ELECTROLYTIC INTENSITY FOR SULPHATE OF SODA. — CHLORIDE OP LEAD. 451 



ascertaining with respect to it, whether a certain electrolytic intensity was also re- 

 quired for its decomposition 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 h 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 «, h, or on the papers moistened in solutions which are placed upon them ; so 

 that the passage of the current without decomposition, or with one or two decompo- 

 sitions, 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 appa- 

 ratus 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, ac- 

 cording 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 powerfully decomposed ; but on arranging 

 them so that the sulphate 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 solution of sulphate of soda, retained in its place by only two thicknesses of bibu- 

 lous 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 passed for the twelve hours, and yet no trace of acid or alkali 

 from the sulphate of soda appeared. 



977- From these experiments it may, I think, be concluded, that a solution of sul- 

 phate of soda can conduct a current of electricity, which is unable to decompose the 

 neutral salt present ; that this salt in the state of solution, like water, requires a cer- 

 tain electrolytic intensity for its decomposition ; and that the necessary intensity is 

 much higher for this substance than for the iodide of potassium in a similar state of 

 solution. 



978. I then experimented on bodies rendered decomposable by fusion, and first on 

 chloride of lead. The current was excited by dilute sulphuric acid without any nitric 

 acid between zinc and platina plates, fig. 15., and was then made to traverse a little 

 chloride of lead fused upon glass at a, a paper moistened in solution of iodide of 

 potassium at h, and a galvanometer at g. The metallic terminations at a and h 

 were of platina. Being thus arranged, the decomposition at b and the deflection at g 



