280 Mr. Herscheloit certain Motions produced in Fluid [Oct. 



little management, may be preserved tolerably clean of film and 

 air bubbles, when kept in fusion under a boiling solution of 

 sugar, acidulated with phosphoric acid, in which case the same 

 circulation takes place as in the case of mercury, viz. from the 

 negative to the positive pole. When solution of sugar alone 

 however was used, the influence of the tin and lead became 

 sensible, the predominant radiation being from the positive pole; 

 a feeble counter-current being, however, observed from the 

 negative. 



41. The contact of the positive pole, in like manner, commu- 

 nicates peculiar properties to mercury, but less strongly marked, 

 and which appear to depend, in part, on the film of oxide formed 

 on its surface, and partly on an absorption of oxygen by the 

 metal itself; a thing rendered not improbable by the analogy of 

 silver and other metals, which, when fused in contact with air, 

 absorb oxygen without losing their metallic appearance. The 

 facts I have observed are chiefly these : 



42. Equal quantities of mercury were electrified for equal 

 times in two separate capsules, under similar solutions of carbo- 

 nate of soda, one in contact with the negative wire, and the 

 other with the positive. On mixing them together, the mercury 

 was acted on as if pure, and showed no signs of containing 

 sodium. Here, the mercury in contact with the positive pole 

 had acquired a virtue capable of counteracting the effect of a 

 considerable impregnation of sodium, which, had it not been 

 counteracted, could not fail to be violent. 



43. When mercury is kept in contact with the positive pole, 

 the surface contracts a film of oxide of more or less considerable 

 thickness. Now, break not only the contact, but the circuit. 

 The mercury will be quite still ; but the moment it is touched 

 with a clean metallic wire (not electrified), the oxide disappears 

 rapidly at the point of contact, as if absorbed, and the remainder 

 rushes in on all sides to supply its place, producing a system of 

 current in the surface radiating towards the wire. It is not 

 indifferent with what metal the contact is made ; potassium, 

 sodium, barium, tin, and zinc, are those which produce the most 

 violent action, the surface brightening instantly with a kind of 

 flash like the brandishing of melted silver, tin being in this 

 respect superior to zinc. The effect of iron is pretty consider- 

 able, that of copper less so, and of antimony and platina, none 

 at all ; neither had phosphorus any effect. 



44. The effect, therefore, depends on the oxidability and 

 amalgamating property jointly ; and this points out the modus 

 operandi. An amalgamation takes place at the point of contact, 

 and this brings the oxidable metal into chemical contact with the 

 oxide immediately around that point, which is instantly reduced. 

 The motion of the surface is, however, doubtless an electric 

 effect, for when mercury, not recently electrified is touched, 



