146 Galvano-magnetism. 



ment made according to the European plan, with eighty feet of Cop- 

 per wire covered with silk. 



It is well known that of two metals of different susceptibility of ox- 

 idizement, after contact with each other, that will be found positive, 

 which is most oxidizable, and that negative, which is the least at- 

 tractive of oxygen. In this sense copper is said to be negative in re- 

 lation to zinc. It should however be recollected, that since the more 

 oxidizable metal becomes positive by a discharge from the other, 

 during the existence of a galvanic circuit, the metal which is nega- 

 tive in the sense above mentioned, forms the positive pole. Thus, 

 if we constitute a circuit of zinc, moistened paper, and copper, the 

 copper is positive ; and if we connect it with the end of the coil 

 which enters over the needle, and stand so as to look in that direc- 

 tion, the north pole moves to the left. 



Having supphed the bottom of a saucer with a stratum of mercury 

 from my pneumatic cistern, covered by water and paper, a disc of 

 copper was placed over it on the paper. Under these circumstances 

 I was surprized to find that when a wire proceeding from one pole of 

 the multiplier, was held in contact with the copper, and the other 

 wire dipped into the mercury, the same deflection took place as when 

 a similar circuit was made, substituting zinc for mercury, the same 

 wire being in both cases kept in contact with the copper. On sub- 

 stituting successively iron, tin, lead and tin plate, for the copper, the 

 same wire being in contact with the mercury as in the first instance, 

 I found this metal to have the same relation to all of them as zinc. 



Its relation to zinc was found to be feebly of an opposite kind. 



Subsequently, I procured an adequate quantity of pure mercury, 

 by precipitating the protonitrate, by copper. This I found to have 

 a polarity with copper and all the other metals above named, the op- 

 posite of that which the impure metal had with them. The impure 

 metal had the same reladon to it as zinc. Thus we have a conven- 

 ient method of testing the purity of mercury, since a very slight im- 

 purity readers this metal in the circuit negative with copper, unless 

 the impurity be of one of the precious or less oxidizable metals. 

 Possibly we may in this way have the means of testing gold and sil- 

 ver, by amalgamation with mercury. 



Having the keeper, and a weight of about fifiy-six pouuds, sus- 

 pended by a galvanic magnet, of which the coils were in the circuit 

 of a galvanic pair of about a square foot of surface, I attached one 

 pole of my calorimotor, of fifty square feet, to the keeper, and the 



