22 Professor Grove on a Voltaic Process for Etching 



ferior lustre. On immersion in nitric acid of different degrees 

 of dilution, the plates were unequally attacked, and the etching 

 burred and imperfect. Of the other solutions, hydrochloric 

 acid was, after many experiments, fixed on as decidedly the 

 best: indeed, this I expected, from the strong affinity of 

 chlorine for silver. 



I will now describe the manipulation which has been em- 

 ployed by Mr. Gassiot and myself, in the laboratory of the 

 London Institution, with very uniform success. A wooden 

 frame is prepared, having two grooves at 0*2 of an inch di- 

 stance, into which can be slid the plate to be etched, and a 

 plate of platinum of the same size. To ensure a ready and 

 equable evolution of hydrogen, this latter is platinized after 

 Mr. Smee's method ; for, if the hydrogen adhere to any part 

 of the cathode, the opposite portions of the anode are pro- 

 portionably less acted on. The back and edges of the Da- 

 guerreotype are varnished with a solution of shell-lac, which 

 is scraped off one edge to admit of metallic connexion being 

 established. The wooden frame with its two plates, is now 

 fitted into a vessel of glass or porcelain, filled with a solution 

 of two measures hydrochloric acid, and one distilled water 

 (sp.gr. I'l); and two stout platinum wires, proceeding from a 

 single pair of the nitric acid battery, are made to touch the 

 edges of the plates, while the assistant counts the time ; this, 

 as before stated, should not exceed thirty seconds. When the 

 plate is removed from the acid, it should be well rinsed with 

 distilled water; and will now (if the metal be homogeneous) 

 present a beautiful sienna-coloured drawing of the original 

 design, produced by a film of the oxychloride formed ; — it is 

 then placed in an open dish containing a very weak solution of 

 ammonia, and the surface gently rublied with very soft cotton, 

 until all the deposit is dissolved ; as soon as this is effected, 

 it should be instantly removed, plunged into distilled water, 

 and carefully dried. The process is n.ow complete, and a per- 

 fect etching of the original design will be observed ; this, when 

 printed from, gives a positive picture, or one which has its lights 

 and shadows as in nature ; and which is, in this respect, 

 more correct than the original Daguerreotype as the sides are 

 not inverted ; printing can therefore be directly read, and in 

 portraits thus taken, the right and left sides of the face are in 

 their proper position. There is, however, ex necessitate rei, 

 this difficulty, with respect to prints from Daguerreotypes, — if 

 the plates be etched to a depth sufficient to produce a very 

 distinct impression, some of the finer lines of the original 

 must inevitably run into each other, and thus the chief beauty 

 of these exquisite images be destroyed. If, ou the other hand, 



