Heating Effects of Electricity and Magnetism. 65 



affected, the voltaic arc was taken, first between silver and then be- 

 tween iron terminals ; in the first case, a brilliant green-coloured 

 flame was produced, and in the second, a reddish scintillation or spur- 

 fire effect, just as in the ordinary combustion of the metals. 



So with the discharge of Franklinic electricity between the same 

 two metals, a strip of silvered leather gave the bright green discharge, 

 while a chain of iron gave the spur-fire effect. 



The known transport of particles of the terminals from one pole 

 to the other, — the different effects of different intervening media on 

 induction, as shewn in Faraday's experiments. — the polar tension of 

 such media, &c, were instances of the train of molecular changes 

 consequent upon electrical action. 



Hitherto the polarity of the gaseous medium existing between 

 the metallic or conducting terminals of the electrical circuit was only 

 known as a physical polarity, and not shewn to have an analogous 

 chemical character with that existing in electrolytes anterior to elec- 

 trolysis ; but Mr Grove stated that in a recent communication to 

 the Royal Society he had shewn that mixtures of gases having oppo- 

 site electrical or chemical relations, such as oxygen and hydrogen, or 

 compound gases such as carbonic oxide, were electro-chemically 

 polarized, or had their electro-negative and electro-positive elements 

 thrown in opposite directions : thus, if a silvered plate be made 

 positive in such gases it is oxidised, if negative the dark spot of oxide 

 is reduced ; and an experiment was shewn in which such a plate was 

 thus oxidised and the spot reduced in gaseous media. 



Here, as in the other experiments, was an effect on the terminals, 

 and an effect of polarization of the intermedium. In the experi- 

 ments hitherto shewn, solid terminals were used; it became impor- 

 tant to examine what would be the effect of liquid terminals, for in- 

 stance water ; the spark or disruptive discharge of Franklinic elec- 

 tricity was readily obtained from its surface, but hitherto no voltaic 

 battery had been found to shew a discharge at any sensible distance 

 from the surface of water. 



Mr Gassiot had procured to be constructed 500 cells of the nitrk 

 acid battery, the combination discovered in 1839 by Mr Grove, and 

 first shewn at this Institution in the year 1840. The cells of this 

 battery were all well insulated by glass stems, and as regards inten- 

 sity of action it was probably far the most powerful ever seen. Mr 

 Gassiot had kindly lent this apparatus for the illustratiou of this 

 evening's discourse, and by its aid Mr Grove was able to shew an 

 experiment which he had first made when experimenting with Mr 

 Gassiot some time ago, and which produced the effect he had long 

 sought for, viz., a quantitative or voltaic discharge at a sensible dis- 

 tance from the surface of water. The experiment was made as fol- 

 lows : — a platinum plate forming the anode of the battery was im- 

 mersed in a capsule of distilled water, the temperature of which was 

 raised. A cathode or negative terminal of platinum wire was now 



VOL. LIII. NO. CV.— JULY 1852. E 



