Irreversible Dehydration in Montmorillonite

In a paper to the Faraday Society (1946), Mering showed that the temperature to which one required to heat montmorillonite to produce irreversible collapse of the c-axis depended on the exchangeable cation. With Na-montmorillonite irreversibility began at about 550°C but with Ca-montmorillonite below 350°C During a study of the liquid phase sorption of pyridine by montmorillonite, the writer obtained evidence that irreversible collapse occurred at 200°C with Li-montmorillonite. The source of montmorillonite was a sample of Wyoming bentonite, which was purified by passing through a Sharples supercentrifuge. The resultant exchange capacity to ammonium acetate at pH 7 was about 90 m.e./100 gms. and the displaced ions chiefly consisted of Na+ and Ca++.