_Estim._ The quantity of gaseous ammonia in pure water of ammonia is easily determined from the specific gravity of the liquid, or from its saturating power. When impure or mixed with other substances, a given weight of the sample is placed in a small retort, the end of which is made to dip into a vessel containing dilute hydrochloric acid. A strong solution of caustic potassa is then poured into the retort, and heat applied by means of a small spirit lamp. When _all_ the ammonia is distilled over, the acid solution is evaporated to dryness, by the heat of a water bath, and the residuum (chloride of ammonium) weighed. Each grain of the chloride thus found represents ·31804 gr. of pure ammonia; 53·5 parts of the former being equivalent to 17 of the latter. If the article for examination be a solid substance (as a salt), it may be dissolved in water, or in dilute acid, before being put into the retort. In accurate experiments in the laboratory, ammonia is usually WEIGHED either as chloride of ammonium (see _above_), or as ammonio-bichloride of platinum (NH_{4}Cl, PtCl_{2}); every gr. of the latter representing ·07614 gr. of pure ammonia. Sometimes, though rarely, the quantity of ammonia is determined from the volume of nitrogen eliminated from it, of which 14 gr. represent 17 gr. of ammonia. _Concluding remarks, Patents, &c._ Whatever form or process may be adopted for the preparation of liquid ammonia, it is absolutely necessary to keep the receivers as cool as possible, by means of snow, ice, or a current of very cold water, for the purpose of promoting the absorption of the gas, and to prevent its loss. On the small scale, the glass receivers or bottles may be most conveniently surrounded with ice, or a freezing mixture, and two, or more of them, should be furnished with safety-tubes, to prevent accidents. On the large scale, a capacious oblong retort, usually of iron (but sometimes, though seldom, of lead), with a large opening or tubulature conveniently situated for inserting the ‘charges,’ and withdrawing the residuum of the distillation, is employed. The tubulature, or opening, is closed by means of a large and accurately ground iron stopper, or with a door secured by screws, as the case might be. The stopper is well greased before insertion, and is removed by means of a powerful lever. Should it become so firmly fixed that it cannot be displaced in the usual manner, a cloth moistened with cold water, and carefully wrapped round it, without touching the neck of the retort, will generally cause it to contract sufficiently to enable the operator to remove it with facility. Sometimes a large iron kettle, with a moveable and accurately fitting lid secured in its place like that of a ‘Papin’s digester,’ and having a large and long tubulature in its centre, is employed instead of a retort, over which it has the advantage of exposing a larger opening for the removal of the residuum of the process. In either