4'J2 



liEl'OUT — 1884. 



•f 



Bosscha examines and develops nil these matters in a series of ii\t( •.- 

 cstin<T papers published about 1857.' lie attributes the development .1 

 local heat, at a cathode against which hydro<^en is liberated, to tlie chancji; 

 of hydrogen from the nascent condition to the ordinary one — in oOn ;• 

 words, to the energy of the molecular combination IT, H. Ho finds the 

 electro-motive forces exhibited by this local generation of heat at ili.i 

 surface of different 7uetals in acid to have the following values in volts : - 

 Ft Fo Ca Sn Hg Zn 



•45 '49 -64 -86 1-2 1-2 



One more memoir I must mention before closing this historical sketch 

 and discussion thereoii ; a valuable communication by Bouty to the 

 ' Journal de Physique,' ■^ ' On thermo-electric force at contact of metals and 

 liquids, and on the Peltier effect thei'eat.' He finds the Peltier co- 

 efhcienc at a junction of copper with salts of copper eighty times a-i 

 great as at an iron-zinc junction, and eleven times as great as bismutli- 

 copper. IIo also measures the metal-liquid thermo-electric E.M.P. at 

 different temperatures, and slunvs that Thomson's thormo-dynamic formula 



d T 

 is perfectly true and in agreement with experiment in these cases also. 

 He endeavours to see if this Peltier, or, as we had better call it for dii?- 

 tinction, Joule or Bouty effect can be calculated from the energies of com- 

 bination. After tabulating his results alongside of heats of oxidation and 

 heats of solution, he decides that it is hopeless, and that we must give up 

 trying to establish a relation between these quantities. Chemical action, 

 he coiiclndes, only disturb3 the effect by altering the surfaces, and by 

 developing parasitic heats. They may mask, but they do not product.', 

 the true Bouty ))]ienomenon, which he believes is probably physical. 



The difficulties of making these measurements aro exceedingly great, 

 and, notwithstanding the ingeimity and skill displayed, it seems to me 

 possible that some ei-ror or unexpected source of disturbance may have 

 modified the lesults. So far as I know, they have not yet been repcatcJ, 

 and I can hardly regard the experimental method used as perfectly safe.^ 



7. The result of our survey in regard to the special subject of discussion 

 may be summed up thus : (1) that there is certainly an E.M.F. at the 

 junction of two ditferent substances, or even of the same substance in 

 two different states; and (2) that the total E.M.F. of a circuit is the 

 algebraic sum of all such contact forces at every junction in the circuit. 



I do not know that these two propositions could be passed nem. con., but 

 I believe that, provided they were properly understood, the dissenting 

 minority would be a very small one. It is probable that Professor Exner 

 would be ill the minority, but I am unable to bo sure of anyone else. 



Wo can also make a negative proposition which will corarnand 

 almo!-t universal assent — viz., that if in the above second propositicn, 



' llossdia: Pogf). Ann. vols, ci., o.iii., cv., cviii. 



» l?out.y : Journal de Pliyinqui', 187!), viii. p. :U1 ; ix. p. 220, and p. :W6 ; csp. p. SOi;. 



* I find tliat ii inothrid exactly like that used by Jioiity was siiirgestcd liy Clcr/C 

 Maxwell, Elcmcntarji Mcctricity, p. llC. 



Various observations regarding the E.M.F. of different cells are made in the scric 

 of papers .'itill appearing in the Phil. Ma;]., by Dr. Wright and .Mr. Thompson, ' On 

 the determination of Chemical Aflinity in terms of K.M.F.' 



