It is the grammatical metaphor afforded by chemical symbolism that enables the systematic expansion of the semantics of the field of chemistry, most explicitly in terms of quantified composition. Cf. Halliday & Matthiessen (1999: 288-9):
It is the fact that metaphor multiplies meanings within the semantic system that opens up the possibility of metaphorical chains, with one congruent starting-point and another highly metaphorical end-point (A"' stands for A" stands for A' stands for A; e.g. 'engine failure* stands for 'the failing of an engine' stands for 'an engine failed'). The semantic system is being expanded along the dimension of the metaphorical token-value relation; but the expansion is still within the semantic system itself.
NaCl stands for sodium chloride stands for salt. (Thing+Thing stands for Classifier^Thing stands for Thing.)
