The adsorption of hydrogen cyanide and of carbon dioxide at low pressures by activated charcoals

These experiments were carried out, partly because of their own intrinsic interest, but chiefly as a preliminary to work on the simultaneous adsorption by charcoal of two or more vapours. Although for this reason the work here recorded was not pushed very far, it has nevertheless led to results of interest. The technique used, involving the measurement of pressure by the Pirani gauge, was essentially that already described in connection with the sorption of carbon tetrachloride, except that the quantities of carbon dioxide adsorbed at these low pressures, being too small to weigh directly, were calculated from the pressure readings and the volume and temperature of the apparatus. This and other details will be described later. The working temperature throughout was 25° C., unless otherwise stated, and the charcoals in every case were graded by 10 to 12 mesh sieves, initially degassed at 100° to 110° C. down to 10-4 mm. of mercury, and then, after weighing, evacuated to “zero” pressure at 25° before admitting gas. The charcoals used with HCN were A, H, K, and L. Experiments on the same four charcoals were done with CO2 and, in addition on charcoals B, C, F previously used in this laboratory, and on two new charcoals N and O. Of these, charcoal N is a material of bulk density 0·436, manufactured in Czechoslovakia by zinc chloride activation from almond shells. Charcoal O, of Dutch origin, and of which the ash contains a fair quantity of zinc, is probably made from a soft wood by zinc chloride activation. Its bulk density is 0·31.