calomel (n.)youdaoicibaDictYouDict[calomel 词源字典]
old name for mercurous chloride, 1670s, from French calomel, supposedly (Littré) from Greek kalos "fair" (see Callisto) + melas "black;" but as the powder is yellowish-white this seems difficult. "It is perhaps of significance that the salt is blackened by ammonia and alkalis" [Flood].[calomel etymology, calomel origin, 英语词源]