726.  A third form of experiment, in which difference of intensity was obtained, for the purpose of testing the principle of equal chemical action, was to arrange three volta-electrometers, so that after the electric current had passed through one, it should divide into two parts, each of which should traverse one of the remaining instruments, and should then reunite.  The sum of the decomposition in the two latter vessels was always equal to the decomposition in the former vessel.  But the intensity of the divided current could not be the same as that it had in its original state; and therefore variation of intensity has no influence on the results if the quantity of electricity remain the same.  The experiment, in fact, resolves itself simply into an increase in the size of the electrodes (725.).

727.  The third point, in respect to which the principle of equal electro-chemical action on water was tested, was variation of the strength of the solution used.  In order to render the water a conductor, sulphuric acid had been added to it (707.); and it did not seem unlikely that this substance, with many others, might render the water more subject to decomposition, the electricity remaining the same in quantity.  But such did not prove to be the case.  Diluted sulphuric acid, of different strengths, was introduced into different decomposing apparatus, and submitted simultaneously to the action of the same electric current (714.).  Slight differences occurred, as before, sometimes in one direction, sometimes in another; but the final result was, that exactly the same quantity of water was decomposed in all the solutions by the same quantity of electricity, though the sulphuric acid in some was seventy-fold what it was in others.  The strengths used were of specific gravity 1.495, and downwards.

728.  When an acid having a specific gravity of about 1.336 was employed, the results were most uniform, and the oxygen and hydrogen (716.) most constantly in the right proportion to each other.  Such an acid gave more gas than one much weaker acted upon by the same current, apparently because it had less solvent power.  If the acid were very strong, then a remarkable disappearance of oxygen took place; thus, one made by mixing two measures of strong oil of vitriol with one of water, gave forty-two volumes of hydrogen, but only twelve of oxygen.  The hydrogen was very nearly the same with that evolved from acid of the specific gravity 1.232.  I have not yet had time to examine minutely the circumstances attending the disappearance of the oxygen in this case, but imagine it is due to the formation of oxywater, which Thenard has shown is favoured by the presence of acid.

729.  Although not necessary for the practical use of the instrument I am describing, yet as connected with the important point of constant chemical action upon water, I now investigated the effects produced by an electro-electric current passing through aqueous solutions of acids, salts, and compounds, exceedingly different from each other in their nature, and found them to yield astonishingly uniform results.  But many of them which are connected with a secondary action will be more usefully described hereafter (778.).