676 LECTURE LIV. 



metals, and probably the worst conductor, is zinc ; the next is iron ; then 

 come tin, lead, copper, silver, gold, and platina. (Plate XL. Fig. 553 . . 555.) 



In the same manner as a wire charged with positive electricity causes an 

 extrication of oxygen gas, so thesiipply of electricity through the more con- 

 ducting metal promotes the oxidation of the zinc of a galvanic battery ; and 

 the eftect of this circulation may be readily exhibited, by fixing a wire of zinc, 

 and another of silver or platina, in an acid, while one end of each isloos^, and 

 may be brought together or separated at pleasure: for at the moment that the 

 contact takes place, a stream of bubbles rising from the platina, and a white 

 cloud of oxid falling from the zinc, indicate both the circulation of the fluid 

 and the increase of the chemical action. But when, on the other hand, a 

 plate of zinc is made negative by the action of an acid on the greater part of 

 its surface, a detached drop of water has less cfl^iect on it, than in the natural 

 state: while a plate of iron, which touches the zinc, and forms a part of the 

 circle with it, is very readily oxidated at a distant point: such a plate must 

 therefore be considered, with regard to this eftect, as being made positive by 

 the electricity which it receives from the acid or the water; unless something- 

 like a compensation be supposed to take place, from the effects of 

 induced electricity. Instead of the extrication of. hydrogen, the same 

 causes will sometimes occasion a deposition of a metal which has been dis- 

 solved, will prevent the solution of a metal which would otherwise have been 

 corroded, or produce some effects which appear to indicate the presence of an 

 alkali, either volatile or fixed. All these operations may, however, be very 

 much impeded by the interposition of any considerable length of water, or of 

 any other imperfect conductor. (Plate XL. Fig. 556.) 



It is obvious, that since the current of electricity, produced by a 

 galvanic circle, facilitates those actions from which its powers are derived, the 

 effect of a double series must be more than twice as great as that of a single 

 one: and hence arises the activity of the pile of Volta, the discovery of which 

 forms the most important era in the history of this department of natural 

 knowledge. The intensity of the electrical charge, and the chemical and 

 physiological eft'ects of a pile or battery, seem to depend principally on the 

 number of alternations of substances; the light and heat more on the joint mag- 

 nitude of the surfaces employed. In common electricity, the greatest heat 



