Full Idea
Neither mercury as a metal nor oxygen as a gas is contained in mercury oxide; it only contains the substance of the elements, just as steam only contains the substance of ice.
Gist of Idea
Elements don't survive in compounds, but the 'substance' of the element does
Source
Dmitri Mendeleev (The Principles of Chemistry [1870], I:23), quoted by Eric R. Scerri - The Periodic Table 04 'Nature'
Book Reference
Scerri,Eric R.: 'The Periodic Table' [OUP 2007], p.115
A Reaction
[1889 edn] Scerri glosses the word 'substance' as meaning essence.
Related Idea
Idea 17392 How can poisonous elements survive in the nutritious compound they compose? [Scerri]