A rhyme we were given at night-school classes for remembering scientific formulae:

Little Jim is dead and gone,
His face we'll see no more,
For what he thought was H20
Was H2SO4 (sulphuric acid)

Jim Carroll
PS and then, of course, there was Little Jim who has "fallen in the water", but that is for people of a certain age who remember 'The Goon Show'.