A COMPARATIVE STUDY OF THE DEHYDRATION KINETICS OF SEVERAL HYDRATED SALTS

Abstract

Rates of dehydration under full vacuum, and also as the pressure of water vapor due to the dehydration process was allowed to increase, have been determined for a number of hydrated salts. The dehydration of manganous sulphate tetrahydrate, zinc sulphate heptahydrate, nickel sulphate hexahydrate, and magnesium sulphate heptahydrate has been found to proceed through the formation of amorphous intermediates, the last two of these being very stable. The dehydration of nickel nitrate hexahydrate, magnesium nitrate hexahydrate, and probably of ferrous sulphate heptahydrate and cobalt chloride hexahydrate at very low pressures takes place with the formation of crystalline intermediates. The results obtained are discussed in relation to the dependence of rate of dehydration on water vapor pressure previously reported for copper sulphate pentahydrate and for manganous oxalate dihydrate.