The expansion of charcoal on sorption of carbon dioxide

In the examination of certain building materials it has been found that an expansion takes place on absorption of water. This expansion is a movement of the order of strain movements in structural materials and not of the magni­tude expected by the physical chemist in connection with elastic gels. Accom­panying this small expansion of building materials is a fundamental change in physical properties. McBain ('Journal of Physical Chemistry’) showed that the building materials which possess the property of swelling with increased water content are colloidal structures, presumably of the rigid gel type. It therefore appeared desirable to ascertain whether rigid gels in general exhibited this small swelling movement. Graham has shown that palladium expands linearly by 1.6 per cent. when it absorbs hydrogen.