In this paper chemical substances are represented as “operands,” and chemical processes as “operators”—thus, φ·x is the substance produced by acting on the substance x by the process φ. When φ, χ, ψ, &c., act independently on x, this is indicated by the notation . When they act one on another to produce a complex operator which acts on x, the notation φ·χ·ψ·x is used. It is shown that in the latter case the commutative law does not apply to operators.