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.