130 On the Art of Aquatinta Engraving. 



the conducting wires of a pile held in the flame of a taper 

 were covered with figures of soot, which on the negative 

 wire look the form of a ve2;etation, and on the positive wire 

 a different form. It was to be supposed from this that all 

 Galvanic oxidation was accompanied with a sin)ilar phas- 

 nomenon. To assure myself of this, 1 put the two poles 

 of the pile in communication with two solutions of the 

 acetate of lead. On t'lc positive side the oxide of lead was 

 precipitated in a brown colour : on the negative side k was 

 reduced. Tlie oxide took a form similar to the figures of 

 soot of the positive pole ; and the reduced metal formed a 

 beautiful vegetation. The form of the oxide was like the 

 roots of plants. 



In the course of his experiments on the commotion which 

 the mercury experienced, Ritter had remarked that this 

 metal became less liquid on the positive side, and more 

 liquid on the neaaiivc side. I have repealed this experi- 

 ment, and found it confirmed : however, to assure myself 

 still more completely of the existence of the effect, I made 

 the experiment with an amalgamation of lead, which I kept 

 melted under hot water. 1 let the water cool in commu- 

 nication with the poles of the pile, and I rejuarked that 

 towards the positive pole the amalgamation was consoli- 

 dated more quickly than towards the negative. This fact, 

 moreover, agrees with two other ph^enomena observed by 

 Ritter, viz. that the spark of the positive side inflames the 

 leaves of metals, whilst that of the negative side melts 

 ihem ; and that the hydrogen pole excites a sensation of 

 heat, whilst the positive pole does not, but rather excites a 

 sensation of cold. 



XXVIIf. On the Art of Aquatinta Engraving; with a 

 Description of an Apparatus to prevent the Inconvenience 

 which Artists experience from the Fumes which are pro- 



* duced by the Action of the Acid employed in the Process, 



JL HE principal intention of the present article is to describe- 

 the apparatus mentioned in the title. Some of our readers 

 may, however, be gratified by finding along with it some 

 account of the art in which tlie contrivance is proposed to 

 be used. VVe therefore insert here the best description we 

 have yet niet with respecting that branch of engraving, ex- 

 tracted from the ncvy edition of Dr. Rees's Cyclopajdia. 



TIk artof a(]uatinta ua« invented by Le Prince,, a French 

 KU artist. 



