COP

COP

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alcohol, and therefore not precipitnble by it.Each of thefe arfeniats was examined feparately,firft by calcination in a low red heat to expelthe water, then by potafh to obtain the blackoxyd of copper, and laftly by nitrat of lead toeftimate the arfenic acid. By this method thefir It arfeniat was found to confift ofOxyd of copper 50Arfenic acid 27

Water . 22

99

The fecond deeper-coloured arfeniat confidedof Oxyd of copper 35.

Arfenic acid 39*5

Water , 24.

9 8 -5

Arfenic, in the date of white oxyd whencombined with oxyd of copper, forms a grafs-green powder, firft noticed by Scheele , andcommonly called in chemiftry Scheele’s Green.It is formed by decompofing arfeniated potafhby fulphat of copper, by double affinity. Thenitrat or any other fait will anfwer the famepurpofe. The inventor’s procefs for making itin quantity is the following : Diffolve 24 ouncesof fulphat of copper in water in a copper veffelover the fire -, and, feparately, in another copperveffel, 24 ounces of fine pearlafh, and 11 oz. ofwhite arfenic in water, alfo with heat, andftrain each folution feparately through linen.-,then add the arfeniated potafh, little by little,to the fulphat of copper, with conftant Itirring,which will immediately effervefce, and thenwill let fall a green powder. When the wholeis mixed, let it Hand fome hours, edulcoratewell with clear hot water and dry very gentlyin a warm room. From the above quantities184- ounces of the green powder are obtainable,which may be ufed as a pigment.

Phofphat of copper may be made artificiallyby adding phofphat of foda to nitrat of copper,or any other cupreous fait. A blueiffi-greenfediment fettles, which dries to a powderymafs mixed with cryllals. A low red heatturns it brown and drives off all the water. Itlofes by this 15.5 of pure water. The refidueis a phofphat of copper, confuting of 35 ofphofphoric acid and 49.5 of oxyd of copper. 2

A ftriking decompofition of nitrat of copperalfo takes place when a flick of frefh-meltcdphofphorus is immerfed in this cupreous folu-

tion and expofed to light. By degrees thpcopper is precipitated in the metallic ftatg o»the phofphorus in cryftalline grains.

The Pruffic acid forms a red-brown fait withoxyd of copper. All the cupreous falts aredecompofed by pruffiat of potafh or of lime,and the colour of the precipitate (which nearlyrefembles that of metallic copper without theluftre) is different from that of any other pruffiat,and hence this may occafionally be ufed as aferviceable tell. By drying, the colour changesto a dark chocolate hue.

Tincture of galls added to the cupreous folu-tions gives a dirty yellow precipitate.

All the other acids diffolve the oxyds of cop-per, forming falts little known and of fmallimportance. In all of them, green in its variousfhades is the predominating colour.

Of the Alkalies, neither potafh nor foda haveany a£tion on copper or its oxyds, except that(fo often mentioned) of depriving the wet pre-cipitated oxyds of their water of combination,by the help of a boiling heat, and bringing themto the ftate of the black oxyd, compofed limplyof about 80 per cent, of copper and 20 of oxy-gen.

The carbonated fixed alkalies however diffolveoxyd of copper by help of the carbonic acid,and by evaporation a triple fait of carbonic acid,alkali, and oxyd of copper may be obtained, ashas been already mentioned.

Ammonia has no action on metallic copper,but diffolves its oxyds with eafe. The ufualcolour of this folution is a molt beautiful deepblue, and it is made in a variety of ways. Themolt dire£t way is to put together any oxyd orcarbonated oxyd of copper and liquid ammoniain a phial, and digeft them. The liquor becomesblue almoft immediately, which colour deepenstill the alkali is faturated. By flow evaporationcarefully managed, the ammoniated copper maybe got in fine blue filky cryllals. Alcohol addedwhen the folution is quite concentrated, muchaffills the cryftallization. This fait lofes itsalkali by expofure to air, and at the fame timeabforbs carbonic acid, fo that at laft a greencarbonat is left. Another method of makingthe ammoniated copper is to digeft in a glafs• veflel lime, muriated ammonia, verdigris, andwater. The lime firft decompofes the muriatedammonia and difengages the alkali, which thendiflolves the oxyd of copper, and very foonproduces a fine blue liquor, confilling thereforeof ammoniated copper and muriated lime. Limewater will anfwer as well, where only a. .weak.

* Clicr.cvix.