MERCURY. 315 



cific gravity at 47° above 0, is 13'6. It is volatalized at a red 

 heat, and its vapour rises in small quantities, even at the common 

 temperature of the air. At about 660° Fahrenheit, it boils rapidly 

 and may be purified by distillation. When mercury is violently 

 agitated for a long time in contact with atmospheric air, it becomes 

 converted into a black, insipid, insoluble pdwder or protoxide, 

 which consists of 200 parts of metal and 8 of oxygen. When 

 heated to near its boiling point, it combines slowly with the oxygen 

 of the air, and is converted into a brilliant crimson-coloured scaly 

 mass, which is the red or peroxide of mercury. A careful analysis 

 shows that it contains just double the quantity of oxygen in the 

 protoxide, or 16 parts in every 200. Both the oxides of mercury 

 combine with the acids and constitute salifiable bases. Mercury 

 combines with chlorine in two proportions, constituting the well- 

 known and highly important substances, calomel and corrosive sub- 

 limate. It combines also with sulphur, phosphorus, iodine, and 

 most of the metals forming alloys, which have been called amal- 

 gams. By triturating mercury with unctuous or viscid substances, 

 it is changed partly into protoxide, and partly into very minute 

 globules. 



Mercury is brought to this country in leathern skins or large 

 iron bottles, and when in the original packages it is generally very 

 pure. It is often adulterated by the admixture of other metals, 

 particularly lead, tin, zinc, and bismuth. When any of these are 

 present, the metal has a much duller appearance than it usually 

 presents, and is covered with a grey film ; when a small portion is 

 separated, the globules do not preserve exactly the spherical form, 

 nor unite easily with each other ; and when agitated in a phial, 

 it soils or adheres to the glass. Lead is detected by digesting the 

 sophisticated mercury in nitric acid, and adding sulphuretted 

 hydrogen or an alkaline hydro-sulphuret to the solution, which 

 immediately occasions a copious white precipitate. Bismuth is dis- 

 covered by dropping the nitric solution into a large glass of distilled 

 water, when the subnitrate of bismuth will be precipitated in the 

 form of a white powder. If tin be present, a purple precipitate 

 will be formed on adding a solution of the nitro-muriate of gold. 

 Zinc is detected by exposing the mercury to a strong heat ; the 



