Mercurius dulcis could also be called Mercurius muriaticum, as it is really the chloride of mercury. But there is another type of mercury chloride, i.e. Mercurius corrosivus. The difference is that in Mercurius corrosivus the mercury is bivalent in HgCl2, whilst in Mercurius dulcis it is monovalent in Hg2Cl2. One might think the latter should be written as HgCl, but it appears that the mercury still makes two connections, even if it is monovalent: Cl-Hg-Hg-Cl, like a short chain. Another name for this compound is calomel, which means beautiful (kalos) black (melos).