Until now the determination of the content fo coluble sulphate was - together with other measurements such as pH, shrinkage temperature, and ammonia content - an indication of the degree of degradation of old leather objects in need of conservaiton. Such information might also indicate the resistance against deterioration of newly made commercial leather for conservation purposes. Analysis of sulphur content of new and old leather in different forms, has shown that a considerable cmount of sulphur present in the leather appeared to be bound to the fibres. The consequences arising from this conclusion will be examined in the second part of this project, which will include methods of artificial ageing and a comparison of the durability of commercial bookbinding leathers. -- CAL