156 Royal Society : — 



than those of the electrolyte : the movements of the liquid are hest 

 observed by means of charcoal or asphaltum (5), and those of the 

 mercury by the aid of a few parallel scratches upon the under sur- 

 face of the watch-glass. 



29. The directions of flow of the metal and liquid are intimately de- 

 pendent upon each other, for in every instance the metal moves in an 

 opposite direction to the electrolyte (see also 22) ; and in those cases 

 where two opposite flows of the liquid towards the centre of the vessel 

 occur (as with a solution of sulphate of potash), the globule of 

 mercury is elongated at both ends into a pointed shape, and its two 

 ends point toward the two electrodes, its largest diameter being 

 directly under the point of meeting of the flows of the solution, and 

 its acutest apex under the strongest flow. The relation between the 

 metal and liquid is apparently of a dual or polar character, the move- 

 ments of the two bodies being always opposite and equal. This 

 mutual dependence of the motions explains the necessity of both the 

 substances being in a liquid state (7). 



30. With regard to the direction of the flows, there are three 

 cases to be distinguished: — 1st. The movements obtained by im- 

 mersing the negative wire in the metal and the positive one in the 

 electrolyte. 2nd. Those obtained whilst the positive wire is in the 

 globule and the negative one in the electrolyte. 3rd. Those pro- 

 duced by immersing both the wires in the supernatant liquid with 

 the globule between them. 



31. Upwards of 150 different liquids, including organic and in- 

 organic acids, alkalies, salts of alkalies, earths and heavy metals, also 

 organic salts, were examined by the first of these methods, and in 

 almost every instance the flow of the supernatant liquid was positive, 

 the clearest exception being with a solution of persulphate of iron. 

 With concentrated sulphuric acid the motion (if any) was very feeble, 

 but with diluted acid of various degrees of dilution it was strongly 

 positive. The flow of the liquid declined quickly with solutions 

 which contained an alkali-metal, apparently in consequence of the 

 mercury becoming less mobile (?) by absorption of that metal ; 

 but with dilute acids it continued a long time ; with very dilute nitric 

 acid, in one experiment the movement was sustained with scarcely 

 any diminution during 2\ hours ; and with dilute sulphuric acid, 

 in a second experiment it continued 6J hours, and did not then 

 appear to slacken : the battery employed in this experiment con- 

 sisted of ten small Smee's elements. A globule of strong sul- 

 phuric acid was placed upon a surface of mercury, the latter 

 connected with the negative pole, and the end of the positive 

 wire dipped into the acid ; much gas was evolved from the anode, and 

 the liquid was not repelled on making contact, but collected in a 

 heap around the wire ; — a globule of solution of caustic potash 

 similarly treated exhibited repulsion on making contact. It is 

 evident from these uniform results that the direction of flow obtained 

 by immersing the positive wire in the electrolyte and the negative 

 one in the mercury is almost uniformly positive. 



32. The movements obtained by this method are not produced by 



