NATURAL PHILOSOPHY. 211 



of impressions. M. Devincenzi observes that lithographic presses and copper 

 plates throw off variously two, three, four, or five hundred copies in a day : 

 with Ms electrographic plates he has hitherto not attempted to produce more 

 than three thousand within the same space, but considering the properties of 

 zinc, and analogous facts, he is of opinion that any number of copies could be 

 printed. Zinc, he says, is as hard as copper, and with copper stereotypes 

 millions of impressions may be struck off, nor is there any reason for sup- 

 posing that zinc stereotypes would prove less serviceable. In its relation to 

 wood engraving, M. Devincenzi demonstrates a manifest advantage on the 

 side of electrography, as regards the more direct application of the latter. 

 In the art of xylography recourse is had both to the engraver and the 

 draughtsman. In electrography the work of the draughtsman is not more 

 difficult, while that of the engraver disappears, and the extraordinary degree 

 of perfection which can be obtained, together with the surprising celerity with 

 which it can meet the various exigencies of the moment, cannot fail to add to 

 its importance. Finally, electrography offers precisely the same facilities in 

 its execution as lithography, and exceeds it illimitably in its power of pro- 

 duction; and, comparing it with line engraving, electrography has ah 1 the 

 advantages of a far more facile execution, of a greater variety of style, result- 

 ing from the use of crayons, of a typographical use of the press, and of a faith- 

 ful reproduction of the artist's labor. 



We append to this notice of M. Devincenzi's invention, an extract from the 

 Report made by the Committee appointed by the Academy of Sciences to 

 inquire into its merits, and test its practicability : 



" The process of engraving in relief, of which we now report, fulfils the 

 object proposed by M. Devincenzi, that of superseding engraving on wood 

 by engraving on zinc. In the former, a draughtsman and an engraver are 

 necessary ; in the latter, a draughtsman only. In comparing this process with 

 that of lithography, either on stone or zinc, we find this great advantage 

 that the printing by electrography is very considerable as to numbers, and 

 costs very little, while the other mode is very limited and dear." 



Engraving by Light and Electricity. M. Pretsch, late manager of the 

 Imperial Printing Office at Vienna^ in a recent paper read before the Society 

 of Arts, London, described a process, by which he obtains, on a glass or other 

 plate, covered with glutinous substances, mixed with photographic materials, 

 a raised or sunk design, which may be copied by the electrotype process so as 

 to produce plates for printing purposes. His process is based on the action 

 of light on a film of glue mixed with bichromate of potash, nitrate of silver, 

 and iodide of potassium. After exposure, the plate is washed with water, a 

 solution of borax, or carbonate of soda. The image then comes out in relief. 

 TVhen the image is thus sufficiently developed, the plate is washed with 

 spirits of wine, then covered with copal varnish, which is afterwards removed 

 with spirits of turpentine, and then the plate is immersed in a weak solution 

 of tannin. It is then ready for copying by the electrotype process. A sunk 

 design is produced by a slight warmth being used after washing with the 

 spirits of wine. 



