274 Upon Caloric as a Cause of Galvanic Currents. 



by heat. The currents produced by fragments of gold, are always 

 feeble, and when copper is also present, the oxidation at the surface 

 makes it almost impossible to distinguish any effect. 



Tin and lead furnish very equivocal results, even when one por- 

 tion of the metal is as cold as ice, and the other heated, nearly to 

 fusion. This is perhaps owing, in a great degree, to oxidation. 

 Zinc and silver must be heated in a coal fire and large bars used in 

 order to obtain currents of sufficient force. The arsenic, employed, 

 was the crude article of the shops; but its indications were sufficient- 

 ly conspicuous when one of the fragments was heated until the white 

 vapor of arsenious acid appeared. 



When dissimilar metals form the thermo-electric circuit, we do 

 not perceive the relation which the elements have towards caloric. 

 Becquerel is of opinion that the forces, as observed by him, bear a 

 direct relation to the radiating power of the combined metals, (Ann. 

 de Chimie &c. 1829,) but, most assuredly, this explanation is not ap- 

 plicable to the combination of portions of the same metal, and it ap- 

 pears obvious, that in such cases, the direction and intensity of the 

 current result from the course which the caloric takes, during its 

 transmission from the hot portion to the cold. 



It appears evident from the results furnished in the foregoing table, 

 that the metals naturally divide themselves into two classes ; in the 

 one (including bismuth, nickel, mercury, iron, gold, zinc, tin and 

 lead) the positive galvanic current moves in opposition to the caloric; 

 in the other, (consisting of silver, copper, platinum, arsenic and an- 

 timony,) these currents coincide. The cause of this difference is by 

 no means apparent, but it is obvious that it must operate with equal 

 force in modifying the currents produced by the contacts of different 

 metals. Pursuing the principles of investigation already described, 

 for elementary combinations, it is easy to determine the influence 

 which caloric exerts upon compound thermo-electric circuits, or 

 those consisting of dissimilar substances. The process consists in 

 connecting each metal with the galvanic muhiplier ; one of them is 

 then to be heated, in order to ensure the direction of the caloric, 

 and in this state, made to touch the other metal which preserves its 

 natural temperature. 



The result invariably proved to be that the caloric, proceeding in 

 one direction, which varies, however, for each combination, either 

 diminishes, destroys or inverts the currents which the same metals 



