Lecture Xxiii.

Of Mercury.

Mercury is the most fusible of all the metals, not becoming solid but in 40 deg. below 0 in Fahrenheit's thermometer. It is then malleable. It is heavier than any other metal except gold or platina. It is volatile in a temperature much lower than that of boiling water, and in vacuo in the common temperature of the atmosphere; and at six hundred it boils.

In a degree of heat in which it would rise easily in vapour, mercury imbibes pure air, and becomes a red calx, called precipitate per se. At a greater degree of heat it parts with that air, and is running mercury again.

Mercury is not perceptibly altered by exposure to the air.

Mercury is acted upon by the vitriolic acid when hot. In this process vitriolic acid air is procured, and the mercury is converted into a white substance, which being dipped in water becomes yellow, called turbith mineral, one third heavier than the mercury from which it was made. By heat this substance parts with its pure air, and becomes running mercury; but if the process be made in a clean earthen vessel, there will remain a portion of red calx, which cannot be reduced by any degree of heat, except in contact with some substance containing phlogiston. If this be done with a burning lens, in inflammable air, much of the air will be absorbed.

Mercury is dissolved most readily in the nitrous acid, when the purest nitrous air is procured; and there remains a substance which is first yellow, and by continuance red, called red precipitate. In a greater degree of heat the dephlogisticated air will be recovered, and the mercury be revived; but the substance yields nitrous air after it becomes solid, and till it changes from yellow to red.

The precipitates of mercury from acids by means of alkalies possess the property of exploding, when they are exposed to a gradual heat in an iron spoon, after having been triturated with one sixth of their weight of the flowers of sulphur. The residuum consists of a violet-coloured powder, which, by sublimation, is converted into cinnabar.

It seems, therefore, as if the sulphur combined suddenly with the mercury, and expelled the dephlogisticated air in an elastic state.

The marine acid seizes upon mercury dissolved in nitrous acid, and if the acid be dephlogisticated, the precipitate is corrosive sublimate; but with common marine acid, it is called calomel, or mercurius dulcis. This preparation is generally made in the dry way, by triturating equal parts of mercury, common salt and vitriol, and exposing the whole to a moderate heat; when the corrosive sublimate rises, and adheres to the upper part of the glass vessel in which the process is made.

Mercury combines readily with sulphur by trituration, and with it forms a black powder called Ethiops mineral. A more intimate combination of mercury and sulphur is made by means of fire. This is called cinnabar, about one third of which is sulphur. Vermillion is cinnabar reduced to powder.

Mercury readily unites with oil, and with it forms a deep black or blue compound, used in medicine.

It readily combines with most of the metals, and when it is used in a sufficient quantity to make them soft, the mixture is called an amalgam. It combines most readily with gold, silver, lead, tin, bismuth, and zinc. Looking-glasses are covered on the back with an amalgam of mercury and tin.

When mercury is united with lead or other metals, it is rendered less brilliant and less fluid; but agitation in pure air converts the impure metal into a calx, together with much of the mercury, in the form of a black powder.

Heat recovers the pure air, and the mercury, leaving the calx of the impure metal.

Much mercury is found native in a slaty kind of earth, or in masses of clay or stone; but the greatest quantity is found combined with sulphur in native cinnabar.