Bodies which Pass to Either Pole      8 i
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.
 289.	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 (263),, 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.
 290.	Nitrogen is another substance which is considered as
determinable to either pole; but in consequence of the numerous
compounds which it forms, some of which pass to one pole,
and some to the other, I have not always found it easy to
determine the true circumstances of its appearance.   A pure
strong solution of ammonia is so bad a conductor of electricity
that it is scarcely more decomposable than pure water;  but if
sulphate of ammonia be dissolved in it, then decomposition
takes place very well; nitrogen almost pure, and in some cases
quite, is evolved at the positive pole, and hydrogen at the
negative pole.
 291.	On the other hand, if a strong solution of nitrate of
ammonia be decomposed, oxygen appears at the positive pole,
and hydrogen, with sometimes nitrogen, at the negative pole.
If fused nitrate of ammonia be employed, hydrogen appears at
the negative pole, mingled with a little nitrogen.   Strong nitric
acid yields plenty of oxygen at the positive pole, but no gas
(only nitrous acid), at the negative pole.   Weak nitric acid
yields the oxygen and hydrogen of the water present, the acid
apparently  remaining  unchanged.    Strong  nitric   acid   with
nitrate of ammonia dissolved in it, yields a gas at the negative
pole, of which the greater part is hydrogen, but apparently a
little nitrogen is present.    I believe that in some of these cases
a little nitrogen appeared at the negative pole.   I suspect,
however, that in all these, and in all former cases, the appear-
ance of the nitrogen at the positive or negative pole is entirely
f