274 Mr. Henchel on certain Motions produced in Fluid [Oct. 



introducing into a quantity of the pure metal a small quantity 

 of an amalgam of this substance prepared for the purpose, I 

 found my supposition verified ; a most violent negative rotation 

 being immediately produced on completing the circuit, without 

 allowing either wire to touch the mercury. 



24. The presence of this highly electro-positive metal there- 

 fore counteracts the effect of the negative pole, and exalts that 

 of the positive in a degree proportioned to its quantity, till at 

 length it completely overcomes, and even reverses the former 

 effect. As the quantity (in the foregoing experiment) diminished 

 in the alloy by the oxidating action of the positive pole, the 

 mercury, as we have seen, by degrees resumed its original pro- 

 perties. The only effect that may appear obscure is the revul- 

 sion noticed in the direction of the currents when the last por- 

 tion of oxide disappears. It is, in fact, a pretty complicated 

 effect, but capable of easy explanation. The oxidation takes 

 place over the surface of the metal before the last portions of 

 sodium are removed. This is easily proved. We have only to 

 break the circuit altogether, and the crust of oxide will gradually 

 disappear (unless suffered to go too far), being reduced by the 

 sodium beneath it. Were it not then for the crust of oxide, the 

 currents, as has been seen, would be in a positive direction. 

 But the oxide, acting on the stratum of metallic molecules 

 immediately below it, deprives them of their alloy, which it con- 

 verts into alkali, leaving a stratum of pure mercury. Now we 

 have seen that in this, the rotation, in the circumstances of the 

 experiment, would have a negative direction. We have only 

 then to admit that the peculiar action by which the rotations 

 are caused, is confined to the common surface of the mercury 

 and liquid, to have a perfect idea of the mode in which the 

 whole process is carried on. The stratum of pure mercury on 

 the surface is removed by a negative current agreeably with its 

 natural relations, and immediately succeeded by a stratum of the 

 sodiuretted metal from the interior; this, in its turn, is deprived 

 of its sodium by the oxide in contact with it, and is immediately 

 radiated off like its predecessor, and so on till the whole crust 

 of oxide is exhausted or swept off, when the remaining mer- 

 cury, still retaining an excess of sodium, and instantly ren- 

 dered homogeneous, is acted on as an alloy, in the way already 

 described. 



25. That sodium is actually present in the mercury when it 

 has acquired the property of producing currents from the posi- 

 tive pole (which for brevity I will hereafter call the positive 

 property) by contact with the negative wire, may be shown by 

 a very simple and interesting experiment. When the negative 

 wire is detached and the circuit broken, the mercury lies quiet 

 at the bottom of the vessel, with the exception of a slight irre- 

 gular motion on its surface, and now and then a minute gas 



