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 sulphurous 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.

757. Sulphuric acid.—­I have already given my reasons for concluding that sulphuric acid is not electrolyzable, i.e. not decomposable directly by the electric current, but occasionally suffering by a secondary action at the cathode from the hydrogen evolved there (681.).  In the year 1800, Davy considered the sulphur from sulphuric acid as the result of the action of the nascent hydrogen[A].  In 1804, Hisinger and Berzelius stated that it was the direct result of the action of the voltaic pile[B], an opinion which from that time Davy seems to have adopted, and which has since been commonly received by all.  The change of my own opinion requires that I should correct what I have already said of the decomposition of sulphuric acid in a former series of these Researches (552.):  I do not now think that the appearance of the sulphur at the negative electrode is an immediate consequence of electrolytic action.

  [A] Nicholson’s Quarterly Journal, vol. iv. pp. 280, 281.

  [B] Annales de Chimie, 1804, tom. li. p. 173.

758. Muriatic acid.—­A strong solution gave hydrogen at the negative electrode, and chlorine only at the positive electrode; of the latter, a part acted on the platina and a part was dissolved.  A minute bubble of gas remained; it was not oxygen, but probably air previously held in solution.

759.  It was an important matter to determine whether the chlorine was a primary result, or only a secondary product, due to the action of the oxygen evolved from water at the anode upon the muriatic acid; i.e. whether the muriatic acid was electrolyzable, and if so, whether the decomposition was definite.

760.  The muriatic acid was gradually diluted.  One part with six of water gave only chlorine at the anode.  One part with eight of water gave only chlorine; with nine of water, a little oxygen appeared with the chlorine; but the occurrence or non-occurrence of oxygen at these strengths depended, in part, on the strength of the voltaic battery used.  With fifteen parts of water, a little oxygen, with much chlorine, was evolved at the anode.  As the solution was now becoming a bad conductor of electricity, sulphuric acid was added to it:  this caused more ready decomposition, but did not sensibly alter the proportion of chlorine and oxygen.