In the novel The Murder at the Vicarage, Mr Cherubim is the chemist in St. Mary Mead. Late in the story after Mr Hawes was found unconscious, an empty cachet of sleeping powder was found next to him. The cachet had Mr Cherubim's name on it--presumably he had sold the powder to Hawes.
In adaptations[]
In the 1986 BBC adaptation of the novel The Murder at the Vicarage, the label on the cachet has different details: W. Badger, dispensing chemist in St. Mary Mead. Presumably the Mr Badger the chemist in The Body in the Library.