Surface Reactions1

Abstract

M. FRANCIS AND F. P. BURT.—Sorption of ammonia by glass. The quantities of ammonia taken up by a known surface of glass under constant temperature and pressure conditions, and the rates of sorption, have been measured over a temperature range of 0° to 200° C. and a pressure range of 100 mm. to one atmosphere. The experimental attainment of equilibrium proved impossible, but limiting values were assessed by a process of extrapolation. Though complete desiccation of glass is impracticable, it is possible to maintain it indefinitely in such a condition that its behaviour towards ammonia can be closely recovered. The shape of the sorption curve depends on the dryness of the sorbent. The sorption process can be divided into two parts represented by straight lines when log sorption rate is plotted against log time. The slope of both lines is independent of pressure and varies only slightly with temperature, and their point of intersection corresponds, in all cases, to 50 per cent. sorption. By a suitable choice of co-ordinates the complete sorption process can be represented as a single-valued continuous function of temperature, pressure, and time. As regards temperature variation, this is only approximately true. At 50 per cent. sorption, the rate of sorption is nearly proportional to the pressure at constant temperature, and is doubled for every 20° C. rise in temperature at constant pressure At constant temperature, log sorption, in the limit, wa found to be a linear function of log preaure between 0.5 and 1 atmosphere. At lower pressures a departure from linearity was observed. At constant pressure, sorption, in the limit, was found to be inversely proportional to the absolute temperature.