163 Royal Society :— 



one method have not that property with the other method, except 

 hypophosphite and diphosphate of soda. The explanation suggested 

 (34), of the cause of the true movements of methods 1 and 2 does 

 not appear applicable to these phenomena of reversion. 



43. Herschel has shown that with pure mercury in solutions of 

 alkalies or of sulphate of soda (vide Gmelin's 'Handbook,' i. 490,492), 

 if a little alkali-metal be introduced into the globule by connecting 

 the latter for a few moments with the negative wire (the other wire 

 being in the solution), a positive flow occurs on placing both the 

 wires in the electrolyte with the mercury between them, and con- 

 tinues until all the alkali-metal is redissolved ; and that similar effects 

 are produced by adding small quantities of an easily oxidizable metal 

 to the mercury — for example, potassium, sodium, barium, zinc, iron, 

 tin, lead, or antimony, in the order given; but not by bismuth, 

 copper, silver, or gold. I have found that zinc added to mercury 

 under a solution of sulphate of potash changed the direction of flow 

 from positive and negative (obtained by method 3) to positive only ; 

 cadmium did the same, but more feebly, and tin still more feebly ; 

 bismuth had no apparent effect, but by using treble the electric 

 power its effect was also similar, antimony also the same ; gold had no 

 apparent effect even with a current from 72 pairs of Smee's elements. 

 No positive flow was obtained by connecting the mercury with the 

 negative wire and the solution with the positive wire for a short time 

 in a liquid consisting of acid and water, and then placing both the 

 wires in the electrolyte. Although there are many liquids (most of 

 those which contain an alkali-metal) in which a temporary positive 

 flow (or increase of positive flow) may be obtained by the 3rd me- 

 thod by first placing the negative wire in the mercury for a short 

 time and then returning it to the electrolyte, there are but few 

 (among which are diphosphate of soda and arseniate of ammonia) 

 in which a temporary negative flow is produced by placing the 

 positive wire in the mercury and then returning it to the solution. 

 It has been constantly observed with the 3rd method, that purity of 

 the mercury is essential to the production of uniform results. From 

 these various facts it appears that the chemical nature of the metallic 

 globule strongly influences the direction of the movements obtained 

 by method 3 ; also that an electro-positive globule produces a 

 positive flow, and an electro -negative substance dissolved in the 

 mercury produces a negative flow. 



44. In some instances of the 3rd method — for example, with solu- 

 tions of chloride of magnesium and nitrate of magnesia (35, Table), 

 even the degree of dilution appears to determine the direction of the 

 motion. No variation in the direction of the movement obtained by 

 either method was observed on varying the strength of the electric 

 current, or on varying either the actual or relative distances of the 

 electrodes from the metallic globule. 



45. The presence of an electro-positive metal in one portion of 

 the surface of the mercury will (by generating a small electric 

 current) sometimes cause rotation of the electrolyte after the battery- 

 wires are removed, especially if the mercury is touched with a pla- 

 tinum wire heneath the surface of the liquid ; this is seen most 



