Vapour pressures of water over saturated solutions of aluminium chloride, aluminium nitrate and aluminium sulphate were determined as a function of temperature. The vapour pressures served to evaluate the water activities, osmotic coefficients and molar enthalpies of vaporization. Molar enthalpies of solution of aluminium chloride hexahydrate, Delta(sol)H(m)(AlCl3 (.) 6H(2)O, T = 295.02 K, m = 0.02084 mol (.) kg(-1)) = -(54.6 +/- 2.1) kJ (.) mol(-1), aluminium nitrate nonahydrate, Delta(sol)H(m)(Al(NO3)(3) (.) 9H(2)O; T = 296.62K, m = 0.01342mol (.) kg(-1)) = (30.7 +/- 1.0)kJ (.) mol(-1) and aluminium sulphate octadecahydrate, Delta(sol)H(m)(Al-2(SO4)(3) (.) 18H(2)O, T = 297.60K, m = 0.00756 mol (.) kg(-1)) = -(46.4 +/- 2.5)kJ (.) mol(-1), were determined calorimetrically.