Part 9 (1/2)

LECTURE XXII

_Of Silver_

Silver is the whitest of all the old; the thinnest leaves of it being one third thicker than those of gold It is not calcined in the heat of a co burning lens

Sulphureous fue it black The nitrous acid dissolves it, and will hold ht of it in solution When fully saturated, this solution deposits crystals, which are called _lunar nitre_, or _nitre of silver_ When these crystals are melted, and the water they contain driven off, a black substance, called _lapis infernalis_, or _lunar caustic_, is for heat will decoh the nitrous acid dissolves silver the most readily, the marine acid will deprive the nitrous of it, and form a substance called _luna cornea_, because, when it isrese _horn_ From this luna cornea the purest silver may be obtained The vitriolic acid will likewise deprive the nitrous of the silver contained in it, and form a white powder, not easily soluble in water

A ful process: the silver must first be dissolved in pale nitrous acid, then precipitated by lime-water, dried, and exposed to the air three days It must then be washed in caustic volatile alkali, after which the fluid must be decanted, and the black powder left to dry in the air The slightest friction will cause this powder to ful upon it will produce this effect; so that it ought to be reatest caution

Most of the metals precipitate silver That by mercury may be made to assume the form of a tree, called _arbor Dianae_

Silver is found native in Peru; and the ores frequently contain sulphur, or arsenic, or both

_Of Platina_

Platina is a old mines of Mexico, where it is found in s the size of a pea, est fire will not h it willlens, or a blow-pipe supplied with dephlogisticated air

Pure platina is the heaviest body in nature, its specific gravity exceeding twenty-two It is very old or silver, and has the property of welding in common with iron This metal is not affected by exposure to the air, or by any sih concentrated and hot; but it is dissolved by dephlogisticated ia, in which a little nitrous air is procured The solution is brown, and when diluted yellow

This liquor is very corrosive, and tinges animal substances of a blackish brown colour Platina is precipitated froold is by martial vitriol Iron is precipitated from this solution by the Prussian alkali Also most of the metals precipitate platina, but not in its metallic state

arsenic facilitates the solution of platina; and by etable alkali, and then reducing the mass to a powder, itheat will dissipate the arsenic and the alkali, leaving the platina in the shape required, not fusible by any heat in a coold or silver, and it resists the action ofit less ductile, and even brittle, according to the proportion of the platina With copper it forms a compound which takes a beautiful polish, not liable to tarnish, and is therefore used with advantage fortelescopes It unites easily with tin, and also with bismuth, antimony, and zinc

LECTURE XXIII

_Of Mercury_

Mercury is thesolid but in 40 below 0 in Fahrenheit's thermometer It is then old or platina It is volatile in a te water, and in vacuo in the common temperature of the atree of heat in which it would rise easily in vapour, mercury imbibes pure air, and becoreater degree of heat it parts with that air, and is running ain

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 thedipped 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 beco 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 soiston 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 becoes from yellow to red

The precipitates of mercury fro, 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 coisticated air in an elastic state