Gypsum is a compound of sulphuric acid with lime, and were it always pure, its effects upon wine would be imperceptible; but as the most kinds of common gypsum contain abundance of carbonate of lime, they effervesce with acids, are dissolved in part by them, and form that salt which I have before said I consider as harmless. By means of this carbonate gypsum improves sour wine, as well as common wine. I took half an ounce of that gypsum which at Osterode is pounded and used as mortar, and which is hard, white, and shining, and almost of the nature of alabaster. When I had pounded it, I put it into strong vinegar in a glass vessel, and suffered it to boil for a few minutes. I then strained it through filtering-paper; and what remained, after it was washed and dried, weighed 215 grains; so that the vinegar had dissolved 25 grains, which were precipitated afterwards by carbonated alkali. I pursued the like process with half an ounce of burnt gypsum, such as is used here for floors; and I found that two ounces of the same vinegar dissolved half a drachm of it, which was somewhat more in proportion than of the former. Every one whom I caused to taste of this vinegar remarked that both had lost a considerable share of their acidity; but that the vinegar which had been boiled with burnt gypsum had lost the most. Few kinds of native gypsum are perfectly pure; and at any rate we have no reason to suppose that the ancients sought pure gypsum for their wines. This method is not yet disused. We are told by Arvieux, that it is still employed in the island of Milo; and I shall here take occasion to observe that salt water also is added to wine there, even at present. Christopher Vega, whom I have before quoted, reproaches the Spaniards with the use of gypsum; and it has been condemned by the modern as well as the ancient physicians. An Englishman of the name of Hardy seems to suspect that gypsum contains lead and arsenical earth[730]; but it appears that this writer doubted whether our gypsum be the same as that of the ancients; and indeed it is necessary, before we use their information respecting natural objects, to examine carefully whether they understood by any name what we understand by it; and what they meant by gypsum has been determined neither by Stephanus, Ferber, nor Gesner. We however know this much, that the ancients burnt their gypsum, and that they formed and cast images of it[731]. In my opinion wine cannot be poisoned by gypsum; and wine-merchants who employ it and lime deserve no severer punishment than brewers, who, in the like manner, render sour beer fitter to be drunk and more saleable.