1-874.] Correction of Engraved plates ly Mectro-deposition. 5 



through the engraving rooms of the Surveyor General's Office I observed 

 that a plate on which numerous corrections had been made by the ordinary 

 process of " knocking up" was consequently much disfigured by hollows 

 and inequalities all over it, and finding that there was a very valuable plate 

 of hill work, on which a boundary had to be altered, I proposed to try whe- 

 ther this coidd be done by the system I had seen working in Paris, and thus 

 avoid the almost irretrievable damage the plate must otlierwise have sus- 

 tained. 



At first M. George's method was tried, ]?ut not knowing the exact pro- 

 portions of his solutions, nor being able to procure the same kind of porous 

 cells, the early attempts did not succeed very well, and as there appeared to 

 be other difficulties connected with working the single cell system, it 

 occurred to me that the use of a separate battery might give better and 

 more certain results. After a few trials, perfect success was attained by the 

 following method which is scarcely less simple than M. George's, and 

 much more economical than that practised in Vienna, while securing some 

 of its peculiar advantages. 



The engraved plate is prepared almost precisely in the same manner 

 as in M. George's method, i. e., it is first covered with a thin asphaltum 

 varnish, the parts to be corrected are carefully cut out and the remainder 

 of the plate, with the exception of one corner, coated with Brunswick black,* 

 a double coat being given on the part of the plate surrounding the cut to 

 the distance of about 4 or 5 inches. When this coating is thoroughly dry 

 a strip of bordering wax is securely fastened down on the plate at a distance 

 of about 2 or 3 inches all round the parts to be filled in, forming a water- 

 tight trough about 1^ inch deep. (See Plate I.). 



The battery is of the pattern in ordinary use in the Indian Government 

 Telegraph Department known as Menotti's modification of Daniell's battery. 

 It consists of a stoneware jar containing at the bottom a disc of lead 

 or copper to which an insulated copper wire running up the side of the 

 jar is attached. Above the disc of lead is a layer of crystals of sulphate of 

 copper, then some saw-dust covered by a piece of felt over which is placed a 

 thick disc of zinc with a brass binding-screw attached. To set the battery 

 in action, the jar has only to be filled with water, and thus all messing with 

 acids and disagreeable fumes are avoided. The bare corner of the plate 

 and all the connections of the battery having been carefully cleaned, the 

 zinc pole is attached by means of a narrow copper band to the clean corner 

 of the engraved plate. A solution of — • 



Sulphate of copper, 5 parts 



Sulphuric acid, 1 „ 



Water, 30 „ 



* The object of coating the whole plate with Brunswick black is to preserve the 

 surface from injury in case of leakage from the wax trough. 



