Amounts of adsorption of helium over some zeolites were determined ranging from 77 to 673 K with a temperature‐compensated, differential tensimeter having symmetrical design. The amount of adsorption of helium was determined by measuring an increase in apparent dead space between the sample adsorption cell containing the sample and the reference adsorption cell containing several glass rods on the assumption that the amount adsorbed of helium at 673 K was negligibly small, the temperature of the adsorption cells being changed after each determination. Discussion has been made of the errors caused by the adsorption of helium to the determination of the density of solids when helium is used as the dilatometric fluid, and the determination of the surface areas of solids based upon the adsorption of nitrogen with a conventional volumetric adsorption apparatus.