mercuric chloride or mercury (II) chloride, chemical compound, HgCl2, a white powder of colorless rhombohedral crystals, somewhat soluble in water. It is also called bichloride of mercury or corrosive sublimate. It is extremely poisonous. Raw egg white may be given as an antidote, since mercuric chloride reacts with egg albumin to form a nearly insoluble precipitate; medical treatment should be sought immediately. Mercuric chloride is sometimes used in dilute solution as an antiseptic for inanimate objects and as a fungicide. It is also used in preparing other mercury compounds; it reacts with mercury metal to form mercurous chloride. Mercuric chloride is prepared by reacting mercury with chlorine gas or by subliming a mixture of mercuric sulfate and sodium chloride (common salt).