_Sulphur_ has been mentioned before; it is well known to be a very combustible substance; it is found in great quantities throughout nature; the sulphur of commerce comes either from Italy or Sicily; or from the isle of Anglesea, where it is obtained from the smelting of sulphuret of copper; the best, however, comes from Sicily. It is, sometimes, found pure; but often combined with some of the metals, forming _sulphurets_. It is also frequently obtained by the decomposition of animal and vegetable substances; it is sometimes found combined with hydrogen (hence called sulphuretted hydrogen), in the human stomach, more frequently in the intestines. Sulphur combined with a small dose of oxygen, forms a volatile suffocating acid, called the _sulphureous acid_; with a large dose it forms _sulphuric acid_, or oil of vitriol. For the _nitric_ and _muriatic acids_, see a preceding section. We may, however, mention here, that nitric acid has the peculiar property of staining the _scarf skin_ of the human body a dull yellow, of such permanence, that it can scarcely, by any means, be destroyed, it usually remaining till the skin wears or peels off. The principal vegetable acids are the _tartaric_ and the _acetic_. The tartaric acid exists in superabundance in tartar, and particularly in cream of tartar, which is nothing more than a purified tartar. See _argol_ in a preceding section. The _acetic acid_ constitutes the vinegar both common and distilled; it is found in a very concentrated state in the shops, under the name of _aromatic vinegar_. It is also now obtained in large quantities, and of great strength from _wood_ by distillation, or burning, in vessels, adapted for the purpose, hence called the _pyrolignous_ acid, but essentially the acetic acid. This last is now used by Calico-Printers to make acetate of iron. See a preceding section. _Alumina_, or earth of alumina, sometimes called _argil_, is soft to the touch, adheres to the tongue, and hardens in the fire, contracting its dimensions: it constitutes the greatest part of clays. With sulphuric acid and pot-ash, it forms the common alum of the shops. Alum dissolves in about sixteen times its weight of cold water. For _acetate of alum_ see _alum_ in a preceding section.