It merits notice, however, that in certain cases of poisoning by copper, no vestiges of the substance can be found in the matters voided from the stomach. In that case, _Orfila_ directs that the mucous membrane of the stomach, and of the intestines, should be scraped off, dried, and submitted to the action of a strong heat in a crucible. “I have,” says this distinguished experimentalist, “twice obtained metallic copper, by calcining in this manner a portion of the membranes of the stomach of two dogs that I had poisoned with verdegris. This effect particularly takes place when the mucous membrane is of a bluish colour, hard, and strongly adhering to the substance of the stomach.” TIN and its MURIATE. It is clearly established by the experiments of _Bayen_ and _Charlard_,[313] as well as by those of _Proust_,[314] that this metal possesses no poisonous properties. Its muriate, however, has been shewn by _Orfila_ to possess highly corrosive properties. It excites violent vomiting, great depression, and death, without convulsions. Its antidote is milk, which it speedily coagulates; and by chemical combination with it, the poison is rendered inert. On dissection, the stomach is said to have been found corrugated and indurated, and has been compared to tanned skin, but its colour is not altered. As this substance is never likely to become an object of forensic interest, in this kingdom, we shall pass it over without farther notice. 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._