316 M. Nobili on New Electro-Chemical Phenomena. 



are easily dissipated by the action of heat ; while, towards the 

 centre, the deposit is much more considerable, but from its 

 very abundance there is formed a species of crust, which 

 splits by the heat, and is easily detached from the metal. 



On Copper Positive there is an alternation of clear and dark 

 circles. 



On Brass Positive there are different concentric circles, 

 which, when cleaned with linen, exhibit three or four rings al- 

 ternately red and yellow. The red ones proceed from the cop- 

 per in the brass, which then loses the zinc in its composition. 

 There was no appearance upon tin and platina positive. 



Sulphate of Soda. — On Silver Positive there are five 

 small concentric circles ; in the centre there is a black point, 

 then a bright blue circle, then two dark circles, separated by 

 a bright one. 



Urine. — Upon Silver Positive there are different orders 

 of very brilliant coloured rings round a dark centre. When 

 dried, they are permanent, in contact with the air. 



Urea acts like the preceding, but produces colours more 

 definite. 



Urine and Common Salt. — Upon Silver Positive the phe- 

 nomenon is the same as in the preceding case, But the colour- 

 ed rings, being more numerous, are also more delicate. When 

 exposed to heat, they take a fine red colour, without produ- 

 cing any confusion among their shades. On platina positive 

 there is no effect, and on brass and copper positive there is a 

 small number of insignificant circles. • 



These experiments, which have not been pushed farther, 

 lead to two results. The first is the property, which certain 

 electro-negative substances possess, of attaching themselves, in 

 certain determinate circumstances, to the surface of some of 

 the less oxidable metals, in films so thin and regular, as to pro- 

 duce, in a thousand varied forms, the elegant phenomenon of 

 coloured rings. The arts will probably avail themselves of 

 this new colouring process, and may perhaps succeed in apply- 

 ing it to the ornament of some objects of luxury. When the 

 electro-negative substances are not deposited on the metals in 

 their films, they generally attack their surface, not in a uni- 

 form manner, or, as we might at first suppose, by a continued 



