Abstract: The expansion of montmorillonite at various relative pressures of ammonia up to saturation was shown to be markedly affected by the kind of ion present on the exchange complex. A 12.3 Å spacing was obtained with Li-, Na-, K-, Mg- and Ca-montmorillonites at low relative pressures. This spacing was maintained up to saturation for the K and Mg systems and apparently represents one layer of ammonia in the interlamellar spaces. For Li-, Na- and Ca-clay, two layers of ammonia were formed at higher relative pressures. In the cases of Cu- and Co-montmorillonite, rational spacings at 12.8 and 15.1 Å respectively were obtained at low relative pressures and were maintained to saturation. The results are interpreted in terms of co-ordination complex formation.
Electrical conductance studies showed exponential increases in conductivity as the relative pressure of ammonia increased. The apparent activation energies showed decreases with increase in relative pressure for all systems except Co- and Mg-clay, which remained rather constant over the pressure range studied. The results indicated that both expansion and electrical conductivity were influenced by the formation of the ammonium ion and by the co-ordinating power of the exchangeable cation.