2. On adding a solution of iodide of potassium to a small quantity of the solution, a bright scarlet precipitate, soluble in excess of iodide of potassium, is produced. 3. If a drop or two of a solution of corrosive sublimate, slightly acidulated with hydrochloric acid, be placed on a sovereign, and the solution and the gold be touched with a piece of zinc or an iron key, the mercury will be deposited as a bright silvery stain on the gold. CALOMEL (_Subchloride_ or _Chloride of Mercury_) is a heavy white powder, which is usually regarded as a safe medicine. Yet, in some peculiar constitutions, it has caused excessive salivation and death, even though only a few grains have been given. In large doses it may be regarded as an irritant poison. It is distinguished from corrosive sublimate by forming a black precipitate with caustic potash and by its insolubility in water. AMMONIO CHLORIDE OF MERCURY (_White Precipitate_).—This substance is a chalky looking powder, containing about eighty per cent. of mercury. It produces vomiting, purging, great pain in the stomach, cramps, and convulsions. Out of fourteen cases, collected by Dr. Taylor, in which from a few to forty grains were taken, only two proved fatal. The remaining preparations of mercury, which in rare instances have been used as poisons, are the _Red Oxide of Mercury_ (red precipitate); the _Red Sulphuret of Mercury_ (cinnabar or vermilion); the _Cyanide of Mercury_; the _Nitrates of Mercury_; and _Turpeth Mineral_. Mercury may be separated from organic admixture by Reinsch’s method. CHAPTER XVIII. PREPARATIONS OF LEAD. Lead, in its metallic state, is not injurious. It is, however, really acted on by acids, exposure to the atmosphere, &c., and converted into carbonate of lead. The chief compounds of this metal which have been found to produce poisonous effects are the acetate, subacetate, and the carbonate. ACETATE OF LEAD (_Sugar of Lead_).—This is sold as a glistening white powder, or in the form of crystalline masses resembling loaf sugar. It is more frequently used as a poison than either of the other compounds. It is very soluble in water and has a sweetish metallic taste. Three or four instances are recorded in which recovery has taken place after an ounce of this substance has been taken in solution.