Electromotive Forces in the Voltaic Cell. 189 
ting the electrodes by a porous cell, zinc cathode showed more 
heat than zine anode, but platinum anode more heat than 
platinum cathode*. He speaks of the local heat developed at 
a tin surface, and shows that it is greater where hydrogen is 
liberated than where tin is dissolved ; and suggests thermal 
observations on four dilute-acid voltameters in one circuit 
with zine and platinum electrodes, arranged according to the 
permutations—zinc-zine, zinc-platinum, platinum-zine, and 
platinum-platinum. Thomson attributes the extra heat at an 
electrode to opposing chemical affinities which have to be 
overcome—a doctrine of “ chemical resistance.”’ 
Bosscha examines and develops all these matters in a series 
of interesting papers published about 1857}. He attributes 
the development of local heat, at a cathode against which 
hydrogen is liberated, to the change of hydrogen from the 
nascent condition to the ordinary one—in other words, to the 
energy of the molecular combination H, H. He finds the 
electromotive forces exhibited by this local generation of heat 
at the surface of different metals in acid to have the following 
yalues in volts :— 
Pt Fe Cu Sn He Zn 
"45 “49 "64 36 12 1:2 
One more memoir I must mention before closing this his- 
torical sketch and discussion thereon, a valuable communication 
by Bouty to the Journal de Physique t, “On Thermoelectric 
Force at Contact of Metals and Liquids, and on the Peltier 
Effect thereat.” He finds the Peltier coefficient at a junction 
of copper with salts of copper eighty times as great as at an 
iron-zine junction, and eleven times as great as bismuth- 
copper. He also measures the metal-liquid thermoelectric 
i.M.F. at different temperatures, and shows that Thomson’s 
thermodynamic formula 
| 7 Tdi 
oilih = aT 
is perfectly true and in agreement with experiment in these 
eases also. He endeavours to see if this Peltier, or, as we 
had better call it for distinction, Joule or Bouty effect, can 
be calculated from the energies of combination. After tabu- 
lating his results alongside of heats of oxidation and heats 
* Showing, I suppose, that while zinc attracts oxygen much and 
hydrogen not at all, platinum attracts hydrogen more than oxygen. 
+ Bosscha, Poge. Ann. vols. ci., ciil., ev., cviil. 
~{ Bouty, Journal de Physique, 1879, viii. p. 341; ix. pp. 229 and 306, 
especially p. 306. 
