1.1 ,This practice is based on studies relating the rate of deterioration of leathers having known durabilities from long-term storage of samples, to the deterioration experienced by laboratory exposure of specimens to known contents of acid gases in air or oxygen. This is accomplished by measuring the deterioration (reduction in tensile strength) of leather specimens when they are subjected to exposure to a mixture of air, moisture and sulfur dioxide at a given temperature and pressure and for a given exposure time. The loss of tensile strength of the specimens resulting from this exposure is compared to that experienced by a variety of leathers having various tannages and having historically long and short service lifetimes. The initial tensile strength and the degree of loss of tensile strength is related to what service life can be anticipated from a given leather.