Values are given for the adsorption of sulfuric acid on a vegetable-tanned leather. The measurements were made in aqueous solutions, at concentrations from 0 to about 1.5 molal. Considering the observed adsorption as the sum of two effects - combination of sulfuric acid with the leather, and adsorption due to the surface tension effect. - an expression is developed giving the adsorption as a function of the equilibrium concentration. A similar expression, involving a consdieration of the effect of swelling, is derived. This expression is tested in its application to data, given by Kubelka and Wagner, for the adsorption of hydrochloric acid on collagen.