56 Mr. Warington on the coloured Films 
layer which is thus coloured a suboxideP In a foot-note at 
p. 110, we read, “Berzelius was more sensible of the diffi- 
culty,” (of accounting for these coloured films) “ perhaps, 
than any one else : but would not an open avowal have been 
better than the attempt to evade it by the adoption of the 
term suboxide, which is quite as vague and undefined as the 
'principle of oxidation^ for which it was offered as a substitute?” 
This is rather strong language to be used against such an au- 
thority as Berzelius, every one of whose statements is backed 
by investigation, and brought by Prof. Nobili, who does not 
adduce a single experiment in proof of his statements. But 
to proceed : “ I have always entertained some doubts as to 
the correctness of this explanation ; because each degree of 
oxidation has a colour peculiar to itself, and in no way re- 
lated to that variety of tints of which we speak. I was also 
struck by the well-known practice of giving steel a violet colour 
in order to secure it from rust.” “ Were this tint, as it is pre- 
sumed to be, the effect of oxidation, it would, in my opinion, 
instead of preventing, serve only to accelerate oxidation.” 
“ But this is not all ; the superficial colours of which we speak 
are changeable, and belong evidently to the same class as 
those produced by thin plates. Now the pure metals are, 
from their opacity, incapable of this species of coloration. 
Can they acquire that capacity in their first degree of oxida- 
tion by becoming suddenly transparent in consequence of their 
union with a small quantity of oxygen ? The hypothesis far 
exceeds the bounds of probability, and the phaenomenon re- 
quires to be otherwise explained.” Again, “ Confining my- 
self in this place to the colours produced on metals by the 
action of fire, I do not hesitate to say, that I think their 
origin now placed beyond the reach of doubt. It may be 
safely laid down as a general proposition, that the oxygen of 
the atmosphere produces them, not, as is supposed, by oxi- 
dizing the surface of the metal, but by becoming fixed in the 
form of a thin plate or film, similar to those of the electro- 
chemical appearances.” Professor Nobili then gives a detail 
of the production of the colours by heat, and observes, that 
as long as the colours are seen there is no oxidation, but that 
when the metal loses its brilliancy and lustre it has become 
oxidized, and that if removed from the heating medium be- 
fore this effect takes place, the oxygen will cover the metal 
and adhere as a varnish. 
In Berzelius’s System of Chemistry, under the heads of the 
various metals and the action of heat upon them, he states 
distinctly, that copper, lead, and tin form protoxides, and that 
palladium forms a suboxide; so that out of four metals which 
