94 Faraday's Researches

depended upon the character of the matter previously soili
the plates, and which may easily be supposed to be sometirr
of such a nature as to be removed by these acids, and at otl
times not. Weak sulphuric acid showed the same differeii'
but strong sulphuric acid (337) never failed in its action.

341. The most favourable treatment, except that of maki
the plate a positive pole in strong acid, was as follows. T
plate was held over a spirit-lamp flame, and when hot, rubt
with a piece of potassa fusa (caustic potash), which meltis
covered the metal with a coat of very strong alkali, and t
was retained fused upon the surface for a second or two: 1
was then put into water for four or five minutes to wash off 1
alkali, shaken, and immersed for about a minute in hot strc
oil of vitriol; from this it was removed into distilled wat
where it was allowed to remain ten or fifteen minutes to remc
the last traces of acid (318). Being then put into a mixti
of oxygen and hydrogen, combination immediately began., a
proceeded rapidly; the tube became wafm, the platina beca
red hot, and the residue of the gases was inflamed. This efi
could be repeated at pleasure, and thus the maximum phe:
menon could be produced without the aid of the voltaic batte

342. When a solution of tartaric or acetic acid was substitut
in this mode of preparation, for the sulphuric acid, still
plate was found to acquire the same power, and would of
produce explosion in the mixed gases; but the strong sulphi
acid was most certain and powerful.

343. If borax, or a mixture of the carbonates of potash ,•
soda, be fused on the surface of a platina plate, and that p]
be well washed in water, it will be found to have acquired
power of combining oxygen and hydrogen, but only ii
moderate degree; but if, after the fusion and washing, it
dipped in the hot sulphuric acid (337), it will become \
active.

344. Other metals than platina were then experimented \\
Gold and palladium exhibited the power either when made
positive pole of the voltaic battery (306), or when acted or
hot oil of vitriol (337). When palladium is used, the ac
of the battery or acid should be moderated, as that met-
soon acted upon under such circumstances. Silver and coj
could not be made to show any effect at common temperati

1 The heat need not be raised so much as to make the alkali tarnis!
platina, although if that effect does take place it does not preven^
ultimate action.nfer the property it is only by the destruction or