No. VI.] APPENDIX. 173 



two or three points to which I am desirous of drawing the attention of 

 your readers, as they appear to open a new and important field for investi- 

 gation for which I have not the time at present. With regard to the 

 precipitation of the copper, I beg leave to submit a modification of a plan 

 first proposed by Mr. Mason, but I believe also contemporaneously used by 

 other persons, that of making copper form the oxygen side of the battery, 

 which being dissolved is again thrown down at the platina or hydrogen 

 end upon the medal or cast put for its reception. 



The mode which I adopt is, first to obtain a long dish or trough, and 

 then to place a wire in the inside along its bottom, which is connected to 

 the zinc of one of the cells of my battery along the opposite side of the 

 vessel ; a large piece of copper is placed in connection with the silver of 

 the battery, and a solution of sulphate of copper is then added. By this 

 arrangement the current is generated at the zinc, passes to the medal, 

 reduces the copper whilst the oxygen and acid are transferred to the refuse 

 copper, and dissolves a corresponding quantity of copper, and by this 

 means the solution is always kept saturated with the metal. 



When medals are to be copied, they are singly placed in contact with 

 the wire in connection with the zinc of the battery, and in this way many 

 may be done in the same vessel, and either may be taken out and examined 

 without the slightest interruption to the others. The rapidity of the 

 process may be increased without detriment by the use of two to six or 

 even more cells of the battery, as the copper will still be extremely tough. 

 It will be found that my battery will require not the slightest alteration, 

 except once a day, when the liquid should be changed. I have tried other 

 solutions of copper, such as the nitrate : but although the process is 

 hastened, the metal is apt to be brittle, or have other imperfections. 



When engraved plates are to be copied, the first copy is in basso- 

 rilievo, and therefore a second is required to be made which is in " inta- 

 glio," and then ready for printing. Copies may even be taken of non- 

 conducting substances, as woodcuts, &c., by brushing them over with 

 black-lead, taking care that the copper wire is in good contact with the 

 plumbago. 



The great advantages of this mode of proceeding above all others are : 

 first, the quality of the copper is far better than when reduced in the usual 

 way as described by Messrs. Spencer and Solly this advantage is owing 

 to the use of the copper at the oxygen end as suggested by Mr. Mason ; 

 secondly, all the plates or medals, for there is no limit to the number, are 

 in the same vessel ; thirdly, the process may be hurried or retarded, accord- 

 ing as the number of plates of the battery are increased or diminished ; 

 fourthly, the plates will not require to be interfered with till the precipita- 

 tion is completely finished, and there are even many other more trifling 

 advantages which it would be tedious to enumerate. 



The mode of proceeding here detailed differs but little from others 

 which have been described ; but these trifling differences are so important 

 in practice, that this mode will probably supersede every other. In fact, I 

 have had the pleasure of seeing many most valuable copper-plates sub- 

 jected to this process, and the specimen which accompanies this paper I 

 believe is the first which has ever undergone the ordeal of having the large 

 number of impressions, required for any publication, printed from it. Of 



