1072 VERDIGRIS 



plates, if new, are now prepared, by rubbing them over with a linen cloth, dipped in 

 a solution of verdigris ; and they are laid up alongside of one another to dry If the 

 plates are not subjected to this kind of preparation they will become black, instead of 

 green, by the first operation. When the plates are ready, and the materials in a 

 fermenting state, one of them is put into the earthen vessel for 24 hours, in order to 

 ascertain whether it be a proper period to proceed to the remaining part of the process. 

 If, at the end of this period, the plate be covered with an uniform green layer, con- 

 cealing the whole copper, everything is right ; but if, on the contrary, liquid drops 

 hang on the surface of the metal, the workmen say the plates are sweating, and con- 

 clude that the heat of the fermented mass has been inadequate ; on which account 

 another day is allowed to pass before making a similar trial. When the materials 

 are finally found to be ready, the strata are formed in the following manner : The 

 plates are laid on a horizontal wooden grating, fixed in the middle of a vat, on 

 whose bottom a pan full of burning charcoal is placed, which heats them to such 

 a degree that the women who manage this work are obliged to lay hold of them 

 frequently with a cloth when they lift them out. They are in this state put into 

 earthen vessels, in alternate strata with the fermented materials, the uppermost and 

 undermost layers being composed of the expressed grapes. The vessels are covered 

 with their straw mats, and left at rest. From 30 to 40 Ibs. of copper are put into 

 one vessel. 



At the end of 10, 12, 15, or 20 days the vessels are opened to ascertain, by the 

 materials having become white, if the operation be completed. 



Detached glossy crystals will be perceived on the surface of the plates ; in which 

 case the grapes are thrown away, and the plates are placed upright in a corner of the 

 verdigris cellar, one against the other, upon pieces of wood laid on the ground. At 

 the end of two or three days they are moistened by dipping in a vessel of water, after 

 which they are replaced in their former situation, where they remain seven or eight 

 days, and are then subjected to momentary immersion, as before. This alternate 

 moistening and exposure to air is performed six or eight times, at regular intervals 

 of about a week. As these plates are sometimes dipped into damaged wine, the work- 

 men term these immersions one wine, two wines, &c. 



By this treatment the plates swell, become green, and covered with a stratum of 

 verdigris, which is readily scraped off with a knife. At each operation every vessel 

 yields from 5 to 6 Ibs. of verdigris, in a fresh or humid state; which is sold to 

 wholesale dealers, who dry it for exportation. For this purpose they knead the 

 paste in wooden troughs, and then transfer it to leathern bags, a foot and a half long 

 and ten inches in diameter. These bags are exposed to the sun and air till the ver- 

 digris has attained a sufficient degree of hardness. It loses about half ifys weight in 

 this operation ; and it is said to be knife-proof when this instrument, plunged through 

 the leathern bag, cannot penetrate the loaf of verdigris. 



Verdigris is a mixture of the crystallised acetate of copper and the subacetate, in 

 varying proportions. According to Vauquelin's researches, there are three compounds 

 of oxide of copper and acetic acid: 1, a subacetate, insoluble in water, but decom- 

 posing in that fluid, at common temperatures changing into peroxide and acetate ; 

 2, a neutral acetate, the solution of which is not altered at common temperatures, but 

 is decomposed by ebullition, becoming peroxide and superacetate ; and 3, superacetate, 

 which in solution is not decomposed, either at common temperatures or at the boiling 

 point ; and which cannot be obtained in crystals, except by slow spontaneous evapora- 

 tion, in air or in vacua. The first salt, in the dry state, contains 66-51 of oxide ; the 

 second, 44-44 ; and the third, 33'34. 



Distilled Verdigris, as it was long erroneously called, is merely a binacetate or super- 

 acetate of copper, made by dissolving, in a copper kettle, one part of verdigris in two 

 of distilled vinegar ; aiding the mutual action by slight heat and agitation with a wooden 

 spatula. When the liquor has taken its utmost depth of colour, it is allowed to settle, 

 and the clear portion is decanted off into well-glazed earthen vessels. Fresh vinegar 

 is poured on the residuum, and if its colour does not become deep enough, more 

 verdigris is added. The clear and saturated solution is then slowly evaporated, in 

 a vessel kept uniformly filled, till it acquires the consistency of syrup, and shows a 

 pellicle on its surface ; when it is transferred into glazed earthen pans, called oulas in 

 the country. In each of these dishes two or three sticks are placed, about a foot long, 

 cleft till within two inches of their upper end, and having the base of the cleft kept 

 asunder by a bit of wood. This kind of pyramid is suspended by its summit in the 

 liquid. All these vessels are transported into crystallising rooms, moderately heated 

 with a stove, and left in the same state for 15 days, taking care to maintain an uniform 

 temperature. Thus are obtained very fine groups of crystals of acetate of copper, 

 clustered round the wooden rods ; on which they are dried, taken off, and sent into 

 the market. They are distinctly rhomboidal in form, and of a lively deep blue colour. 



