COP

COP

( 340 )

too clofely prefled, or, if poor, it fhcukl bemoiftened with a little ordinary wine. To de-termine when the marc is fufficiently fermented,a fmall copper plate is buried in it for twenty-four hours, and if fit, the plate will come outcovered uniformly with a green cruft. Theplates are then all heated fcorching hot over apan of charcoal, and laid regularly in earthenpots with a layer of the fermented marc at bot-tom and at top, and interpofed between eachplate. The pot is then loofely {topped with ftraw,and the whole left at reft from ten to twentydays. Thefe earthen pots (the fame in whichthe marc is fermented) are about 16 incheshigh, and 14 in diameter, and the mouth 12inches. Each holds about 30 or 40 pounds ofcopper plate, with the requilite quantity ofmarc. When the plates are ufed for the firfttime they are previoufly prepared by being rub-bed with a rag dipped in a folution of verdigrisin water, and fuffered to dry. Without this thefirft produce of verdigris is apt to be black.This is not required a fecond time.

The earthen pots are emptied when the marcbegins to whiten, and if the procefs has goneon well, the copper plates are found coveredwith a green cruft interfperfed with diftindtfdky green cryftals. They are then taken out (themarc being thrown away) and fet on end faceto face on wooden racks in a cellar; and whendry they are dipped in water (formerly in wine)and again fet to dry, and this is repeated oncea week for fix or eight times which makesthem l'well, and in every way improves andencreafes the crop of verdigris, which is finallyfcraped off with a knife without difficulty.Every pot yields about five or fix pounds ofrough verdigris, and the plates, after this is fe-parated, will ferve again repeatedly till they arecorroded quite through.

The verdigris is fold by the maker in therough ftate, and is further prepared by being wellground in wooden mortars and expofed to theair on Ikins till fufficiently dry, in which pro-cefs it lofes nearly half its weight. The wholeof the manufacture of the rough verdigris is apart of houfehold bufinefs in the wine-farmsabout Montpellier , and is generally done by thewomen. It requires little attendance, and noother capital than the expence of the copperplates and earthen jars.

Verdigris thus prepared may be confideredas copper oxydated by the aftion of the acetousacid of the fermented materials, united withwater, and a fmall portion of undecompofed

acetous acid, together with part of the ex-tractive or mucilaginous matter of the marc.Its exadt compofition will be prefently men-tioned. I11 this ftate it is infoluble, or nearlyfo, in water. The colour is a fine green, and itis ufed more largely as a pigment than anyother cupreous preparation.

Verdigris is however completely foluble in anadditional portion of vinegar, and the refult isthe perfect acetite of copper, a beautiful cryftal-lizable fait, fold at a very high price in the {hopsunder the name of diftilled verdigris. It is pre-pared from common verdigris in Holland andFrance, and Montpellier ; the procefs which isfollowed at the latter place is very fimple,and is thus deferibed by the fame accurateobferver. Common vinegar is firft diftilled in acopper alembic, which feems to be a procefsconftantly going on in the fmall way in moft ofthe vintage farms in the neighbourhood. Thisis put with common verdigris into a copperboiler, and when a hot faturated folution ismade, it is {trained and let off to another copperevaporating veffel, where it is boiled down tilla cruft of the fait appears on the furface. Alight frame of flicks in crofs-bars is then funkin the liquor and the fire put out. On cooling,the acetite of copper crufts around the flicksin moft beautiful clutters of rhomboidal cryftalsof a fine deep blue-green colour. When thefeare dried and finely powdered they form a greenpigment of great beauty and value. It requiresabout three pounds of verdigris to make onepound of the cryftallized acetite. The partwhich remains undiffolved in the vinegar con-fifts of an imperfect oxyd or acetite which ufedto be thrown away, but, as Chaptal has ob-ferved, when moiftened occafionally with vine-gar, and expofed to the air, it yields a frefhquantity of verdigris, and is then readily folublein vinegar.

From the analyfis of feveral chemifts thereappears to be very little uniformity in the pro-portion of the ingredients of the common ver-digris, but according to Chaptal two kinds areparticularly diftinguifhed in France , that ofMontpellier, and that of Grenoble . The latteris prepared in a different manner from that al-ready deferibed, no fermented refufe of the vin-tage being here ufed, but the procefs is chieflyto difpofe plates of copper in a proper room,and to moiften them repeatedly with diftilledvinegar till the furface is fufficiently oxydatedand converted into verdigris.

In confequence of this difference in the pre-