Electrography. 159 



its position and thickness may be regulated at pleasure, by two 

 boards fitting tlie sides of the vessel and leaving the desired space 

 between them ; after the plaster has become firm, the boards may 

 be withdrawn. Any of the substances before named will answer 

 to form this division. C, D, the two chambers formed by the divis- 

 ion B, b. Either of these may be devoted to the cupreous solu- 

 tion, and the other to the saline or acid water. The connecting 

 wire will then form an arch between the two, supported by a strip 

 of wood laid over the division. Mr. Joseph Saxton, of the Uni- 

 ted States Mint, showed us one of these little pots which had been 

 sawn down by a stone-cutter's saw, in the line B, 6, and into the 

 slit so formed, a piece of calf-skin was inserted and the joint se- 

 cured from leakage by a hoop of iron, fitted with a binding screw.* 



These two forms of apparatus will be found quite sufficient to 

 copy most objects of art except large engraved plates, which must 

 be provided with a box suited to their form and dimensions.f 



Being provided with such an apparatus as has been described, 

 the next question is, how to make use of it in copying any ob- 

 ject of art ; to accomplish this, the experimenter must proceed 

 as follows : — First, of metalhc medals. A concave copy of the 

 medal must be first obtained, either by fusible metal, or by im- 

 pressing it on soft and bright sheet lead, in a press of sufficient 

 power to strike up its most delicate lines boldly. This prelimi- 

 nary step is not indispensable, because the object to be copied 

 may be at once immersed in the cupreous solution, and a deposit 

 obtained on it, which must subsequently be removed, and used 

 as a mould, in which to cast the relief; but it is obvious that 

 twice the time is required in this way, to obtain the final copy, 

 beside the danger of injuring the beauty of the medal by solder- 

 ing the connection on it, however adroitly that operation may be 

 performed ; and the deposited copper is much more difficult to re- 

 move from a bed of the same metal, particularly if the matrix 

 was itself the result of Voltaic casting. But in whatever manner 

 the intaglio copy may have been obtained, before immersing it in 

 the cupreous solution, all those parts of the surface not intended 

 to be copied, must be covered with bees' wax or varnish, applied 



* Mr. Saxton has by this mode, copied a Daguerreotype plate ; the picture being 

 visible by the difference of polish in the deposit. This is the strongest proof of 

 the great delicacy of this process which has come to our knowledge. 



I See Mr. Spencer's book, p. 47, for a good form of apparatus for this purpose. 



