mercurous a of or containing mercury Usage(s) One compound of mercury (calomel, mercurous chloride) is a useful purge. Rosenthal's antidote is sodium formaldehyde sulphoxylate, which changes the poison into less toxic mercurous compounds. Among common drugs administered to make the gall bladder evacuate the bile are calomel (mercurous chloride), rhubarb, mandrake, jalap. Synonym(s) mercuric