Vitriolic acid, even concentrated and boiling, has but little effect upon bismuth; but the nitrous acid acts upon it with the greatest rapidity and violence, producing much nitrous air, mixed with phlogisticated nitrous vapour. From the solution of bismuth in this acid, a white substance, called _magistery of bismuth_, is precipitated by the affusion of water. This has been used as a paint for the skin but has been thought to injure it. The marine acid does not readily act upon bismuth; but when concentrated, it forms with it a saline combination, which does not easily crystallize, but may be sublimed in the form of a soft fusible salt, called _butter of bismuth_. Bismuth unites with most metallic substances, and in general renders them more fusible. When calcined with the imperfect metals, it unites with them, and has the same effect as lead in cupellation. Bismuth is used in the composition of pewter, in printers' types, and other metallic mixtures. This metal is sometimes found native, but more commonly mineralized with sulphur. LECTURE XXVII. _Of Nickel._ Nickel is a semi-metal of a reddish cast, of great hardness, and always magnetical; on which account it is supposed to contain iron, though chemists have not yet been able to separate them. The purest nickel was so infusible as not to run into a mass in the strongest heat of a smith's forge; but then it was in some degree malleable. Concentrated acid of vitriol only corrodes nickel. Alkalies precipitate it from its solution in the nitrous acid, and dissolve the precipitate. It readily unites with sulphur. Nickel is found either native or mineralized with several other metals, especially with copper, when it is called _kupfer nickel_, or _false copper_, being of a reddish or copper colour. This semi-metal has not yet been applied to any use. _Of Arsenic._ What is commonly called _arsenic_ is the calx of a semi-metal called the _regulus of arsenic_. It is a white and brittle substance, expelled from the ores of several metals by heat. It is then refined by a second sublimation, and melted into the masses in which it is commonly sold. This calx is soluble in about eighty times its weight of cold water, or in fifteen times its weight of boiling water. It acts in many respects like an acid, as it decomposes nitre by distillation, when the nitrous acid flies off, and the _arsenical salt of Macquer_ remains behind. When the calx of arsenic is distilled with sulphur, the vitriolic acid flies off, and a substance of a yellow colour, called _orpiment_, is produced. This appears to consist of sulphur and the regulus of arsenic; part of the sulphur receiving pure air from the calx, to which it communicates phlogiston; and thus the sulphur becomes converted into vitriolic acid, while the arsenical calx is reduced, and combines with the rest of the sulphur.