314 M. Nobili on New Electro-Chemical Phenomena. 



which is surrounded by an area of different colours which are 

 feeble. The dark circle does not acquire its proper tint till 

 the instant that we interrupt the circuit. One would say that 

 the veil which covers the exterior circle is folded back from 

 the centre, at the moment when the action of the current 

 ceases. As I have seen this phenomenon only with acetate of 

 potash, it merits the attention of philosophers. 



Acetate of Copper and Lead mixed together. — On 

 Gold and Platina Positive there appears the finest coloured 

 rings, as with acetate of lead alone. Is this salt, therefore, 

 the only one which enjoys the property of colouring, in this 

 manner, these two metals which are the most difficultly oxida- 

 ble ? But if these coloured rings proceed, as they appear to 

 do, from some of the electro-negative substances in the solu- 

 tion which deposit themselves in thin films on the surface of 

 these two metals, why does it not happen with other metals ? ; 



Upon Silver Negative there is formed a great number of 

 concentric circles, which are generally arranged as follows : 

 Jn the centre is a dark circle, then a yellow circle bordering 

 upon red, then a deep black circle, then a fine ring of pure 

 copper, then a circle less black than the third ; and, lastly, a 

 zone of a light coppery tint. A stratum of nitric acid passed 

 over this series of circles, discovers in the centre a spot having 

 the lustre of silver surrounded with four circles of copper in 

 the state of oxide and metal, alternating in the ordinary man- 

 ner, and becoming more distinct by a second wash of nitric 

 acid. 



Antimoniated Tartrate of Potash, or tartar emetic. — 

 On Silver Positive there appears five coloured circles. The 

 first in the centre is dark, the second is a silvery white, the 

 third is azure .bordering upon violet, the fourth is silvery 

 white, and the fifth is violet, but light without. 



Upon Silver Negative there are five other circles. The 

 first is black, the second reddish-yellow, the third black, the 

 fourth a bright blue, and the fifth slightly deep. 



Chlorate of Platina. — On Silver Positive there is a 

 black spot in the centre, then a circle of an ash colour, then a 

 slight iris. On silver negative there is a black spot in the 

 centre, surrounded with a bright circle, then a circle more 



