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tity of water remains in their compofitions, andis expelled, when by calcination the cupreousfait is converted to the black or brown oxyd aswas the cafe in this inftance. It is fortunatethat the experimenter himfelf enables us tocorrect the error, (which is merely that of com-putation) without obliging us to impeach theaccuracy of fo excellent a chemift. From thefacts given, therefore, we may fafely corredt therefults in the following manner.

The button of copper actually obtained fromthe refidue was in the proportion of 49 per cent,of the verditer, which (confidering the unavoid-able lofs by faline fluxes) may fairly be taken,with the author, at 50.

Fifty grains of copper require 12.5 of oxygento be reduced to the ftate of the black oxyd,which, as we have already feen, is the degree ofoxygenation in which the metal exifts in thenitrat. This again (according to Prouft) wouldrequire 20.8 of water to bring it to the ftate ofhydrat. But it is alfo clear that the weight ofcarbonic acid is much over-rated through fomeAngular overfight. The quantity actually ob-tained from 600 grains of verditer was about 2French pints, the weight of which, accordingto Lavoifier, would be only 66 French grains,and confequently 100 grains would yield onlyxi of this acid. The quantity of water wasobvioufly only eftimated at random. The cor-related refult therefore of Pelletier’s experimentswould be,

grains

Copper . 50.

Oxygen 12.5 V 83.3 Hydrat of CopperWater . 20.8 J

Lime . . 7.

Carbonic acid . 11.

iQi-3

which correfponds very clofely with the quan-tity analyzed. It may be added, however, thata very great difference in the proportion of in-gredients is found in the different forts ofverditer. The above analyfis is of the beft fort.

The fame chemift’s experiments on the com-pofition of this curious colouring matter areequally interefting. The precife difficulty appearsto be to preferve the blue colour, and prevent itfrom acquiring the fhade of green, which pro-perly belongs to the carbonats of copper. Ifnitrat of copper, or any other cupreous folutionis precipitated by a carbonated fixed alkali, thecolour is a deep apple-green. This, when

• Pelletier, tom. I. » Leonhard!.

rubbed with lime, aflumes a fine blue at firft,but by deficcation it again returns to nearly itsoriginal green. It appears neceftary, therefore,to ufe lime as the precipitant in the firft inftance,and not a carbonat, but here alfo M. Pelletierfound by varied trials that the precipitate was atonce blue when fomewhat more lime was addedthan was neceftary entirely to decompofe thenitrat, but when the ingredients approached tomutual faturation, or efpecially if the cupreousfolution was in excefs, the colour became green.This laft however became blue by a frefti addi-tion of lime, and in this method he propofes tomake the colour, as follows: add lime to adilute nitrat of copper, juft or hardly fufficientto decompofe the whole. This gives a greeniffiprecipitate, which iliould be well wafhed andnearly dried on a cloth ftrainer. Then rub itwith a frefti portion of lime, from 8 to 10 per-cent. of its weight, which will immediatelygive it a fine and permanent blue, and dry itflowly. The precife quantity of lime and pre-cipitate muft be determined by experience, andby the {hade of colour produced during themixture, obferving that lime will heighten theblue, and the green precipitate will foften it.

The Muriatic acid diffolves copper with diffi-culty, except when concentrated and boiling,when hydrogen gas is given out; but its oxydswith much more eafe, particularly the greenwatery oxyd. Thus if plates or ftireds ofcopper be only moiftened with muriatic acid,and expofed to the air, the furface very fpeedilybecomes covered with a green muriated oxyd,which a frefti quantity of the acid of very mo-derate ftrength will eafily diffolve; and by re-peating the procefs, a very ftrong folution may bemade. This folution, when hot, or very highlyconcentrated, is brown, but by dilution becomesgrafs-green. By careful evaporation and cool-ing the fait cryftallizes in rhomboidal prifmaticparallelipipeds, with fome varieties, 0 or whenmore haftily conduced, in feathery cryftals.Thefe are commonly deliquefeent, but whenboth the copper and the acid are free from ironthey are permanent .p This fait is very folublein water and alcohol. The latter takes up itsown weight when boiling, and part feparatesagain in very perfect cryftals. The compofitionof this cryftallized fait is thus given by Prouft 11 ,Black oxyd of copper 40Muriatic acid . 24

Water . . 3 6

loo,

’ An. dc Chioi. tom. 33.

2 U .

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