4 Correction of JSngraved plates hij Electro-deposition. [Jan. 



about li inch deep and corresponding in size to the extent of the required 

 corrections is made on the plate by means of a strip of bordering wax and the 

 plate is placed in a level position upon wooden blocks. The trough having 

 been filled with a solution of sulphate of copper, one or more small cylindrical 

 porous cells about 2" high and 1" in diameter are placed in position a few 

 inches from the cuts ; their number varying according to the extent of the 

 corrections. A rod of zinc to which is attached a copper band, is placed in 

 each ceil, the free end of this copper band being attached to the uncoated 

 part of the plate outside the trough, the circuit is completed by pouring a 

 little very dilute sulphuric acid into the porous cell. The deposition of 

 copper in the cuts then commences and in the course of 24i to 48 hours 

 entirely fills them up and forms a ridge of copper all round them. The 

 solution is then poured away, the wax wall and coating are removed and 

 the surface of the plate having been protected by fastening strips of waxed 

 paper round the corrected parts, the superfluous deposit is carefully filed 

 down till it is no thicker than the surrounding paper and the remainder is 

 removed with a sharp engraver's scraper. If this operation is skilfully 

 performed, the surface of the corrected parts should be left perfectly even 

 with the remainder of the plate and without a trace of damage to any of the 

 surrounding work. 



The method used at the Military Geographical Institute in Vienna 

 differs considerably from the above but is equally effective. The engraved 

 plate is first of all silvered by rubbing over it a solution of nitrate of silver 

 in c^^anide of potassium with a little tripoli powder. The parts to be cor- 

 rected are then cut out and the plate placed in the depositing trough of the 

 electrotyping apparatus ordinarily used at the Institute. 



After the lapse of a few days a sheet of copper is deposited over the 

 whole of the plate, and when the deposit is of sufficient thickness to fill up 

 the cuts, the plate is removed from the trough. The deposited metal im- 

 mediately above and around the parts to be corrected is then scraped down 

 with a curved scraper till it is quite thin, when the covering sheet of copper 

 is stripped off the engraved plate, leaving a slightly raised ridge over the 

 corrections, which is removed with the scraper as in M. George's process. 



This method is neither so simple nor so economical as M. George's, and 

 the only advantages it would appear to possess are uniformity and regularity 

 of action, as well as the perfect protection afforded by the deposited sheet of 

 copper to the engraved plate during the removal of the superfluous metal. 



In India, the rapid extension of railways, roads and canals, the frequent 

 revisions of boundaries and the conflicting systems of orthography necessi- 

 tate constant changes during the progress of the engraving of the Sheets of 

 the Indian Atlas, and the necessity for adopting some such plan for making 

 these corrections became apparent a short time ago, when happening to pass 



