Chemical potential of water from measurements of optic axial angle of zeolites

Values of the uncorrected optic axial angle (2H(alpha)) of a crystal of the calcium zeolite stellerite (CaAl(2)Si(7)O(l8) . 7H(2)0) immersed in calcium chloride solutions of known activity of water (a(w)) are directly proportional to log a(w). A general relationship between the chemical potential of water in the crystal and the optic axial angle is obeyed.