Prof, von Kohell vpon Gahanography. 227 



As it has been my object to render the production of these 

 plates dependent as httle as possible on the attention of the ex- 

 perimenter, and on the dexterity of his manipulation, I have 

 selected the process which admitted of the simplest and most con- 

 venient form of the apparatus employed. 



1. The galva?iic apparatus. — The apparatus which I employ 

 consists of a simple circuit. The various parts of which it is 

 composed are — 



(1.) A vessel of well burnt clay, with a flat bottom, whose 

 sides are from five to six inches high. The interior of this vessel 

 is to be coated with a mixture of wax and asphaltum. The di- 

 mensions of the vessel depend upon the size of the plates it is pro- 

 posed to form. Those which I have hitherto used were circular, 

 and about eighteen inches in diameter. 



A vessel suitable for large plates may also be employed for 

 small ones. Vessels of glass or china would of course be prefer- 

 able to clay ones. They may likewise be made of copper, in 

 which case, however, they must receive a coat of good tenacious 

 varnish. 



(2.) A parchment tamborine, with a wooden frame, standing 

 on three feet, about an inch or an inch and a half high. The 

 rim or hoop of the tamborine is about two inches high. What 

 answers, however, better than this, is a sugar-basin of a suitable 

 size, cut off at the proper height, and with parchment stretched 

 upon it. It is to be placed on a tripod rendered insulating by the 

 application of a coat of wax, or it may be suspended by wires in 

 the outer vessel. Instead of parchment, two ox-bladders, one 

 stretched over the other, may be used. The tamborine should 

 be large enough to take in the whole of the plate to be prepared ; 

 it may, however, be larger. 



(3.) A plate of copper, on which the painted plate is to rest. 

 This plate must be half an inch or an inch wider in every direc- 

 tion than the painted plate, and should terminate in one or two 

 strips of copper, an inch and a half wide and five inches long. 

 These strips are to be bent up at a right angle. 



(4.) A zinc plate to be put into the tamborine, and supported 

 above the parchment by a glass rod, about one third of an inch 

 thick, bent into a square or a triangle. The plates I have hitherto 

 used were of rolled zinc, and one twelfth of an inch thick. In 

 my earlier experiments I used to amalgamate them, but now I 

 do not. 



