Forces of some Metallic Alloys in Contact with Copper. 47 



The mean value, if the last number be excluded, =1*06; and 

 the deviations from the mean, which at the most amount to only 

 6 per cent., may be attributed to errors of observation. The 

 last quotient may reasonably be looked upon as not comparable 

 with the rest. The combination copper and 32 bismuth 3 anti- 

 mony, in consequence of its great electromotive force, produces 

 in the cylinders of the air-thermometer considerable variations 

 of temperature on the reversal of the current ; and therefore it 

 is possible that the equations employed in the calculation of a, 

 having been deduced on the hypothesis that the temperature- 

 variations in the cylinders are only moderate, furnish for this 

 combination a value of a. which is not comparable with those for 

 the rest of the combinations. This supposition is confirmed by 

 the circumstance that the quotients appear to increase with the 

 electromotive force. Hence we believe we are justified in as- 

 suming that the ratio between the thermoelectric and the electro- 

 motive force of the alloys investigated is constant and equal to the 

 ratio for the iron-copper and copper-bismuth combinations. 



Lastly, let us mention as another result of this investigation 

 the remarkable constant diminution of the electromotive and 

 thermoelectric forces which was observed in the bismuth-tin 

 alloys. Of the pure metals, bismuth seems also to undergo 

 such a change. Taking into consideration the known fact that 

 the thermoelectrical condition of solid conductors is extremely 

 sensitive to molecular changes (for example, slight impurities or 

 a relative displacement of the molecules by mechanical treatment, 

 as tension, torsion, pressure, &c.*), it seems very probable that 

 the phenomenon in question is connected with some molecular 

 alteration. By rapid solidification in the casting-mould free 

 crystallization of the alloy is prevented, and a state of tension is 

 produced, from which the molecules strive to free themselves. 

 Simultaneously, chemical changes may take place ; either the 

 constituents of the alloy may enter partially into chemical com- 

 bination with one another, or combinations that were formed in 

 the casting may again fall asunder. 



Similar molecular changes have been previously observed in 

 some bodies. It is known, for instance, that the freezing-point 

 of an ordinary thermometer rises a little in the course of time 

 in consequence of the diminution in volume of its bulb. A 

 similar phenomenon was observed by M. Edlund in 1857, when 

 readjusting three gauged measures of the Swedish Kanne. The 



* Thomson, Phil. Trans. 1856, p. 711- Magnus, Pogg. Ann. vol. 

 lxxxviii. p. 469. Matthiessen found the thermoelectric force in bismuth 

 and antimony very unequal, according as these metals were investigated 

 after casting or in the state of compressed wires (Pogg. Ann. vol. ciii. 

 p. 412). 



