138	Faraday's Researches
the nitric acid does not undergo electrolysation, but the water
only; that the oxygen at the anode is always a primary result,
but that the products at the cathode are often secondary, and
due to the reaction of the hydrogen upon the nitric acid.
 488.	Nitre.—A solution  of this  salt yields very variable
results, according as one or other form of tube is used, or as
the electrodes are large or small.    Sometimes the whole of the
hydrogen of the water decomposed may be obtained at the
negative electrode; at other times, only a part of it, because of
the ready formation of secondary results.   The solution is a
very excellent conductor of electricity.
 489.	Nitrate of ammonia, in aqueous solution, gives rise to
secondary results very varied and uncertain in their proportions.
 490.	Sulphurous acid.—Pure liquid sulphurous acid does not
conduct nor suffer decomposition by the voltaic current,1 but,
when dissolved in water, the solution acquires conducting power
and is decomposed, yielding oxygen at the anode, and hydrogen
and sulphur at the cathode.
 491.	A solution containing sulphuric acid in addition to the
sulphurous acid was a better conductor.    It gave very little
gas at either electrode:  that at the anode was oxygen, that at
the cathode pure hydrogen.    From the cathode also rose a white
turbid   stream,  consisting  of  diffused   sulphur,  which  soon
rendered the whole solution milky.   The volumes of gases were
in no regular proportion to the quantities evolved from water
in the voltameter.    I conclude that the sulphurous acid was not
at all affected by the electric current in any of these cases, and
that the water present was the only body electro-chemically
decomposed;   that, at the anode, the oxygen from the water
converted the sulphurous acid into sulphuric acid, and, at the
cathode, the hydrogen electrically evolved decomposed the sul-
phurous acid, combining with its oxygen, and setting its sulphur
free.   I conclude that the sulphur at the negative electrode
was only a secondary result;  and, in fact, no part of it was
found combined with the small portion of hydrogen which
escaped when weak solutions of sulphurous acid were used.
 492.	Sulphuric acid.—I have already given my reasons for
concluding that sulphuric acid is not electrolysable, i.e. not
decomposable directly by the electric current, but occasionally
suffering by a secondary action at the cathode from the hydrogen
evolved there (416).   In the year 1800, Davy considered the
1 See also De la Rive, Bibliothlque Universelle, torn. xl. p. 205;   or
Quarterly Journal of Science, vol. xxvii. p. 407.