288 Dr. G. Gore. Relations of Heat to Voltaic and 



and in dilate chloric acid iron alone was thermo-negative, but in 

 contact with tin it was more positive up to 150 F. These cases were 

 observed whilst making experiments to determine the balance points 

 of Table XVII (p. 279), but were not included in that table because 

 they did not yield balances. 



In each of these causeg the electric effect of heat upon the same 

 metal in the same liquid was opposite to its usual thermo-electric one 

 in that liquid. In each case also its effect was to increase, within the 

 limits of a moderate rise of temperature, the strength of the already 

 existing voltaic current. These changes may be explicable by sup- 

 posing that the additional irregularities of electric potential intro- 

 duced by the second metal at its two points of contact with the liquid 

 and original metal altered the electric condition of the subsequently 

 heated metal. The pre-existing voltaic currents also were so feeble 

 that these unusual effects of heat do not appear to have been due to 

 chemical changes of the liquid at the heated electrode ; such changes, 

 and the degrees of polarisation due to them, must also have been 

 small in comparison with those already produced by ordinary chemical 

 corrosion. 



In a separate communication "On some Relations of Chemical 

 Corrosion to Voltaic Currents," " Proc. Roy. Soc.," vol. 36, p. 331, 

 I have examined the amounts of external voltaic current produced by 

 the corrosion of known weights of various metals at atmospheric 

 temperature. 



The general conclusions drawn from the experiments described in 

 the present paper may be found in the " Abstract," " Proc. Roy. Soc.," 

 vol. 36, p. 50. 



The fact that the mere contact of the metal and liquid of a thermo- 

 electric pair is attended by electric polarity, and that either heating 

 the one junction or cooling the other of such a couple produces an 

 electric current, may be regarded as evidence that at all times, whilst 

 no heat or cold is being applied to either of these joinings, the mole- 

 cular actions at the two points of union tend to produce a current, 

 but as these tendencies are opposite in direction and equal in strength, 

 no current occurs. Each of these junctions may also be regarded as 

 a surface of contact previously possessing a tendency to alter in tem- 

 perature, and this view is supported by the discovery of Pouillet, that 

 even when non-corrodible metals touch liquids, a slight change of 

 temperature occurs (" Annal. de Chimie," 1822, pp. 141-162). 



In support of this view, it may be observed that amongst the 

 instances composing the chemico-electric series of Table X are many 

 the currents of which are at the most of doubtful chemical origin. Of 

 these, are the cases in which currents are produced by non-corroded 

 metals, such as platinum, gold, palladium, and silver, in feebly 

 corrosive liquids, including solutions of neutral salts. A suitable 



