We begin by comparing Sulphur and Phosphorus. In their elementary state they have in common the fact that any chemical change is bound up with an increase in their weight. In this state both are combustible. Apart from this similarity, there is a great difference between them, as the way of storing them illustrates. For while elementary sulphur needs only an ordinary container, phosphorus has to be kept under cover of water in order to prevent the atmospheric oxygen from touching it. The reason is that the combustible state is natural for sulphur, but not for phosphorus, the latter’s natural state being the oxidized one. This different relationship of sulphur and phosphorus to the oxidizable (reduced) and the oxidized state manifests itself in all their chemical reactions.