442 Dr Davy on Atmospheric Electricity. 



instances, the precipitation of iodine was always copious and ra- 

 pid, and almost invariably on both the platina wires — sometimes 

 in greatest abundance on that of the inferior conductor, but oc- 

 casionally on the superior ; — even when the platina wires were 

 placed rather more than half an inch asunder, the results were 

 decisive. In these instances it may be inferred that the precipi- 

 tation on the two wires was not simultaneous but in succession, 

 in consequence of the passing clouds, or portions of air in motion, 

 being in different electrical states, — and, as might be expected, 

 in accordance with this, at no time when the wires were under 

 observation was there any indication contrary to this inference. 

 It may be right to mention, that in these trials with the solution 

 of iodide of potassium and starch, the platina wires were cleaned 

 as often as was required, on account of iodine precipitated and 

 adhering to them ; and that the gelatinous solution itself was 

 often changed, which was necessary both owing to its tendency 

 to spontaneous decomposition, and to the iodine precipitated 

 electro-chemically, in part becoming diffused through it. 



Other experiments which I have made on the electro-chemi- 

 cal agency of atmospheric electricity, have been far less satisfac- 

 tory. Using Volta's eudiometer, filled with a strong solution of 

 common salt, no indications could be obtained of the decomposi- 

 tion of water, although the platina wires of the eudiometer-tube 

 connected with the conductors were within one- tenth of an inch of 

 each other, and though the experiment was more than once made 

 when it was thundering. 



The only result obtained clearly shewing the decomposition 

 of water, was in an experiment in which fine sewing needles, 

 coated with sealing-wax, excepting at their points, were substi- 

 tuted for the eudiometer. On one occasion, using this appara- 

 tus with a strong solution of salt, the point of the needle commu- 

 nicating with the inferior conductor was oxidated, whilst the 

 other point communicating with the superior remained bright, 

 and round the latter very minute bubbles of gas were collected. 



