247 



the brightness remaining on the north polar regions is not uniform, 

 but is tinged with large dusky spaces, of a cloudy atmospheric, ap- 

 pearance. From which, and the fore-mentioned changes of colour 

 at the polar regions, added to the changes he has formerly observed 

 in the belts, we have, he thinks, sufficient reason to infer the exist- 

 ence of a Saturnian atmosphere. 



The Bakerian Lecture, on some chemical Agencies of Electricity. By 

 Humphry Davy, Esq. F.R.S. M.R.I.A. Read November 20, 1806. 

 [Phil. Trans. 1807,^. 1.] 



The chemical effects produced by electricity have, Mr. Davy says, 

 long been objects of attention ; but the novelty of the phenomena, 

 their want of analogy to known facts, and the apparent discordance 

 of some of the results, involved the inquiry in obscurity. 



It was very early observed, that acid and alkaline matter appeared 

 in water acted upon by a current of electricity ; but Mr. Davy soon 

 found that the muriatic acid came from the animal or vegetable mat- 

 ters employed to connect the two portions of water ; for when the 

 same cotton was repeatedly used, it ceased to be evolved. The soda, 

 in like manner, was found to proceed from the corrosion of the glass 

 tube, as it did not appear in water electrified in an agate cup. 



To be more certain of this effect, some distilled water was elec- 

 trified in two agate cups, by the current from 150 four-inch plates, 

 the communication between the cups being formed by moistened 

 amianthus. In the first experiment soda was produced in the nega- 

 tive cup, but the quantity was much less than when glass tubes were 

 used ; and on repeating the experiment, its quantity decreased, so 

 that in the fourth experiment the presence of soda was scarcely per- 

 ceptible, in the residual water. The water in the other tube was sour, 

 and appeared to contain nitrous acid, with excess of nitrous gas. As 

 similar effects were produced by electrifying water in small gold 

 cones, Mr. Davy suspected that some minute portion of saline matter 

 had been carried over during the distillation of the water ; notwith- 

 standing it did not affect nitrate of silver, or muriate of barytes. And 

 on evaporating a quantity of it in a silver vessel by a heat not ex- 

 ceeding 140 Fahrenheit, a small residuum was actually left, which 

 appeared to be a mixture of nitrate of soda with nitrate of lead. A 

 portion of this residuum being added to water electrified in the usual 

 manner, and which had attained the maximum of its effect upon tur- 

 meric paper, considerably increased those effects. 



Water slowly distilled, being electrified either in gold cones or 

 agate cups, did not evolve any fixed alkaline matter, though it ex- 

 hibited signs of ammonia ; but in tubes of wax, both soda and potash 

 were evolved, and the acid matter in the positive cup was a mixture 

 of sulphuric and muriatic acids. In a tube of resin the alkali was 

 principally potash. In cups of Carrara marble, primitive marble from 

 Donegal, argillaceous schist from Cornwall, serpentine from the Lizard, 

 and grauwacke from North Wales, soda was uniformly evolved. 



