Part 10 (1/2)

At a heat far below ignition, the surface, of copper becoe of prismatic colours, the commencement of its calcination; and with more heat a black scale is for heat it reen flame

Copper rusts by exposure to the air; but the partially-calcined surface adheres to the metal, as in the case of lead, and thus preserves it from farther corrosion

Copper dissolved in the vitriolic acid forms crystals of a blot colour, called _blue copperas_ From this solution it is precipitated by iron, which by this means becomes coated with copper The nitrous acid dissolves copper withnitrous air If the solution be distilled, almost all the acid will be retained in the residuum, which is white; but isticated air, and the re of the pure calx of copper The vegetable acids dissolve copper as well as the mineral ones, which makes the use of this erous To prevent this they give it a coat of tin The solution of copper in the vegetable acid is called _verdigris_

Alkalies dissolve copper as well as acids With the volatile alkali a blue liquor is formed, but in some cases it becoe of colour have not yet been examined Both oil and sulphur will dissolve copper, and with the latter it forrey compound, used by dyers

Copper readily unites with melted tin, at a temperature much lower than that which is necessary to melt the copper; by whichof tin A ravity of which is greater than that of thestatues, cannon, and bells; and in a certain proportion thistelescopes, receiving a fine polish, and not being apt to tarnish Copper and arsenic make a brittle compound called _tombach_; and with zinc it makes the useful compound commonly called _brass_, in which zinc is about one third of its weight

Copper is sometimes found native; but coreen, or blue colour

Copper being an earlier discovery than that of iron, was for of horses; and the ancients had ait a considerable degree of hardness, so that a sword e

LECTURE XXV

_Of Iron_

Iron is a reatest hardness, the most variable in its properties, and the most useful of all the metals; so that without it it is hardly possible for any people to reat advances in arts and civilization

This iston, so as to be very subject to calcine, or rust, by exposure to the air The same is evident by the colours which appear on its surface when exposed to heat, and also when it is struck with flint; the particles that fly fro iron partially calcined In consequence of its readily parting with its phlogiston, it is capable of burning, like wood or other fuel, in pure air

Iron and platina have the property of _welding_ when very hot, so that two pieces may be joined without any solder

When iron is heated in contact with steaiston, while the rest unites with it, and makes inflamht, and becomes what is called _finery cinder_ This substance, heated in inflammable air, iain If the iron be heated in pure air, it also imbibes the water, of which that air chiefly consists, and also a portion of the peculiar element of the pure air

The solution of iron in spirit of vitriol produces _green copperas_; which being calcined, becomes a red substance, called _colcothar_

The precipitate of iron, by an infusion of galls, is the colouring uisticated alkali, is _Prussian blue_

Water saturated with fixed air dissolves iron, and reen colour to glass

Iron readily combines with sulphur When they are found combined by nature, the substance is called _pyrites_

The union of phosphoric acid with iron makes it brittle when cold, commonly called _cold short_; and the union of arsenic makes it brittle when hot, thence called _red short_

Iron unites with gold, silver, and platina, and plunged in a white heat into mercury, it becomes coated with it; and if the process be frequently repeated, it will become brittle, which shews that there is some mutual action between the thin plates of iron intoof it, and make the _tinned plates_ in co furnace it is brittle; and when it is white within, it is extre iston, it is softer, and may be filed and bored

Cast iron beco exposed to a blast of air when nearly e of inflammable air, and the separation of a liquid substance, which, when concreted, is called _finery cinder_ The iron generally loses one fourth of its weight in the process Crude iron contains o_, and the access of pure air probably assists in discharging it, by converting it into air, chiefly inflammable