The short survey concerns the discovery of adsorbents and the measurement of the adsorptivity. In the investigation of adsorption
very sensitive instruments are needed, developed only recently. Two methods, however, are very old: the volumetric and the
gravimetric measurement of the adsorbed amount. In the Bible we find a thorough description of a volumetric adsorption experiment.
The systematic research began in 1773 when Scheele, Fontana and Priestley observed the adsorption of air by charcoal. The
volumetric apparatus of Brunauer, Emmett and Teller set the prototype for many instruments devoted to measure adsorption isotherms.
The first gravimetric adsorption measuring instruments were hygrometers, described by Nicholas of Cues in 1450, Alberti and
Leonardo da Vinci. In 1833 Talabot installed 39 drying balances in a Lyon laboratory for humidity control of raw silk imported
from China. In 1912 Emich described an electronic beam microbalance to investigate adsorption and a coil spring balance. Today
isotherms are measured gravimetrically by means of electro-dynamically compensating microbalances. Also oscillating systems
are being used which allow weighing down to the zeptogram region.
DNA adsorbed very low amount of water at low relative humidities, amount of adsorption increased to 140% at 98% relative humidity
at 25°C. Heat of adsorption was 109 kJ mol-1 H2O for the increase of moisture content from 0 to 1.96%. At higher moisture contents the heat released approached heat of condensation
of water vapour on free liquid surface, 40 kJ mol-1 H2O.
Adsorption equilibria of pure gases and binary gas mixtures can be measured with a new magnetic suspension balance. For this measurement no additional concentration measurement is required, neither for the gas phase nor for the adsorbed phase. The new instrument allows gravimetric adsorption measurements in a wide range of pressure (UHV...50 MPa) and temperature (210 K...570 K) to be performed. The experimental procedure and the instrument set up is fairly easy and can be compared to pure gas adsorption experiments. The new instrument and experimental procedure have been tested by performing coadsorption measurements with CO/H2 mixtures on a commercial 5A zeolite.