Note 40 — Chapter XXII · IRON, COBALT, AND NICKEL
George Kamensky translation
The following are the thermo-chemical data (according to Thomsen, and referred to gram weights expressed by the formula, in large calories or thousand units of heat) for the formation of corresponding compounds of Mn, Fe, Co, Ni, and Cu (+ Aq signifies that the reaction proceeds in an excess of water):
R = Mn Fe Co Ni Cu
R + Cl2 + Aq 128 100 95 94 63
R + Br2 + Aq 106 78 73 72 41
R + I2 + Aq 76 48 43 41 32
R + O + H2O 95 68 63 61 38
R + O2 + SO2 + nH2O 193 169 163 163 130
RCl2 + Aq +16 18 18 19 11
These examples show that for analogous reactions the amount of heat evolved in passing from Mn to Fe, Co, Ni, and Cu varies in regular sequences as the atomic weight increases. A similar difference is to be found in other groups and series, and proves that thermo-chemical phenomena are subject to the periodic law.