The alchymists believed, they could obtain, from nitre, a liquor, which would constitute, with other substances, the _philosopher's stone_. The _clyssus_ of nitre, they imagined, possessed wonderful properties. The decomposition of nitre by charcoal, they effected in two ways, _viz._ by submitting the mixture to the action of heat in a crucible, or, otherwise in an earthen or iron retort. In the latter case, they collected a fluid, principally water, containing some carbonic acid, and the aeriform product they suffered to escape. The residue they named _nitre fixed by charcoal_, or, _the extemporaneous alkali of nitre_. When, in the place of charcoal, a mixture of sulphur and nitre was projected into a red-hot crucible, they obtained a saline substance, to which they gave the name of _sal polychrest_. This is the same as vitriolated tartar, or sulphate of potassa, and is that salt which is formed in the distillation of nitric acid from nitre, and sulphuric acid. The _crystal mineral_, of some of the old pharmacopœias, was nothing more than nitrate of potassa fused with a portion of sulphur, and, therefore, a mixed salt, consisting of nitrate and sulphate of potassa. Nitrate of potassa, distilled with half its weight of sulphuric acid, furnishes nitric acid, or concentrated spirit of nitre. This, diluted with about an equal weight of water, forms the _aqua fortis_ of the shops. A mixture of nitre and phosphorus, if struck with a hammer, produces a violent detonation. Nitre oxidizes all the metals at a red heat, even gold and platinum. Nitre and sulphur, thrown into a red-hot crucible, produces an instantaneous combustion, accompanied with a great disengagement of light and heat. Sulphurous acid gas, with sulphuric acid, is produced. Equal parts of cream of tartar, (supertartrate of potassa,) and nitre, deflagrated in a crucible, form _white flux_. Two parts of tartar, and one of nitre, treated in the same manner, produce _black flux_. Three parts of nitre, one part of sulphur, and one part of sawdust, mixed together, form the _powder of fusion_.