80 ANNUAL OF SCIENTIFIC DISCO VEBY. 



ink on a steel plate, and the plate is then plunged into a saturated 

 solution of sulphate of copper containing 10 per cent of nitric acid. 

 By the action of the steel the copper is reduced from the sulphate, 

 and all portions of the steel plate not protected by the ink are in- 

 stantly covered with a coating of metallic copper, which protects the 

 steel from the action of the nitric acid. The acid soaks away the 

 ink, and dissolves the steel, forming channels beneath the lines. 

 But as the acid soaks away the ink it is followed by the copper solu- 

 tion, and a coating of metallic copper is deposited within the lines, 

 protecting them from the further action of tne acid. As the copper is 

 deposited first at the edges of the lines, all action of the acids upon 

 the sides of the channels is prevented, and as the acid continues its 

 work longest towards the middle of the line, the channels are made of 

 "V" form, which is precisely the form desired by the engraver. 



In the old method it was necessary to remove the plate from the 

 bath as soon as the finest lines were etched, and to cover these parts 

 with wax to prevent the further action of the acid ; and the plate 

 required to be removed as many times as there were variations of 

 shade in the engraving. But by M. Vial's process the copper is de- 

 posited first in the finest lines, while the action of the acid continues 

 longest in those which are widest. Thus the depth of the engraving 

 is proportioned exactly to the breadth and thickness of the ink-mark, 

 and this by a single immersion of the plate in the bath. The process 

 occupies but five minutes. The copper is removed by ammonia 

 before the plate is used for printing. 



Old engravings may be reproduced by this process by transferring 

 the picture to the steel plate, or the design may be first drawn upon 

 paper and then transferred. 



Additional Improvements. Some curious experiments in engrav- 

 ing, executed before the Emperor of France, by M. Dulos, are thus 

 described in Galignani's Messenger. A sheet of copper, drawn on 

 with lithographic ink, is subjected to the voltaic pile, by which it 

 receives a deposit of iron on those parts not covered by the ink. 

 The ink is then removed by means of benzine, and the sheet is then 

 in the state of an engraved copper-plate, that is, the design is sunk 

 into the plate, and the deposit of iron constitutes the lights. The 

 plate is now dipped into a bath of cyanide of silver, under the action 

 of the galvanic current. Silver is deposited on the copper and not 

 on the iron. The plate is then taken out, and mercury poured upon 

 it. Now, since mercury exercises no action on iron, it can only 

 attack the silver which has filled up the lines originally made with 

 lithographic ink. Hence, where those lines are, we now see mor- 

 cury standing up in relief. Plaster of Paris is now poured over the 

 plate in this condition, and thereby an impression is obtained in 

 which the reliefs made by the mercury are reproduced hollow. 

 (Why the ink was removed, or silver deposited in this case, is not 

 clearly stated.) By the aid of the pile, copper may be deposited on 

 this impression, and the hollows will then come out again in relief. 

 One thus obtains not only a plate which may be printed from, but a 

 matrix which will give an indefinite number of plates. For topo- 

 graphic engraving, the sheet of copper, after being drawn upon, 

 receives a coating of silver, which only goes upon the met.d, leaving 



