E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
This name, which means beautiful black, was originally given to the Æthiops mineral, or black sulphuret of mercury. It was afterwards applied in joke by Sir Theodore Mayerne to the chloride of mercury, in honour of a favourite negro servant whom he employed to prepare it. As calomel is a white powder, the name is merely a jocular misnomer.Medical Dictionary.