The plates are then moistened with water, and set up in racks, face to face, in a cellar: this is repeated once in seven days for six or eight times, until a thick coat of ver-digrise is formed, which is scraped off; and the copper plates again subjected to the same process, until they are completely corroded. When the plates are first used, the verdigrise is apt to be black, unless their surfaces be previously rubbed with a solution of verdigrise, which is suffered to dry before they are used.

1 Vide Chaptal's Account of the Manufacture, Phil. Mag. vol. iv. p. 71.

Verdigrise in this rough state is sold by the makers, who are generally women belonging to the wine farms about Mont-pellier, to commissioners, by whom it is further prepared. After being well beaten in wooden mortars, it is pressed down in bags of white leather, a foot in depth and ten inches wide, in which it is dried in the sun; and thus a loaf of verdigrise is formed, which cannot be pierced with a knife.

In this process the copper is oxidized, and the oxide combined with acetic acid, forming a diacetate, which is mixed with vegetable extractive matter and the stalks and husks of grapes. The Grenoble verdigrise is purer than the Mont-pellier, being prepared by simply disposing plates of copper in a proper situation, and repeatedly moistening them with distilled vinegar until the surface be oxidized, and changed into verdigrise.

The diacetate of copper is imported into this country in the leathern sacks, or bags, in which it is dried, each containing from fourteen to thirty pounds' weight. But it is also now prepared in Great Britain.

Qualities.-Good diacetate of copper is inodorous. It seems at first nearly insipid, although exceedingly styptic; but leaves a strong metallic taste in the mouth. The mass is dry, not deliquescent, of a hard, pulverulent, foliaceous texture, and a beautiful bluish green colour. Distilled water at 60° dissolves 0.56 parts, while 0.44 remain in the state of a fine green powder, long suspended in the solution : that part which is dissolved is an acetate of copper, consisting of 1 proportion of oxide of copper = 39.6 + 1 of acetic acid = 58.48, and 1 of water = 9, making the equivalent = 103.08, the filtered solution reddening litmus paper; whilst the insoluble powder is a diacetate, composed of 2 proportions of oxide = 79.2 + 1 of acid = 54.48 + 6 of water= 54, mixed with the impurities. When boiling water is used, the insoluble part is of a brown colour. Sulphureted hydrogen gas decomposes the solution, precipitating a black sulphuret of copper. A small cylinder of phosphorus put into the solution is rapidly covered with a coat of metallic copper.

1 40 lbs. of copper yield about five or six pounds of rough verdigrise.

Besides the stalks and husks of grapes, verdigrise is often adulterated with sand, and other earths. These are discovered by dissolving it in diluted sulphuric acid, which takes up the whole of the salt, and leaves the impurities; or by boiling it in twelve or thirteen times its weight of distilled vinegar, allowing the undissolved part to settle, and ascertaining its amount. The addition of muriate of baryta will detect any admixture of the sulphate or the tartrate of copper.

Medical properties and uses.-Verdigrise is tonic and emetic. It has been used in epilepsy; and extolled as an emetic in cases which require that the stomach should be quickly evacuated, without weakening it, as in incipient phthisis; but its internal exhibition is always dangerous, and to be avoided. It is, however, a useful detergent and escharotic application to foul ulcers, and the callous edges of sores; and to consume fungus; but it is seldom used, although it is milder than the sulphate. It is also employed as a collyrium in chronic ophthalmia.1

The dose of verdigrise to produce its tonic effect is under gr. ss.; that which is necessary to operate as an emetic, from gr. j. to grs. ij. In overdoses it quickly proves fatal, acting both locally and on the nervous system; the symptoms are colic pains, profuse vomiting and purging; sometimes salivation; convulsions, palsy, and fatal coma. On dissection, the coats of the stomach appear much thickened from inflammation; there is ulceration of the mucous membrane of the intestines, sometimes gangrene, and the whole is of a green colour. We formerly suggested the idea that fine filings of iron might precipitate the copper in its metallic state, and operate as an antidote, and that the experiments of Duval and others had proved that sugar is the antidote of cuprous poisons1; but our own experience since does not authorise an acquiescence in this account : and sugar reduces the salts of copper only by long ebullition. The best antidotes yet suggested are albumen and the ferrocyanate of potassa.

1 Dr. Paris (Pharmacologia) says, that it is the active ingredient in Smellome's Eye Salve, a nostrum in much repute.

Officinal preparations.- Cupri Subacetas prceparata, D. Uh-guentum Subacetatis Cupri, E. Oxymel Cupri Subacetatis, D.

2. Acetate of Copper.

Officinal. Cupri Acetatis Crystalli, Dub. Crystals of Acetate of Copper. Syn. Verdet crystallise, Cristaux de Venus (F.), Destillirten Grunspan (G.).

This salt is manufactured both in France and Holland. It is easily obtained by dissolving 100 parts of verdigrise in 200 parts of distilled vinegar heated to boiling. When the solution is completed, it is poured off clear from any undissolved matter, and evaporated until ready for crystallization. The crystals are generally formed upon sticks, in conical masses. About three pounds of verdigrise are required to make one pound of crystals.

Qualities.-Crystallized acetate of copper has a deep green colour: the crystals are semi-translucent octahedrons, with a rhomboidal base. The taste is acrid. Exposed to the air, acetate of copper effloresces; and when heated is decomposed, giving off gaseous or anhydrous acetic acid, the metal reduced mixed with charcoal being left in the retort. It is soluble in 20 parts of cold water; in 5 of boiling water, and crystallizes on cooling; and in 14 of alcohol. Acetate of copper consists of 1 eq. of protoxide = 39.6 + 1 of acid=51.48 + 9 of water = 81, making the equivalent =181.08, acid and water 61 + oxide of copper 39, in 100 parts.

Medical properties and uses.-This salt possesses the same properties, and is used for the same purposes, as rough verdigrise.