164 APPENDIX. [No. V. 



sublimate is still more simple, for here it is only necessary to sponge over 

 a very thin paper with a 20-graia solution of nitrate of silyer, and expose 

 it to the action of the light of the sun. Drawings made in this way have 

 analogy with etchings executed on glass, covered with black varnish, but 

 are more easily made ; the white parts of the paper are, however, not so 

 transparent as the glass. An error requiring notice has also crept into 

 my paper; for the hyposulphates, instead of the hyposulphites, are there 

 mentioned as stopping agents. 



No. V. 



THE PRINCIPLE, CONSTRUCTION, AND USE OF SMBB'S 

 BATTBRT; its tabiotjs Poems, with pull Directions foe 

 ITS Manipttlation, moee especially in the Peocessbs of 

 Blecteo-Metalluegt. (Transcribed from Paper read at the Society 

 of Arts, June 1st, 1840, and from Smee's /Elements of Electro- 

 Metallurgy,' &c.) 



The most valuable instrument which chemists employ for their ana- 

 lytical experiments is, no doubt, the galvanic battery ; but so much trouble 

 attends its use, that, except in the laboratory of the professed chemist, it 

 is not employed to any considerable extent. Experiencing this incon- 

 venience in the experiments which I conducted on the red f errocyanate of 

 potash, it became a matter of the greatest importance to ascertain how far 

 a battery could be constructed, that at once should possess a capability of 

 being used at a moment's notice, and have besides considerable power 

 imited with cheapness of action, and, at the same time, without thei 

 necessity of much laborious cleaning after its employment. 



After experimenting with the batteries before known to the public, I 

 became convinced that it was of the highest importance to supersede the 

 necessity of diaphragms, attended as they are with continual trouble and 

 expense; and as the power of the battery seems to depend upon the 

 facility offered to the evolution of the hydrogen and preventing its 

 adhesion to the negative metal, whereby it is coated as with a varnish, and 

 the action almost entirely destroyed, all my experiments were directed to 

 this object. I first perceived that the gas was not evolved equally from 

 every part of the surface of a smooth piece of platinum, but chiefly from 

 the comers, edges, and points. PoUowing this hint, I roughened the 

 metal with sand-paper and found the evolution of the gas to be increased ; 

 and when the surface of other metals, as silver or iron, was roughened by 

 some acid, I found the gas also to be much increased. Moreover, zinc 

 shavings, which present the singular anomaly of having one surface ex- 

 tremely bright and the other of a delicate frosted appearance, show this 

 property well, gas being .freely given off from the rough, but adhering 

 firmly to the bright surface. The same differences are also observed when 

 rough and polished steel are employed. These experiments induced the 

 idea that spongy platinum, which may be considered as a mass of metaUio 

 points, would be very efficient in forming a galvanic circuit ; and on tiding 



