RECENT PROGRESS IN PHYSICS. 393 



given, proportion to that re(j[uired for the hiyer of copper, as Spencer 

 at first stated, has in no respect been confirmed by subsequent experi- 

 ence. Spencer originally intended to fill the traces drawn in a plate 

 thickly coated with varnish, expecting that the galvanic precipitate 

 would adhere firmly to the copper below, and thus serve for printing 

 after the manner of a wood cut ; but he never obtained in this way 

 results of any practical value. The reduced copper would not adhere 

 to the plate until the latter had been acted upon by nitric acid. He 

 had already experimented extensively when he first published his re- 

 searches on the subject. He copied engraved copper-plates by gal- 

 vanism, or pressed them into lead and used the impressions as moulds, 

 covering the engraved plate while warm with wax, which was after- 

 wards carefully wiped off, for the purpose of preventing the adhesion of 

 the deposit; he also made moulds of plaster of Paris and clay, which 

 were coated with boiled linseed oil, and when this was dry, with mastic 

 varnish, and afterwards covered with bronze powder or gold leaf; 

 these moulds were connected with the zinc plate by a copper wire 

 coated with varnish or sealing-wax. 



The original idea of Spencer, to produce types in relief for printing, 

 was afterwards modified by Von Kobell, in Munich. — (Patent of 1841, 

 Dingler's Journal, vol. 95.) He covered a copper-plate thickly with 

 engraver's varnish, which was made to conduct by means of finely 

 powdered and elutriated graphite ; larger places, which were not in- 

 tended to print, (lights,) were separately covered with wax, by means 

 of a brush, and covered with a conducting substance. The entire 

 plate was then covered with copper under the action of the battery. 

 To facilitate the separation, Von Kobell, in previous experiments, 

 already had slightly silvered engraved plates by immersing them in a 

 solution of chloride of silver and common salt. But the same method 

 has been described by Palmer, under the name of Glyphography, in 

 volume 95 of Dingier. 



Afterwards the apparatus, when no separate decomposing cell was 

 used, was, according to Jacobi's direction, arranged in the following 

 manner : I'he zinc was placed horizontally upon pieces of wood or 

 glass, in a wooden or glass vessel, the bottom of which was formed in 

 the smaller ones of bladder, and in the larger ones of stronger animal 

 membrane, or even of tanned calf skin. This vessel was set in 

 another larger one, and suitably supported at a distance of one to 

 four inches from its bottom ; upon a copper-plate in the larger vessel 

 the plate to be covered was laid, after it had been carefully greased, 

 and wiped off, or silvered. The edge of the lower plate, so far as not 

 covered by that serving as a mould, was coated with wax. To it were 

 soldered, according to its size, one or more copper wires covered with 

 wax, dipping into mercury cups, into which were led an equal number 

 of wires connected with the zinc. In this way the apparatus could 

 easily be taken apart for inspection when required. The zinc was 

 immersed in very dilute sulphuric acid, as in Daniell's battery, and 

 the mould in a solution of sulphate of copper, kept saturated by pow- 

 dered crystals suspended in a bag. Into moulds of plaster of Paris, or 

 clay, wires were fastened, which were covered with wax to prevent 



