Electrolytic Intensity for Sulphate of Soda. 275 



intensity enough to decompose the water in the vessel B; for 

 though left for fourteen days, during the whole of which time 

 the current was found to be passing, still not the slightest ap- 

 pearance of gas appeared on the phites P^ P^', nor any other 

 signs of the water having suffered decomposition. 



975. Sulphate of soda in solution was then experimented 

 with, for the purpose of ascertaining with respect to it, whether 

 a certain electrolytic intensity was also required for its de- 

 composition in this state, in analogy with the result established 

 with regard to water (974.). The apparatus was arranged 

 as in fig. 13. ; P and Z are the platina and zinc plates dipping 

 into a solution of common salt; a and b are platina plates 

 connected by wires of platina (except in the galvanometer g) 

 with P and Z ; c is a connecting wire of platina, the ends of 

 which can be made to rest either on the plates a, b, or on 

 the papers moistened in solutions which are placed upon 

 them ; so that the passage of the current without decomposi- 

 tion, or with one or two decompositions, was under ready 

 command, as far as arrangement was concerned. In order to 

 change the anodes and cathodes at the places of decomposition, 

 the form of apparatus fig. 14. was occasionally adopted. 

 Here only one platina plate, c, was used ; both pieces of paper 

 on which decomposition was to be effected were placed upon 

 it, the wires from P and Z resting upon these pieces of paper, 

 or upon the plate c, according as the current with or without 

 decomposition of the solutions was required. 



976. On placing solution of iodide of potassium in paper 

 at one of the decomposing localities, and solution of sulphate 

 of soda at the other, so that the electric current should pass 

 through both at once, the solution of iodide was slowly 

 decomposed, yielding iodine at the anode and alkali at the 

 cathode; but the solution of sulphate of soda exhibited no signs 

 of decomposition, neither acid nor alkali being evolved from 

 it. On placing the wires so that the iodide alone was subject 

 to the action of the current (900.), it was quickly and power- 

 fully decomposed ; but on arranging them so that the sul- 

 phate of soda alone was subject to action, it still refused to 

 yield up its elements. Finally, the apparatus was so arranged, 

 under a wet bell-glass, that it could be left for twelve hours, 

 the current passing during the whole time through a solu- 

 tion of sulphate of soda, retained in its place by only two 

 thicknesses of bibulous litmus and turmeric paper. At the 

 end of that time it was ascertained by the decomposition of 

 iodide of potassium at the second place of action, that the 

 current was passing and had ])assed for the twelve hours, and 



'2. N 2 



