Prof, von Kohell upon Galvanography. 223 



It was not long before I obtained results from which I felt 

 convinced that this process might be of importance in the arts, 

 and my attention was therefore directed to removing the diffi- 

 culties and overcoming the imperfections that beset me at first, 

 and I now proceed to lay before the public the results of those 

 endeavors. 



I must here acknowledge with gratitude the gracious support 

 which the king was pleased to afford me for the prosecution of 

 my experiments; neither should I omit to mention that I am 

 indebted to several artists and amateurs of this city, for the assist- 

 ance I received from them by their furnishing me with pictures 

 for my experiments. I am also under obligations to my col- 

 league, Prof von Steinheil, for many friendly communications. 

 The first pictures were painted by Auer, and by Counts Pocci 

 and Spreti. 



Before entering upon the subject in detail, it will perhaps not 

 be out of place to say a few words upon the galvanic process in 

 general, as far as we shall have to enter upon it in the following 

 pages. 



If a plate be laid in a tamborine and some water acidulated 

 with a few drops of sulphuric acid be poured on it, and if then 

 this tamborine be placed in a copper vessel filled with a solu- 

 tion of sulphate of copper, no action is observed to take place 

 between the copper and the zinc, nor is there any change noticed 

 in the sulphate of copper. As soon however as the copper vessel 

 is brought into connection with the zinc plate by means of a 

 strip of metal, the zinc plate will begin to be consumed, and 

 metallic copper will be thrown down from the metallic salt in 

 solution, on to the copper vessel. The contact of the hetero- 

 geneous metals above mentioned, develops therefore in the cir- 

 cumstances in question, a force manifested by the decomposition 

 of the sulphate of copper, and this force is termed a galvanic cur- 

 rent. By this force, both the sulphate of copper (consisting of 

 sulphuric acid, oxide of copper and water) and also the water of 

 the solution are decomposed, the sulphuric acid of the sulphate 

 of copper and the oxygen of the water passing through the 

 membrane to the zinc, while the oxide of copper and the hy- 

 drogen of the water are carried to the copper of the vessel. 

 The hydrogen, however, reduces the oxide of copper to a me- 

 tallic state by combining with its oxygen to form water, and 



