urine, that had been putrid for a considerable time. 9. To these may also be referred, a mass composed of equal parts of sulphur and iron-filings; which, when thoroughly moistened with water, after some time, grows hot, swells, and at last breaks out into vapour, smoke, and flame. (See _Artificial Volcano_.) Cadet's fuming liquor, prepared by distilling equal parts of acetate of potassa, and arsenious acid, emits a very dense, heavy, fetid, noxious vapour, which inflames spontaneously in the open air. Black wadd, an ore of manganese, when dried by the fire, and mixed with linseed oil, gradually becomes hot, swells, and then bursts into flame. M. Chenevix (_Annales de Chimie_, tom. LXIX,) remarks that almost all the metallic residuums, which are formed by the distillation of acetates _per se_, are pyrophoric, after cooling; which Mr. C. attributes to the presence of finely divided charcoal, mixed with the metallic part. He experimented on several acetates, with the view of ascertaining the quantity of pyroacetic spirit they would yield, and found, in every instance, that charcoal existed in the residue, sometimes with reduced metal, and at other times with metallic oxide. A table of these experiments may be seen in Ure's _Chemical Dictionary_. The residuum of acetate of copper has long been known to possess pyrophoric properties. _Sect. XXXIII. Of Sal Ammoniac._ This salt enters into the composition of fire-works, to give, more particularly, a peculiar colour to flame, which is that of green, or yellowish-green. Sal ammoniac is a salt, composed of muriatic acid and ammonia, and, when pure, is white, and capable of being sublimed without decomposition. Its purity may be known by its complete volatilization. It is readily pulverized. The experiment, showing the formation of sal ammoniac by a direct union of its component parts, may be made by bringing in contact, in a glass receiver, muriatic acid gas and ammoniacal gas. White clouds will form, a condensation take place, and muriate of ammonia be deposited on the sides of the vessel. Sal ammoniac was altogether made, at one period, from the soot of camels' dung, or of other animals, which feed on saline plants. The excrement was burnt, the soot collected, and sublimed. This was the process practised in Egypt. The composition of sal ammoniac being known, the process for obtaining it was improved; so that, instead of using the soot of dung, it is now formed by the distillation of bones. The impure ammoniacal liquor, thus obtained, is combined with sulphuric acid, by an easy process, and the resulting sulphate of ammonia is then decomposed by muriate of soda, by which sulphate of soda and muriate of ammonia are produced. They are separated, and the latter is formed into heads by sublimation. In this state, it occurs in commerce. It was made in great quantity in the vicinity of the temple of Jupiter Ammon; and hence its name.