ELASTIC PROPERTIES OF THE DITHIONATES NA2S2O6-CENTER-DOT-2H2O, K2S2O6, RB2S2O6, CAS2O6-CENTER-DOT-4H2O AND SRS2O6-CENTER-DOT-4H2O

Single crystals of the title compounds having optical duality and dime nsions of several cm were grown from aqueous solutions. The elastic an d thermoelastic constants were determined from ultrasonic resonance fr equencies of thick plates. The true point symmetry of K2S2O6 and Rb2S2 O6, which is screened by a hexagonal hypermorphy, could be clearly rev ealed to be trigonal (32) by the existence of the elastic constant c(1 4). In the case of CaS2O6.4 H2O and SrS2O6.4 H2O the constant c(14) of the specimens appeared too small to confirm the trigonal symmetry gro up required from electrooptic and non-linear optic effects unambiguous ly.