produced 

 is entirely covered. We were indeed informed, a few months 

 since, that M. De La Rive had furnished the artists of Geneva 

 with a modification of this process, whereby they were able to 

 gild spoons and other articles of silver successfully. But we un- 

 derstand that more was expected from it than has been realized. 

 Lead may be treated in this way, but it is so readily worked in 

 other modes, that it presents no object. 



We have observed in numerous experiments on this subject, 

 that not only the thickness of the porous diaphragm, but also the 

 nature of its surface, influences the rapidity and character of the 

 deposited copper. Thus in using a plaster division, formed in 

 a stone pot, as shewn in fig. 2, by casting between two boards, 

 the surfaces of the division became perpendicularly striated by the 

 grain of the wood, and by little prominences on the lower end, 

 as left by the saw. These strite were apparent on the deposit, 

 giving it the appearance which metals receive from the rolling 

 cylinder — and they were very bold when the copper had attained 

 the thickness of a dollar. Calf-skin gave no such result; on 

 the contrary, the surfaces of deposits obtained with that sub- 

 stance as a division were quite smooth. Bladder-skin, undressed, 

 causes the deposit to be pitted with little hollows and correspond- 



