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 Nobilf 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 o^ridation 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 intensity 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. 
Another experiment wa^ 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 
