54) Mr. Warington on the coloured Films 



coloured rings in all its beauty ; Srdly, instead of oxidizing 

 the metal, these electro-negative elements contribute to se- 

 cure it against oxidation in every part to which they are ap- 

 plied. A fact so unprecedented is interesting to chemistry, 

 and is entitled to particular attention, as tending to enrich 

 the science by the introduction of new ideas." 



In a foot-note the following theory is offered, " that the 

 electro-negative elements disposed in thin layers on the surface 

 of the metals are at too great a distance from the molecules of 



• • • 



these substances to enter into combination with them." These 

 extracts, although of no great length, will yet put the reader 

 in possession clearly of Professor Nobili's views of the subject, 

 and enable him to appreciate the bearing of the following ex- 

 periments. 



The "unprecedented fact" then "so interesting to chemistry" 

 is entitled to particular attention, as it tends to enrich the sci- 

 ence, and introduce new ideas. What is this fact? it is the 

 production of coloured films at the positive pole (the poles 

 being of platina) of an electric circuit, the connecting medium 

 being a solution of acetate of lead. These coloured films, Pro- 

 fessor Nobili states, consist of oxygen and acid precipitated, 

 as it were, upon the surface of platina, iron, or steel, without 

 producing any oxidation of these metals, and the correctness 

 of which statement the multiplicity of the experiments, he 

 states, places beyond a reasonable doubt. 



Some of these splendidly coloured films, produced as stated 

 before, were well washed with distilled water and acted upon 

 by dilute nitric acid, which did not remove them, but ap- 

 peared to dilute, as it seemed, the inteftsity and brilliancy of 

 the colours : the solution was decanted and evaporated to dry- 

 ness to remove all excess of acid, and on being tested gave 

 indications of lead. Muriatic acid instantly destroyed all 

 trace of the coloured films with evolution of chlorine gas and 

 the formation of a curdy or crystalline chloride of lead. 

 Anotlier experiment was made by heating the films to red- 

 ness and then acting upon them by dilute nitric or acetic 

 acid, which dissolved them rapidly and yielded the usual in- 

 dications of the presence of that metal. It would appear from 

 these experiments that these electro-chemical appearances are 

 therefore nothing more than extremely thin films of per- 

 oxide of lead or of red lead spread out on the surface of the 

 platina, but from their great tenuity it is likely that they may 

 modify in a degree the action of the acids used. I may be 

 allowed to remark here, that if the voltaic arrangement is too 

 powerful, or the solution of acetate of lead too strong, when 



