enter within the pale of the law already described
(380. 412.), by which liquidity is so generally required for conduction and
decomposition. In assuming the solid state of sulphate of baryta, these
bodies became virtually non-conductors to electricity of so low a tension
as that of the voltaic battery, and the power of the latter over them was
almost infinitely diminished.

[A] Philosophical Transactions, 1807, p. 25, &c.

552. The theory I have advanced accords in a most satisfactory manner with
the fact of an element or substance finding its place of rest, or rather of
evolution, sometimes at one pole and sometimes at the other. Sulphur
illustrates this effect very well[A]. When sulphuric acid is decomposed by
the pile, sulphur is evolved at the negative pole; but when sulphuret of
silver is decomposed in a similar way (436.), then the sulphur appears at
the positive pole; and if a hot platina pole be used so as to vaporize the
sulphur evolved in the latter case, then the relation of that pole to the
sulphur is exactly the same as the relation of the same pole to oxygen upon
its immersion in water. In both cases the element evolved is liberated at
the pole, but not retained by it; but by virtue of its elastic,
uncombinable, and immiscible condition passes away into the surrounding
medium. The sulphur is evidently determined in these opposite directions by
its opposite chemical relations to oxygen and silver; and it is to such
relations generally that I have referred all electro-chemical phenomena.
Where they do not exist, no electro-chemical action can take place. Where
they are strongest, it is most powerful; where they are reversed, the
direction of transfer of the substance is reversed with them.

[A] At 681 and 757 of Series VII, will be found corrections of the
statement here made respecting sulphur and sulphuric acid. At present
there is no well-ascertained fact which proves that the same body can
go directly to _either_ of the two poles at pleasure.--_Dec. 1838._

553. _Water_ may be considered as one of those substances which can be made
to pass to _either_ pole. When the poles are immersed in dilute sulphuric
acid (527.), acid passes towards the positive pole, and water towards the
negative pole; but when they are immersed in dilute alkali, the alkali
passes towards the negative pole, and water towards the positive pole.

554. Nitrogen is another substance which is considered as determinable to