COP
COP
( 341 )
parat'on, a certain difference is found in theappearance of the two kinds, that of Mont-pellier having a foft greafy feel v , and (hewingin its frafture a number of filky filaments likefome kinds of malachite, and alio being almoftinfoluble in water. The other kind is dryerand harfher to the touch, of a deeper colour,breaking more like the cryftallized fait, andmore foluble in water. The former is fome-what cheaper and is preferred in painting, thelatter is more ufed in dyeing. The analyfis ofeach bv diftillation per fe with a graduated fire,(lowly increafed till every thing volatile was ex-pelled, gave as follows.
Carbonic acid -
9.10
Water weakly acidulous
! 3 -Q 5
Strong, coloured acetous acid
53-95
Copper 7 left i n the
20.90
Charcoal S retort
3.00
100.00
A hundred parts of the verdigris from Mont-pellier gave
Carbonic acid - 8.00
Acetous acid very weak and very 1 ^
empyreumatic - J ^
Copper - 22.50
Charcoal - - - - 4.35
100.00
In comparing thefe products it will be foundthat the difference may principally be explainedfrom the different mode of manufacture. Itmay be premifed that the products thus ob-tained by fire are by no means in the fame (lateof combination in which they exift in the fait:the heat decompofing much of the acetous acid,(befides what is Amply expeiied) and thenceproducing carbonic acid in abundance, and pro-bably oxyd of carbon not noticed in this ana-lyfis, whilft the oxyd of copper is alfo decom-pofed, the oxygen uniting with the new com-pounds, and the copper being left very nearlyin the metallic (late, and mixed with a littlecharcoal from the vegetable matter. From themuch lefs quantity of acetous acid, and thegreater degree of empyreuma in the product ofthe Montpellier verdigris than in the other, itis reasonably inferred to contain more extractivematter, and lei's acid in its natural (late, asmight be expedted, where an imperfectly fer-mented refuic matter is ufed indead of pure
* Jcur. des M
acetous acid in the manufacture. The Mont-pellier kind therefore is a fub-acetated oxyd ofcopper mixed with vegetable extractive matter:the Grenoble kind is almoft pure fub-acetite,and the part foluble in water is doubtlefs theperfeCt acetite.
The analyfes both of verdigris and of theacetite of copper as given by Proult, (hew avery different proportion of ingredients in thefub-acetite from that juft mentioned. As theoxyd of copper is the only fubftance aCtually ob-tained in Proud’s analyfis, the difference maybe explained, partly by the different date ofdrynefs of the fubltance on which thefe twochemifts operated, and partly by fuppofing thatthe one took the entire verdigris, and the otherthe pure fub-acetite feparated from commonverdigris by diffufion in water. Proud ob-ferves, that when verdigris is put into coldwater it gradually falls to pieces, near one-halfis diffolved (and hence the kind here examinedmore approaches that of Grenoble ) and the re-mainder is a very fine green powder whichdiffufes itfelf through the water, and fub-fides extremely (lowly, together with the acci-dental impurities of the copper. This greenpowder appears to be the pureft fub-acetite ofcopper, and when wafhcd and dried weighsabout 42 per cent, of the original verdigris.When fulphuric acid is poured on it pungentvapours of vinegar are given out. Boiled withpotalli, a black perfeCt oxyd of copper is ob-tained, in the proportion of 63 from 100 of thefub-acetite. Diddled per fe the produds arethe fame in kind with thofe of the acetite ofcopper (which will be prefently mentioned).andthe refidue is 52 per cent of copper almoft. inthe metallic ftate, but not entirely, fince colddiluted fulphuric acid is coloured blue by re-maining in it, diffolving the fmall portion ofoxyd of copper, and leaving the metallic partuntouched. According to this analyfis there-fore, ioo parts of the fine green fub-acetite ex-trafted from verdigris by diffufion in waterand dried, are compofed of
Oxygen forming the black oxyd 63
Remains for acid and water - 37
100.
Acetite of copper (meaning the cryftallizedand perfectly faturated fait, or the dijiilled ver-digris ) may be produced, for experiment, limplyby faturating diftilled vinegar with oxyd ofnee* No. 75.