Zinc.
The ancients were acquainted with a mineral to which they gave the name of Cadmia,[[315]] from Cadmus, who first taught the Greeks to use it. They knew that when melted with copper it formed brass; and that when burnt, a white spongy kind of ashes was volatilized, which they used in medicine.[[316]] This mineral contained a good deal of zinc; and yet there is no proof remaining that the ancients were acquainted with that metal. It has a brilliant white colour, with a shade of blue, and is composed of a number of thin plates adhering together; its specific gravity is 7·1. When strongly heated in a crucible, it quickly goes into fusion, absorbs the oxygen of the atmosphere, and burns with a beautiful white flame, inclining to green, and extremely brilliant. The oxide of zinc thus formed, is diffused through the atmosphere, and is there condensed into extremely light flakes of a beautiful white appearance. This oxide was formerly known under the fanciful names of nihil album; lana philosophorum, &c.
In its metallic state it is quite inert; but late experiments by Vauquelin and Deyeux, have proved that it is very easily acted upon by water, the weakest vegetable acids, some saline substances, and butter; a fact which is hostile to the proposal of employing this metal for the manufacture of culinary utensils.
White Vitriol. Sulphate of Zinc.
This salt occurs in masses, consisting of crystals which are four-sided prisms, terminated by four-sided pyramids. Their taste is styptic, metallic, and slightly acidulous. They are soluble in 2·5 times their weight of water at 60°, and in less than their own weight of boiling water, but they are quite insoluble in alcohol. Thus dissolved they redden the tincture of tournesol.
Symptoms of Poisoning by Sulphate of Zinc.
This salt, like tartarized antimony, from the high degree of emetic virtue which it possesses, generally proves its own antidote; still, however, it must be considered as a poison; for several cases are on record, where the most alarming symptoms, and indeed death itself, have been the effect of its ingestion. Metzger[[317]] mentions the case of a woman, who accidentally ate a trifling quantity of a cake, into which White Vitriol had been introduced for the purpose of shortening the days of an old man. The woman died; but the intended victim escaped, after severe vomiting. M. Orfila has also related several cases of poisoning by this salt. The symptoms which presented themselves on these occasions were, an astringent metalline taste, a sense of constriction in the fauces, so distressing as even to excite in the patient a fear of suffocation; frequent vomitings; copious stools; pains in the epigastric region, extending afterwards over the whole abdomen; difficulty of breathing; frequency of pulse; paleness of the countenance, and coldness of the extremities.
We have lately heard of a case in which a noble lord swallowed a solution of white vitriol, which had been sent to him by mistake, for Epsom salts, to which it bears some analogy. Fortunately, however, the violent emetic effect which followed removed the poison from the stomach, and obviated any farther injury.
Organic lesions discovered on Dissection.
We have no well authenticated dissection of a human being who had died from the ingestion of this poison. The examination of animals[[318]] who have been so killed has shewn nothing more than an inflammation, not very severe, of the membrane with which it had come in contact; sometimes dark blood is observed to be extravasated upon the muscular coat of the stomach and intestines.