Mass susceptibilities of alkali sulphates and alums

Abstract

An investigation of the properties of the alums has shown (i) The existence of lithium alum. (2) That the waters of crystallisation are attached in groups of three. (3) That the anhydrous double sulphates are insoluble. The magnetic properties of the alums together with those of the hydrated double salts indicate that each group of three molecules of water make equivalent contributions to the molecular susceptibility and therefore must be attached by a similar type of link. Whilst the magnetic properties of the alkali sulphates show that the ions have a quasi independent existence in the crystal, those of the alums suggest that a complex ion formation prevails. It seems probable that the alkali ions are linked to the tervalent ions and three of the sulphate groups by means of the water molecules so that the formula could be written (R'2 R'2' (SO4)3 24H2O)..SO4. The insolubility of the anhydrous double salts together with the necessity of heat energy in their formation change in structure takes place, and it is suggested that a chelated compound is formed. Crystals of the compound K2SO4AL2(SO4)3 were prepared and it was apparent that the substitution of place of 18 H2O had no distorting effect on the crystal structure nor did it produce any peculiar magnetic effects. The value of the molecular susceptibility of calculated from these results is in good agreement with the accepted value. The paramagnetism of the chromic and ferric alums was too great to give any evidence of similarity of links connecting the water molecules, but they did confirm the idea that the alums have a complex ion structure.