The best verdigrease is mostly manufactured at Montpelier, in France, by forming alternate strata of copper-plates, and the husks of grapes, during their vinous fermentation ; tation ; when they speedily become acid, and corrode the copper: alter the plates have stood in such situation for a sufficient time, they are moistened with water, and exposed to the air; the verdigrease being successively scraped off, as it collects on the surface. In this state, the acetite is called fresh or moist verdigrease, having the form of paste; which, after triturating it in proper troughs, is put in bags, and dried in the sun. - It pays, on importation, a duty of 3 1/2d. per lb.
Crystals of Verdigrease are prepared by saturating vinegar with the common acetite of copper, and leaving the solution to clarify; after which it is poured into a kettle, where it is evaporated till a pellicle appear on the surface: when cool, the vessel is furnished with small sticks, on which the crystals gradually settle : - they are subject in the Custom-house to the charge of 1s. l 11/2d. per lb.
Verdigrease is chiefly consumed for striking a black colour, when combined with a decoction of logwood ; but, as it is apt to corrode the texture of the cloth, the Society for the Encouragement of Arts, etc. in 1782, conferred their silver medal and ten guineas on Mr. Clegg, for his discovery of a substitute for verdigrease, in dyeing black. He directs equal parts, by weight, of vitriol of copper and of pot-ash, or other strong alkaline salt, to be separately dissolved : the solutions are then, to be gradually mixed ; and, if the vitriol be saturated, the water on the surface will become transparent, on adding a drops of the alkaline solution : in the contrary case, a blue colour will be produced ; so that more ashes should be added, till a com-saturation be effected. Mr.
C. observes, that these proportions of vitriol and alkaline salt, will be equivalent to a similar quantity of verdigrease; and, on being combined with decoctions of logwood, they impart a fine black dye, which is not injurious to the texture of cloth, hats, or any other article that may be tinged of such colour. Verdigrease is, in surgical cases, sometimes applied externally; it operates as a mild detergent in cleansing foul ulcers, or other open wounds. - On account of its virulent properties, however, it ought not to be used as a medicine, without professional advice; and, in case any portion of this poisonous substance be accidentally swallowed, we refer to the remedies already pointed out, vol. i. pp. 74-75.