This substance forms spontaneously on surfaces of copper and brass; it differs from the oxide in its green colour, and in effervescing with dilute sulphuric acid; with ammonia, however, it demeans itself in the same manner, and is likewise insoluble in water. It is poisonous.
From the above history of these substances the medical practitioner will easily perceive under what circumstances, and by what bodies, metallic vessels of copper may be rendered dangerous. The oxide and carbonate, formed in them, will easily dissolve in acidulous and oily aliments, whence it follows that all preparations of such food, if conducted in vessels whose surfaces have contracted this change will be liable to prove deleterious.[[309]] If the vessels be perfectly clean, acid preparations may be safely boiled in them, but they must be poured out immediately, and not suffered to remain sufficiently long to allow the copper to become oxidized. To the formation of the oxide of copper, and to the acetic acid contained in the wine, vinegar, beer, and cider, M. Orfila attributes the production of the acetate which forms about the corners of the cocks in vessels containing these liquors. Upon the same principle the soda water sold in this town, in a draught, from the pump, is liable to metallic impregnation, as we have fully satisfied ourselves.
Equally important is it for the forensic physician to be acquainted with the various other sources from which copper poison may be derived. In consequence of the fact of the oxide of copper forming, with the acids, compounds of a beautiful green colour, the metal is often employed in cookery to impart a vivid hue to various articles; the sale of pickles, for instance, frequently depends upon the liveliness of their green colour; whence we find, in works[[310]] on cookery, directions for ensuring such an effect, by boiling the pickles with copper coin, or by suffering them to stand for some time in vessels of that metal. In the third volume of the Medical Transactions of the College of Physicians we shall find an interesting history, related by Dr. Percival of Manchester, of a young lady who amused herself, whilst under the hands of the hair-dresser, with eating pickled samphire, of which she consumed two breakfast plates full; she shortly afterwards complained of great thirst, pain in the stomach, and a rash appeared upon her hands and breast. After an illness of nine days, during which she suffered severe vomitings, and tormina of the bowels, she expired. Upon examining the samphire, Dr. Percival found that it was very strongly impregnated with copper. In the preparation of confectionary, especially sugar-plums, and sweatmeats of a green colour, copper is very generally introduced, and many instances are recorded of their having proved highly deleterious. Catsup is also said to be occasionally impregnated with verdegris; and vestiges of this metal have been detected in the well known cordial, called Shrub.
In order to prevent the contingent dangers attendant upon copper vessels, they ought always to be tinned;[[311]] and it is a very curious and interesting fact, that this latter metal, although it may cover the copper surface only imperfectly, will nevertheless protect us from its effects; for M. Proust has shewn that the superior readiness with which tin is oxidized and acted upon by acids, when compared with copper, will not allow this latter metal to appropriate to itself a single atom of oxygen.
But copper vessels, notwithstanding this fact, unless well tinned, should be dismissed from the service of the kitchen. The Senate of Sweden, in the year 1753, prohibited them entirely, and ordered that none but such as were made of iron should be used in their fleets and army.
Verdegris. Ærugo.
The verdegris of commerce is a compound mass, consisting of the acetate, and sub-acetate of copper, carbonate of copper, and copper partly metallic, and partly oxidized; it, moreover, contains the stalks of grapes and other extraneous matter. Boiling water dissolves it in part, and, at the same time, occasions in it a chemical change, by transforming one portion of the sub-acetate into the soluble acetate, and another, into an oxide of copper, which is precipitated. With cold water, verdegris demeans itself very differently; the acetate is dissolved by it, whilst that portion which is in the state of sub-salt remains suspended in the form of a fine green powder. Vinegar converts all the ærugo into a soluble acetate. Sulphuric acid poured on its powder decomposes it with effervescence, and vapours of acetic acid are disengaged; a character by which this substance may be easily identified.
Blue Vitriol. Sulphate of Copper.
Blue Copperas—Roman Vitriol.
This salt occurs in crystals of a deep rich blue colour, and whose form is that of a rhomboidal prism; their taste is harsh, acrid, and styptic; on exposure to air they slightly effloresce, and assume a greenish hue. When treated with sulphuric acid, no effervescence occurs, a circumstance which at once distinguishes this salt from ærugo.