Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/522

Rh 510 CHEMISTRY [AMMONIA. from its elements by submitting a mixture of the two gases to the action of the silent electric discharge; the combination is very imperfect, however. It is also obtained by the action of nascent hydrogen on nitric acid and many of its salts ; but it is always prepared by heating an ammonium salt with an alkaline hydroxide, ammonium chloride and calcium hydroxide or slaked lime being the substances which are usually employed Ca(OH) 2 = 2NH 3 + 20H 2 + CaCl 2. Calcium &quot;. Calcium hydroxide. chloride. 2NH 4 C1 Ammonium chloride. Ammonia is a product of the decay of all nitrogenous animal and vegetable substances, and the ammonia present in the atmosphere is chiefly if not entirely derived from this source ; but it appears not improbable that ammonia is directly produced in the atmosphere by the decomposi tion of water into its elements by the electric discharge, and the combination also under the influence of the dis charge of the hydrogen thus produced with nitrogen. Am monia is present in the atmosphere apparently as car bonate, and in rain-water, especially in that of thunder showers, as nitrate and nitrite. Ammonia salts are sometimes found as minerals, chiefly in volcanic districts. The source from which ammonia salts are now obtained, however, is the watery liquid which distils over in the manufacture of coal gas ; the ammonia is liberated from this liquid by heating it with slaked lime, and by receiving it in sulphuric acid ammonium sulphate is pro duced, a salt which is largely employed as an artificial manure. Ammonia is a transparent colourless gas, of a very pungent peculiar odour, and a burning taste. It may be reduced to the liquid state by a pressure of about 17 atmospheres at the ordinary temperature, or by cold alone at about - 50 to - 40 C. ; by exposing the dry gas to a cold of 75 C. and a pressure of 20 atmospheres, Faraday obtained ammonia as a white transparent crystal line body, melting at 75 C. It does not support com bustion, and is only feebly combustible. It is decomposed into its elements by a succession of electric sparks. Ammonia is dissolved by water with great avidity, much heat being developed and great expansion taking place ; according to Roscoe and Dittmar, 1 gramme of water at C. dissolves no less than 875 gramme of ammonia. The solution has the smell and taste of the gas, and a powerfully alkaline reaction ; it loses almost all its ammonia below 100 C. Ammonia completely neutralizes acids, forming definite crystalline salts, known as ammonium salts, which are formed by the direct combination of ammonia with the acids ; ammonia and hydrochloric acid, for example, form ammonium chloride, NH 4 C1 = NH 3 + HC1, whilst ammonia and sulphuric acid furnish ammonium sulphate, (NH 4 ).,SO 4 = 2NH 3 + H 2 S0 4. The constitution of these salts, it will be evident, is analogous to that of the salts of the metals generally if we regard them as derived from the acids by the displacement of the hydrogen of the latter by the monad compound radicle ammonium, NH 4, and this view is confirmed by the observation that the ammonium salts are isomorphous with the corresponding potassium salts. They are all soluble in water, and are readily decomposed by the alkaline hydroxides, and by most basic oxides, with evolution of ammonia. The solution of ammonia in water is frequently regarded as the hydroxide of the hypothetical radicle ammonium, that is to say, as a solution of ammonium hydroxide, NH 4 .OH, the analogue of potassium hydroxide, KOH. But Thomsen has shown that considerably less heat is de veloped when an acid is neutralized by a solution of ammonia than when it is neutralized by a solution of an alkaline hydroxide, such as potassium hydroxide, for example, the reaction KHOAq, HClAq being accompanied by the development of 27,500 units of heat, whilst only 24,500 are developed in the reaction NH 3 Aq, HClAq. Thomsen is inclined to regard this result as evidence that ammonia exists as such in its aqueous solution, and not as the hydroxide NH 4 .OH, but the difference observed appears scarcely sufficient to warrant this conclusion iu the face of the chemical evidence which points to the existence of an ammonium hydroxide ; it is more probable, perhaps, that an aqueous solution of ammonia consists in part of the hydroxide and in part of free ammonia. A very large number of derivatives may be obtained from ammonia by displacing one or more atoms of hydro gen in it by positive or negative radicles. Those which are formed by the introduction of monad positive radicles are distinguished by the name amines, whilst those con taining monad negative radicles are called amides ; when two atoms of hydrogen in a single molecule of ammonia are displaced by dyad negative radicles so-called imides are produced. A simple instance of the formation of an amine derivative is afforded by the action which takes place when potassium is heated in an atmosphere of ammonia 2NH 3 Ammonia. 2K = 2NH 2 K Fotassamine. H By digesting iodine in an excess of aqueous ammonia a black explosive compound is produced, which apparently is formed by the displacement of two of the atoms of hydrogen by iodine 3NH 3 Ammonia. 2I 2 = NHI 2 Diiodamide. 2NH 4 I. It may be exploded by friction even under water, and in tho dry state can scarcely be touched without exploding. When chlorine is passed into an aqueous solution of ammonia, nitrogen is evolved and ammonium chloride is produced ; thus + 3C1 2 = N 2 + 6NH 4 C1. If the action of the chlorine be continued after the whole of the ammonia is thus acted upon, the ammonium chloride becomes attacked, and yellow oily drops of the so-called chloride of nitrogen are formed. The composi tion of this substance has not yet been satisfactorily ascertained ; it probably contains hydrogen, and its for mula is supposed to be NHC1 2, but it is not unlikely that the compound NC1 3 is also produced. It explodes with extreme violence when heated, or when brought in contact with fatty matters, or with turpentine, phosphorus, and many other substances. The Oxides and Acids of Nitrogen. No less than five oxides of nitrogen are known, viz. N 2 ; NO ; N 2 3 ; N 2 4 ; N 2 O 5. Nitrous Nitric Nitrous Nitric Nitric oxide. oxide anhydride. peroxide. anhydride. Nitrous and nitric oxide are merely dissolved by water, but the remaining oxides enter into reaction with it, producing acids, nitrous and nitric anhydride being converted into the corresponding acids, nitrous and nitric acid, and a mixture of those two acids being formed from the intermediate oxide, nitric peroxide ; thus N 2 3 + H 2 = 2HN0 2 Nitrous anhydride. Nitruus acid. N 2 O 4 + H 2 = HN0 2 + HN0 3 Nitric peroxide. Nitrous acid. Nitric acid. N 2 5 + H 2 = 2HN0 3 Nitric anhydride. Nitric acid. As these various oxides of nitrogen are all prepared from nitric acid, we may conveniently describe this compound first.