120 J. Waterbouse — The Application of Pliofogra^iliy [No. 2, 



The surface of the stone is made as level as possible and carefully 

 polished, it is then washed with an 8 per cent solution of chloride of cal- 

 cium and dried. A 12 per cent solution of nitrate of silver is then washed 

 over the stone in the dark, and when dry it is exposed to ligbt under a 

 reversed negative. The print is fixed with a 20 per cent solution of hypo- 

 sulpbite of soda, and then well washed witb plenty of water to remove 

 all traces of the hyposulphite. 



This method is used at tbe Topographical Department at the Hague 

 to give tbe ground-work for the beautifully engraved cbromo-lithograpbed 

 maps of the Dutch Netherlands, and for the reproduction of photograpbs 

 of Dutch artillery material, by a similar system of engraving upon stone 

 permitting several shades of the same tint to be printed from one 

 stone.* 



'Photographing on Copper, — A photographic image may also be ob- 

 tained upon a copper plate by tbe following method, proposed by M. Mialeret, 

 which may be of use to engravers in giving them an accurate image of 

 their subject to work upon.f 



The copper plate, being well cleaned and ready for engraving, is plunged 

 into a solution of 



Sulphate of Copper, 125 parts. 



Sea Salt, 75 „ 



Water, 960 „ 



and allowed to remain for about a minute, it is then taken out of the bath, 

 well washed and polished with a soft cloth. It is next exposed to light for 

 about 5 or 10 minutes under a reversed negative, or even under a paper 

 print on thin paper, care being taken that the design appears reversed on 

 the plate. The plate is then removed from the printing-frame and plunged 

 into a 20 per cent solution of hyposulphite of soda containing a little chlo- 

 ride of silver. After a few seconds the ground whitens, while the design 

 becomes of a deep black. The plate is then taken out and well washed. 

 The black deposit forming the shades may be removed or allowed to remain, 

 in which case the plate should be varnished. It is said that these images 

 may be etched by the use of menstrua which will attack the copper without 

 affecting the silver, but I have not been successful in this application of 

 the process. 



XI. CoNCLrDiNG Eemaeks. 

 Having now described the different processes most capable of being 

 utilised by the cartographer, it may be as well to briefly sum up the cases 

 in which they are applicable, and to indicate the direction in which improve- 

 ments should be looked for. 



* ' Report on the Cartographic Applications of Photography* p. 58. 

 t '' Photographic News,' Vol. X, p. 190. 



