752. Nitric acid.—­When very strong, it conducted well, and yielded oxygen at the positive electrode.  No gas appeared at the negative electrode; but nitrous acid, and apparently nitric oxide, were formed there, which, dissolving, rendered the acid yellow or red, and at last even effervescent, from the spontaneous separation of nitric oxide.  Upon diluting the acid with its bulk or more of water, gas appeared at the negative electrode.  Its quantity could be varied by variations, either in the strength of the acid or of the voltaic current:  for that acid from which no gas separated at the cathode, with a weak voltaic battery, did evolve gas there with a stronger; and that battery which evolved no gas there with a strong acid, did cause its evolution with an acid more dilute.  The gas at the anode was always oxygen; that at the cathode hydrogen.  When the quantity of products was examined by the volta-electrometer (707.), the oxygen, whether from strong or weak acid, proved to be in the same proportion as from water.  When the acid was diluted to specific gravity 1.24, or less, the hydrogen also proved to be the same in quantity as from water.  Hence I conclude that the nitric acid does not undergo electrolyzation, 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.

753. 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.

754. Nitrate of ammonia, in aqueous solution, gives rise to secondary results very varied and uncertain in their proportions.

755. Sulphurous acid.—­Pure liquid sulphurous acid does not conduct nor suffer decomposition by the voltaic current[A], 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.

  [A] See also De la Rive, Bibliotheque Universelle, tom. xl. p. 205; or
  Quarterly Journal of Science, vol. xxvii. p, 407.

756.  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