Solid Phase Determinations in the System Aluminium Sulphate/Sulphuric Acid/Water using Tracer Technique

Abstract

IN the system aluminium sulphate/sulphuric acid/water, the solid phase in the range 50–60 per cent sulphuric acid has been reported to be either Al₂(SO₄)₃.9H₂O ^1,2 or Al₂(SO₄)₃.10H₂O³ at temperatures between 20° and 60°, the composition of this solid being deduced by the Schreinemakers⁴ method of tie-line convergence. However, in view of (a) the high molecular weight of aluminium sulphate compared with sulphuric acid and water, (b) the relative position in the equilateral triangle of the solubility curve, (c) inaccuracy in the position of the solution and moist solid points owing to the well-known difficulty of determining sulphuric acid in presence of aluminium sulphate, the published tie-lines show equally good convergence at points representing the 8, 9 or 10 hydrates or the 1 : 1 acid sulphate with eleven to thirteen molecules of water of crystallization.