REACTIONS OF AMMONIA WITH SOIL II. SORPTION OF NH3 ON ENGLISH SOILS AND ON WYOMING BENTONITE

Sorption isotherms and heats of sorption of NH₃ gas on soils, Wyoming bentonite and silica gel were measured at 27 °C after preliminary drying at 22°-290 °C. Sorption of NMe₃ was also measured on some of the materials. Sorption on soils was not very sensitive to change in drying temperature, even though soil water content was markedly affected. Sorption on bentonite was dependent on drying temperature because this affected ease of lamellar separation. The results suggest that under the conditions employed, NH₃ sorption on the English soils studied is predominantly due to its protonation at pH-dependent charge sites and partly to co-ordination with exchangeable Mg or Ca (but not Na or K). Sorption through mechanisms involving hydrogen bonding is apparently negligible.