DECOMPOSITIONS BY A SINGLE PAIR OF PLATES. 431 



903. Water acidulated with sulphuric acid, solution of muriatic acid, solution of 

 sulphate of soda, fused nitre, and the fused chloride and iodide of lead were not de- 

 composed by this single pair of plates, excited only by dilute sulphuric acid. 



904. These experiments give abundant proofs that a single pair of plates can elec- 

 trolyze bodies and separate their elements. They also show in a beautiful manner the 

 direct relation and opposition of the chemical affinities concerned at the two points of 

 action. In those cases where the sum of the opposing affinities at x was sufficiently 

 beneath the sum of the acting affinities in v, decomposition took place ; but in those 

 cases where they rose higher, decomposition was effectually resisted and the current 

 ceased to pass (891.). 



905. It is, however, evident, that the sum of acting affinities in v may be increased 

 by using other fluids than dilute sulphuric acid, in which latter case, as I believe, it 

 is merely the affinity of the zinc for the oxygen already combined with hydrogen in 

 the water that is exerted in producing the electric current (919.): and when the 

 affinities are so increased, the view I am supporting leads to the conclusion, that 

 bodies which resisted in the preceding experiments would then be decomposed, be- 

 cause of the increased difference between their affinities and the acting affinities thus 

 exalted. This expectation was fully confirmed in the following manner. 



906. A little nitric acid was added to the liquid in the vessel v, so as to make a 

 mixture which I shall call diluted nitro-sulphuric acid. On repeating the experi- 

 ments with this mixture, all the substances before decomposed again gave way, and 

 much more readily. But besides that, many which before resisted electrolyzation 

 now yielded up their elements. Thus, solution of sulphate of soda, acted upon in the 

 interstices of litmus and turmeric paper, yielded acid at the a?iode and alkali at the 

 cathode; solution of muriatic acid tinged by indigo yielded chlorine at the anode and 

 hydrogen at the cathode ; solution of nitrate of silver yielded silver at the cathode. 

 Again, fused nitre and the fused iodide and chloride of lead were decomposable by 

 the current of this single pair of plates though they were not by the former (903.). 



907. A solution of acetate of lead was apparently not decomposed by this pair, nor 

 did water acidulated by sulphuric acid seem at first to give way (973.). 



908. The increase of intensity or power of the current produced by a simple voltaic 

 circle, with the increase of the force of the chemical action ,at the exciting place, is 

 here sufficiently evident. But in order to place it in a clearer point of view, and to 

 show that the decomposing effect was not at all dependent, in the latter cases, upon 

 the mere capability of evolving more electricity, experiments were made in which the 

 quantity evolved could be increased without variation in the intensity of the exciting 

 cause. Thus the experiments in which dilute sulphuric acid was used (899.) were 

 repeated, using large plates of zinc and platina in the acid ; but still those bodies 

 which resisted decomposition before, resisted it also under these new circumstances. 

 Then again, where nitro-sulphuric acid was used (906.), mere wires of platina and 

 zinc were immersed in the exciting acid ; yet, notwithstanding this change, those 



3 k2 



