COP

COP

( 342 )

copper, and cryftallizing, but this will notreadily afford a fait of that fine colour for whichthe acetite made from verdigris and diftilledvinegar is fa much valued. According to Prouft39 parts of the black oxyd produce with dif-tilled vinegar ioo parts of the acetite; and onthe other hand ioo parts of the fait decompofedday boiling potafh, give 39 or 40 of the blackoxyd. Hence its compofition is thus deduced.

Oxygen } mak!ll S of bIack ox 7 d } 39Acetous acid . . . . 61

100.

The diftillation of the acetite of copper fur-nifhes that pungent concentrated acid called radi-cal Vinegar , the preparation of which is perfect-ly fimple, and is defcribed under the articleAcetous Acid . In this cafe as in the diftillationof common verdigris, the operation of the heatmodifies, and confiderably alters the arrange-ment of the component parts of this fait.Though by eftimation it is reckoned to containabout 60 per cent, of acetous acid, no morethan about 52 are obtainable by diftillation, theremainder being changed by the heat, and by theoxygen of the copper (7.8 per cent.) and newproducts being formed probably by very com-plicated affinities. Thefe products are partlycarbonic acid and carburetted hydrogen, andpartly, as it appears, a portion of empyreumaticoil, which, towards the end of the procefs, givesa peculiar fimell and colour to the acid. A fmallquantity of the acetite fublimes as a white faitin the neck of the retort, or covering the upperpart of the heated mafs, which appears to be theacetite, little, if at all altered, except by lofingfome of its water of cryftallization.*

After the diftillation, a brown powder re-mains in the retort, which laft is alfo fometimeslined with a thin film of metallic copper. Thisbrown powder is copper, almoll metallic, butftill containing fome oxygen, and alfo mixedwith charcoal, according to M. Adet, in thefollowing proportions in 90 parts, viz. Char-coal, 4.50 ; Copper , 78 .66 ; and Oxygen, 6.84.

The entire products of the diftillation of ace-tite of copper, as given by M. Adet, may herebe inferted as they appear confiderably accurate.The undecompofed portion of 288 parts of thefait was 25.5, deducing this, and reducing theremainder to the centefimal proportion it willbe as follows;

Acetous acid

53

Copper . . 30 . 1 , \

Charcoal & Oxygen 4.3 r‘ le re ^ ual f 34-3J brown powder J

Remains for gas given out . . 12.7

100.0

The 30 parts of metallic copper (which wereaffually obtained by fubfequent redu&ion,) areequivalent to 37.5 of black oxyd in the unde-compofed fait, a quantity not much differingfrom that given by Prouft.

On account of the very high price of the dif-tilled verdigris, many experiments have beenmade by chemifts to produce an equally fineacetite of copper by a fhorter method. Wherethe obje£t is merely that of yielding radicalvinegar by fubfequent diftillation, it is not diffi-cult to combine acetous acid with any of thecupreous oxyds, or carbonated oxyds, and toproduce a faturated acetite, with cv withoutregular cryftallization ; but to form the beauti-ful blue-green fait for the painter or dyer is notfo eafy. The double decompofition of acetitedlead and fulphat of copper, as mentioned underAcetous Acid, appears to fucceed the belt, thefulphat of lead being entirely feparable by merefubfidence, and the green fupernatant liquoraffording by evaporation a very fine cryftallizedacetite of copper.

The natural combinations of copper with Ar-fenic and Arfenic acid have already been fullymentioned, together with the general mode ofanalyfis. With regard to the artificial arfeniats,Scheelc y found that when arfenic acid wasdigefted with copper filings a green folutionwas formed, and a blue arfeniat alfo precipi-tated. The fulphat, nitrat, and muriat ofcopper undergo no apparent change by arfenicacid, but the acetite is decompofed, and arfeniatis precipitated. But. all the cupreous falts aredecompofed by double affinity, by arfeniatedalkali of any kind; and a blue arfeniat of copperfalls down. Mr. Chenevix alfo has the follow-ing experiments: Arfeniat of ammonia wasadded to nitrat of copper, which cauled a doubledecompofition, and arfeniat of copper fell downin blue cryftalline grains. On evaporating theclear liquor and adding alcohol, another copiousdepofition of cryftais took place after a while,which were of' a ftill deeper blue and rhom-boidal, and were alfo arfeniat of copper, and notnitrat of copper, this latter fait being foluble in

* Adet. An Clum. tom. 47. 7 Elf-7 e -