Note 28 — Chapter XXIV · COPPER, SILVER, AND GOLD

bis] In Chapter XXII., Note 40, we gave the thermal data for certain of the compounds of copper of the type CuX2; we will now cite certain data for the cuprous compounds of the type CuX, which present an analogy to the corresponding compounds AgX and AuX, some of which were investigated by Thomsen in his classical work, ‘Thermochemische Untersuchungen’ (Vol. iii., 1883). The data are given in the same manner as in the above-mentioned note:

R = Cu Ag Au

R + Cl +33 +29 +6

R + Br +25 +23 0

R + I +16 +14 -6

R + O +41 +6 -?

Thus we see in the first place that gold, which possesses a much smaller affinity than Ag, evolves far less heat than an equivalent amount of copper, giving the same compound, and in the second place that the combination of copper with one atom of oxygen disengages more heat than its combination with one atom of a halogen, whilst with silver the reverse is the case. This is connected with the fact that Cu₂O is more stable under the action of heat than Ag₂O.