AMMONIUM-SALTS. CHAPTER XXV. 437 AMMONIUM-SALTS. 519. The hypothetical metal ammonium (NH) is a device for explaining the constitution and properties of one well-defined class out of the several classes of compounds into which the gas ammonia enters. This class of compounds is that which results from neutralizing an aqueous solution of ammonia with acids, as in the following reactions : NH,HO + HSO NH,H,O + HNO = (NH,)HSO + H,O. = (NH)NO, + H20. Nitrate of Ammonium. According to this hypothesis, the crystalline salts which result from such neutralizations contain a group of atoms (NH) which is analogous in its action to potassium and sodium, and which forms salts analogous in composition to the potassium-salts. Thus chloride of ammonium (NH)Cl is analogous to chloride of potassium KC1; sulphate of ammonium (NH),SO is analogous to sulphate of potassium K,SO,, and so forth (§ 91). All the actual evidence we possess of the separate existence and metallic character of the group NH, is contained in the following curious but inconclusive experiment: Exp. 259. Pour 8 or 10 c. c. of mercury into a small flask, and warm the mercury over a gas-lamp; drop upon the mercury six or eight bits of metallic sodium, no one of them larger than a hemp-seed. The sodium dissolves with some spattering in the warm mercury, and a sodium amalgam is thus obtained. Transfer the amalgam to a tall glass or bottle of at least 300 c. c. capacity, and pour over it a concentrated solution of chloride of ammonium. The amalgam immediately begins to swell up, and ultimately increases to 8 or 10 times its original bulk, in the cold, or to 20 or 30 times if the solution be hot, assuming a pasty consistency like that of soft butter, but preserving its metallic lustre. It begins to undergo spontaneous decomposition as soon as it is formed, and if it is placed in water, this decomposition is quite rapid; 438 HYDRATE OF AMMONIUM. hydrogen gas is given off in minute bubbles, and ammonia is found in the solution. This curious substance has been supposed to be a combination of ammonium (NH) with mercury; all attempts, however, to isolate the ammonium have been unsuccessful. The proportion of ammonium (?) present in the amalgam is extremely minute, notwithstanding the great change of bulk and properties experienced by the mercury. The amalgam is said to contain only 1 part of nitrogen and hydrogen to 1800 parts of mercury. 520. Ammonium-salts are generally isomorphous with potassium-salts. They have mostly a pungent, saline taste; they are colorless, like sodium- and potassium-salts, unless the acids are colored; the carbonates, and those salts which, like the chloride and iodide, contain no oxygen, are volatile at a moderate heat without decomposition; some salts lose their ammonia when heated; if the acid which neutralized this ammonia is a nonvolatile substance, like phosphoric acid, it will remain behind undecomposed; others, like the nitrate (Exp. 34), yield simpler gases than ammonia, as, for example, nitrogen or nitrous oxide. An aqueous solution of an ammonium-salt, when exposed to the air or evaporated, generally loses ammonia and acquires an acid reaction; hence in crystallizing an ammonium-salt, ammoniawater must be occasionally added during evaporation. All ammonium-salts, whether solid or in solution, evolve ammonia when heated with the hydrates of sodium, potassium, calcium and a few other metals (Exp. 48). Exp. 260.-Warm a few centimetres of a solution of chloride of ammonium in a test-tube, add a few drops of a solution of caustic soda, and boil the liquid. The gaseous ammonia can be detected by its odor. If in any case the ammonia evolved be in so small a quantity that its characteristic smell cannot be detected, it may be recognized by its property of restoring the blue color to reddened litmus-paper (§ 83), and of forming white fumes by contact with a rod moistened with somewhat dilute chlorhydric acid (Exp. 65). The reaction may be formulated as follows: NH,C1 + NaHO = NaCl + NH, + H,O. 521. The solution of ammonia gas in water (NH,,H ̧O) may be regarded as a solution of hydrate of ammonium (NH)HO, comparable with the solution of caustic soda, NaHO, or caustic potash, KHO. This solution produces, indeed, many of the effects which CHLORIDE OF AMMONIUM. 439 the solutions of the caustic alkalies produce; it neutralizes acids, displaces the oxides of many metals from solutions of their salts, and combines with fats to form a soap; it is, in short, a powerful base. Exp. 261.-Dissolve a small crystal of alum in 6-8 c. c. of water in a test-tube, and add ammonia-water until the solution, after being well shaken, smells strongly of ammonia. A gelatinous precipitate of the hydrate of aluminum will appear in the liquid. Exp. 262.-Dissolve about 1 grm. of sulphate of zinc in 6-8 c. c. of water in a test-tube; add 4 or 5 drops of ammonia-water, and shake up the contents of the tube. A white, translucent precipitate of the hydrate of zinc will appear. Pour into the turbid liquid in the tube 3 or 4 c. c. more of ammonia-water; the precipitate will redissolve and the liquid again become clear. The zinc is at first displaced from its position in the sulphate by the group (NH4); but the hydrate of zinc thus precipitated is soluble in an excess of ammonia-water. The hydrate of ammonia behaves in this way with not a few salts of metals. Ammonium-salts are very numerous; but only the few which are of present importance in the useful arts will be here described. 522. Chloride of Ammonium (NH,Cl).-This salt, commonly called sal-ammoniac, is found native in many volcanic regions. When nitrogenized animal matter and chloride of sodium are distilled together, this salt sublimes from the mixture; the commercial supply of the salt was formerly obtained from the soot resulting from the incomplete combustion of camel's dung. The raw material whence ammonium-salts are now manufactured is derived from gasworks and boneblack-factories. Coal and bones contain a portion of nitrogen, which, during the process of distillation, is partially converted into ammonia (§ 92); this ammonia combines with the carbonic acid and sulphydric acid which are likewise products of the distillation, and these compounds are condensed into a somewhat watery liquor, contaminated with tarry and oily matters, from which the ammonium-salts are subsequently extracted. The impure carbonate is converted into chloride by the addition of chlorhydric acid, or of the mother-liquor from saltworks (a liquor containing the chlorides of magnesium and calcium); on evaporating the clarified solution, crystals of sal-ammoniac are obtained, but they are generally too dirty for use. They are partly freed from tarry matters by heating them to a temperature a little below their subliming-point, but high 440 SULPHATE OF AMMONIUM. enough to drive off the tar, and are then redissolved in water; this solution, decolorized by being filtered through animal charcoal, is recrystallized; these crystals are sometimes further purified by sublimation. Chloride of ammonium serves for the preparation of ammonia (Exp. 48), and of carbonate of ammonium. It is somewhat employed in dyeing, and also in certain processes with metals, such as tinning, soldering, and silvering copper and brass, and galvanizing (zincing) iron. The sublimed salt forms semitransparent, tough, fibrous masses; it is very soluble in water, and a great reduction of temperature occurs during its solution; hence it is employed as a refrigerant. Its taste is sharp and acrid. When heated, it sublimes much below redness, without undergoing fusion. Exp. 263.-Heat a bit of sal-ammoniac on a piece of porcelain, and observe the low temperature at which the solid is completely converted into vapor. Exp. 264.—Place a teaspoonful of powdered chloride of ammonium in the hollow of the hand, and pour upon it two or three teaspoonfuls of water. The cold produced by the solution of the salt will be very perceptible. 523. Sulphate of Ammonium ((NH),SO).—If the ammoniacal liquor from gasworks or animal-charcoal factories be neutralized with sulphuric acid, or if it be decomposed by gypsum (sulphate of calcium), the sulphate of ammonium will be obtained. In the latter case, the impure carbonate of ammonium in the liquor, on being filtered through powdered gypsum, yields carbonate of calcium and sulphate of ammonium. Another recent mode of utilizing the ammoniacal liquor of gasworks yields a crude sulphate of ammonium; the liquor is suffered to flow down the coketowers which are now often connected with sulphuric-acid chambers (§ 228), and there absorbs all the acid-fumes which escape from the chambers. A crude chloride of ammonium may be prepared in a similar way, by substituting ammoniacal liquor for water in the coke-towers of sulphate-of-sodium furnaces (§ 482). The absorbent power of the ammoniacal liquor is, of course, much greater than that of water. Sulphate of ammonium is colorless, and has a very bitter taste; it is soluble in twice its weight of cold, and in its own weight of NITRATE OF AMMONIUM. 441 boiling water. Its crystalline form is the same as that of sulphate of potassium, and the commercial article looks very much. like sand, just as the crystals of sulphate of potassium have a superficial resemblance to quartz crystals. It forms a considerable number of double salts, which are isomorphous with the corresponding salts of potassium. Sulphate of ammonium is employed in the manufacture of ammonium-alum, as an ingredient of artificial manures, and as a source of other ammonium-salts. 524. Nitrate of Ammonium ((NH)NO,).—The method of preparing this salt, and its complete decomposition by heat, have been already described (Exps. 33, 34, and § 91). The salt crystallizes in long needles; it has a pungent taste, is soluble in less than half its weight of boiling water, and in dissolving produces sharp cold. Between 230° and 250° it is decomposed into water and nitrous oxide; if it be heated hotter, or too rapidly, ammonia, nitric oxide, and nitrite of ammonium (NH)NO, are also formed. Nitrate of ammonium is formed by the action of dilute nitric acid on several metals, especially tin. 525. Carbonates of Ammonium.-Commercial carbonate of ammonium (sal-volatile) is a white, semitransparent, fibrous substance, with a pungent taste and a strong ammoniacal smell; it is prepared, on a large scale, by the dry distillation of bones, horn, and other animal matters. The product is purified from empyreumatic substances by repeated sublimation. Exp. 265.--Mix thoroughly together 10 grms. of chloride of ammonium and 20 grms. of powdered chalk; heat the mixture in a small evaporating-dish placed upon a sand-bath. When white vapors begin to rise from the hot mass, place a wide-mouthed bottle over the fuming mixture. The white sublimate which collects in the bottle is a carbonate of ammonium; chloride of calcium remains in the dish. This experiment illustrates a second, and very common, method of preparing the commercial carbonate, which simply consists in heating to redness a mixture of 1 part of chloride, or sulphate, of ammonium and 2 parts of carbonate of calcium. When this commercial carbonate is dissolved in strong ammonia-water at about 30°, a solution is obtained which yields large, transparent, prismatic crystals. These crystals, however, have no stability; they are rapidly decomposed in the air, giving off water and |