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AMMONIA (NH3)

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Originally appearing in Volume V01, Page 863 of the 1911 Encyclopedia Britannica.
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AMMONIA (NH3) . Salts of ammonia have been known from very See also:early times'; thus the See also:term Hammoniacus sal appears in the writings of See also:Pliny (Nat. Hist. xxxi. 39), although it is not known whether the term is identical with the more See also:modern sal-ammoniac (q.v.). In the See also:form of sal-ammoniac, ammonia was known, how-ever, to the alchemists as early as the 13th See also:century, being mentioned by Albertus See also:Magnus, whilst in the 15th century See also:Basil Valentint showed that ammonia could be obtained by the See also:action of alkalies on sal-ammoniac. At a later See also:period when sal-ammoniac was obtained by distilling the hoofs and horns of oxen, and neutralizing the resulting carbonate with hydrochloric See also:acid, the name See also:spirits of See also:hartshorn was applied to ammonia. Gaseous ammonia was first isolated by J. See also:Priestley in 1774 and was termed by him " alkaline See also:air.", In 1777 K. W. See also:Scheele showed that it contained See also:nitrogen, and C. L. Berthollet, in about 1785, ascertained its See also:composition.

Ammonia is found in small quantities as the carbonate in the See also:

atmosphere, being produced from the putrefaction of nitrogenousanimal and See also:vegetable See also:matter; ammonium salts are also found in small quantities in. See also:rain-See also:water,. whilst ammonium chloride (sal-ammoniac) and ammonium sulphate are found in volcanic districts; and crystals of ammonium bicarbonate have been found in Patagonian See also:guano. Ammonium salts too are found distributed through all fertile See also:soil, in See also:sea-water, and in most plant and See also:animal liquids, and also in urine. Ammonia can be synthesized by submitting a mixture of nitrogen and See also:hydrogen to the action of the silent electric See also:discharge, the See also:combination, however, being very imperfect. It is obtained by the dry See also:distillation of nitrogenous vegetable and animal products; by the reduction of nitrous acid and nitrites with nascent hydrogen; and also by the decomposition of ammonium salts by alkaline hydroxides or by slaked See also:lime, the See also:salt most generally used being the chloride (sal-ammoniac, q.v.) thus 2NH4C1+Ca(OH)2= CaC12+2H2O+2NH3. It also results on decomposing See also:magnesium nitride (Mg3N2) with water, Mg3N2 + 61120 = 3Mg(OH)2 + 2NH3. Large quantities of ammonia and ammonium salts are now obtained from the ammoniacal liquor of See also:gas-See also:works. Ammonia is a colourless gas possessing a characteristic pungent See also:smell and a strongly alkaline reaction; it is lighter than air, its specific gravity being o• 589 (air= I). It is easily liquefied and the liquid boils at — 33.7° C., and solidifies at — 7 5° C. to a See also:mass of See also:white crystals. It is extremely soluble in water, one See also:volume of water at o° C. and normal pressure absorbs 1148 volumes of ammonia (See also:Roscoe and W. Dittmar). All the ammonia contained in an aqueous See also:solution of the gas may be expelled by boiling. It does not support See also:combustion; and it does not See also:burn readily unless mixed with See also:oxygen, when it See also:burns with a See also:pale yellowish-See also:green See also:flame.

Ammonia gas has the See also:

power of combining with many substances, particularly with metallic halides; thus with See also:calcium chloride it forms the See also:compound CaCl2.8NH3, and consequently calcium chloride cannot be used for drying the gas. With See also:silver chloride it forms two compounds (F. Isambert, Comptes rendus, 1868, lxvi. p. 1259)—one, AgC1.3NH3 at temperatures below 15° C.; the other, 2AgC1.3NHt at temperatures above 2o° C. On See also:heating these substances, ammonia is liberated and the metallic chloride remains. It was by the use of silver chloride ammonia compounds that in 1823 M. See also:Faraday was first able to liquefy ammonia. It can be shown by Isambert's results that the compound AgCI.3NH3 cannot be formed above 2o° C., by the action of ammonia on silver chloride at atmospheric pressure; whilst 2AgC1.3NH3; under similar conditions, cannot be formed above about 68° C. Liquid ammonia is used for the artificial preparation of See also:ice. It readily dissolves See also:sodium and See also:potassium, giving in each See also:case a dark See also:blue solution. At a red See also:heat ammonia is easily decomposed into its constituent elements, a similar decomposition being brought about by the passage of electric See also:sparks through the gas. See also:Chlorine takes See also:fire when passed into ammonia, nitrogen and hydrochloric acid being formed; and unless the ammonia be See also:present in excess, the highly explosive nitrogen chloride NCI; is also produced.

With See also:

iodine it reacts to form nitrogen iodide. This compound was discovered in 1812 by See also:Bernard See also:Courtois, and was originally supposed to contain nitrogen and iodine only, but in 184o R.F.Marchand showed that it contained hydrogen, whilst R. See also:Bunsen showed that no oxygen was present. As regards its constitution, it has been given at different times the formulae NI3, NHI,,: NH2I, N2H,I3, &c., these varying results being due to the impurities in the substance, owing to the different investigators working under unsuitable conditions, and also to the decomposing action of See also:light. F. D. Chattaway determined its composition as N2H3I3, by the addition of excess of See also:standard sodium sulphite solution, in the dark, and subsequent titration of the excess of the sulphite with standard iodine. The constitution has been definitely determined by 0. Silberrad (Jour. of Chem. See also:Soc., 1905, Ixxxvii. p. 55) by the interaction of nitrogen iodide with See also:zinc See also:ethyl, the products of the reaction being triethylamine and ammonia; the 'ammonia liberated . was absorbed in hydrochloric acid, and 95 % of the theoretical amount of the ammonium chloride was obtained. On these grounds O.

Silberrad assigns the See also:

formula NH3•NI3 to the compound and explains the decomposition as taking See also:place, 2NH3•NI3+ 6Zn(C2H5)2= 6ZnC2H5•I+2NH3d-2N(C2H5)3. The hydrogen in ammonia is capable of replacement by metals, thus magnesium burns in the gas with the formation of magnesium nitride Mg3N2, and when the gas is passed over heated sodium or potassium, sodamide, NaNH2, and potassamide, KNH2, are formed. One of the most characteristic properties of ammonia is its power of combining directly with acids to form salts; thus with hydrochloric acid it forms ammonium chloride (sal-ammoniac); with nitric acid, ammonium nitrate, &c. It is to be noted that H. B. See also:Baker (See also:Journal of Chem. Soc., 1894, lxv. p. 612) has shown that perfectly dry ammonia will not combine with perfectly dry hydrochloric acid, moisture being necessary to bring about the reaction. The aqueous solution of ammonia is very basic in its reactions, and since it is a weak electrolyte, one must assume the solution to contain a certain amount of ammonium hydroxide NH4OH, although it is probably chiefly composed of a solution of ammonia in water. (On the constitution of aqueous ammonia solutions see also Carl Frenzel, Zeit fitr angew. Chemie, xxxii. 3, p.

319.) Ammonia finds a wide application in organic See also:

chemistry as a synthetic reagent; it reacts with alkyl iodides to form See also:amines (q.v.), with See also:esters to form acid amides (q.v.), with halogen fatty acids to form amino-acids; while it also combines with isocyanic esters to form alkyl ureas and with the See also:mustard See also:oils to form alkyl thioureas. See also:Aldehydes also combine directly with ammonia. Liquid ammonia possesses strong ionizing See also:powers, and solutions of salts in liquid ammonia have been much studied. For details see E. C. See also:Franklin and C. A. Kraus, Amer. Chem. Jour., 1899, xxi. p. 8; 'goo, See also:xxiv. p. 83; 1902, See also:xxviii. p.

277; also Carl Frenzel, Zeits See also:

fur Elektrochemie, 1900, vi. p. 477. The salts produced by the action of ammonia on acids are known as the ammonium salts and all contain the compound See also:radical ammonium (NH4). Numerous attempts have been made to isolate this radical, but so far none have been successful. By the addition of sodium See also:amalgam to a concentrated solution of ammonium chloride, the so-called ammonium amalgam is obtained as a spongy mass which floats on the See also:surface of the liquid; it decomposes readily at See also:ordinary temperatures into ammonia and hydrogen; it does not reduce silver and See also:gold salts, a behaviour which distinguishes it from the amalgams of the See also:alkali metals, and for this See also:reason it is regarded by some chemists as being merely See also:mercury inflated by gaseous ammonia and hydrogen. M. le See also:Blanc has shown, however, that the effect of ammonium amalgam on the magnitude of polarization of a See also:battery is comparable with that of the amalgams of the alkali metals. Many of the ammonium salts are made from the ammoniacal liquor of gas-works, by heating it with See also:milk of lime and then absorbing the gas so liberated in a suitable acid. (See Gas: Manufacture.) Ammonium bromide, NH4Br, can be prepared by the See also:direct action of See also:bromine on ammonia. It crystallizes in colourless prisms, possessing a saline See also:taste; it sublimes on heating and is easily soluble in water. On exposure to air it gradually assumes a yellow See also:colour and becomes acid in its reaction. Ammonium chloride, NH4C1. (See SAL-AMMONIAC.) Ammonium fluoride, NH4F, may be obtained by neutralizing ammonia with hydrofluoric acid.

It crystallizes in small prisms, having a See also:

sharp saline taste, and is exceedingly soluble in water. It decomposes silicates on being heated with them. Ammonium iodide, NH4I, can be prepared by the action of hydriodic acid on ammonia. It is easily soluble in water, from which it crystallizes in cubes, and also in See also:alcohol. It gradually turns yellow on See also:standing in moist air, owing to decomposition with liberation of iodine. Ammonium chlorate, NH4C1O3, is obtained by neutralizing chloric acid with either ammonia or ammonium carbonate, or by precipitating See also:barium, See also:strontium or calcium See also:chlorates with ammonium carbonate. It crystallizes in small needles, which are readily soluble in water, and on heating, decompose at about 102 C., with liberation of nitrogen, chlorine and oxygen. It is Soluble in dilute aqueous alcohol, but insoluble in strong alcohol. Ammonium See also:carbonates. The commercial salt is known as sal-volatile or salt of hartshorn and was formerly obtained by the dry distillation of nitrogenous organic matter such as See also:hair, See also:horn, decomposed urine, &c., but is now obtained by heating a mixture of sal-ammoniac, or ammonium sulphate and See also:chalk, to redness in See also:iron retorts, the vapours being condensed in leaden receivers. The crude product is refined by sublimation, when it is obtained as a white fibrous mass, which consists of a mixture of hydrogen ammonium carbonate, NH4-HCO3, and ammonium carbamate, NH2COONH4, in molecular proportions; on See also:account of its possessing this constitution it is sometimes called ammonium sesquicarbonate. It possesses a strong ammoniacal smell, and on digestion with alcohol the carbamate is dissolved and a See also:residue of ammonium bicarbonate is See also:left; a similar decomposition taking place when the sesquicarbonate is exposed to air.

Ammonia gas passed into a strong aqueous solution of the sesquicarbonate converts it into normal ammonium carbonate, (NH4)2CO3, which can be obtained in the crystalline See also:

condition from a solution prepared at about 3o° C. This compound on exposure to air gives off ammonia and passes back to ammonium bicarbonate. Ammonium bicarbonate, NH4•HCO3, is formed as shown above and also by passing See also:carbon dioxide through a solution of the normal compound, when it is deposited as a white See also:powder, which has no smell and is only slightly soluble in water. The aqueous solution of this salt liberates carbon dioxide on exposure to air or on heating, and becomes alkaline in reaction. The aqueous solutions of all the carbonates when boiled undergo decomposition with liberation of ammonia and of carbon dioxide. Ammonium nitrate, NH4NO3, is prepared by neutralizing nitric acid with ammonia, or ammonium carbonate, or by See also:double decomposition between potassium nitrate and ammonium sulphate. It can be obtained in three different crystalline forms, the transition points of which are 350 C., 83° C. and 125° C. It is easily soluble in water, a considerable lowering of temperature taking place during the operation; on this account it is sometimes used in the preparation of freezing mixtures. On See also:gentle heating, it is decomposed into water and nitrous See also:oxide. P. E. M.

See also:

Berthelot in 1883 showed that if ammonium nitrate be rapidly heated the following reaction takes place with explosive violence :—2NH4NO3 = 41120+2N2+02. Ammonium nitrite, NH4NO2, is formed by oxidizing ammonia with See also:ozone or hydrogen peroxide; by precipitating barium or See also:lead nitrites with ammonium sulphate, or silver nitrite with ammonium chloride. The precipitate is filtered off and the solution concentrated. It forms colourless crystals which are soluble in water and decompose on heating, with the formation of nitrogen. Ammonium See also:phosphates. The normal phosphate, (NH4)3PO4,is obtained as a crystalline powder, on mixing concentrated solutions of ammonia and phosphoric acid, or on the addition of excess of ammonia to the acid phosphate (NH4)2HPO4. It is soluble in water, and the aqueous solution on boiling loses ammonia and the acid phosphate NH4H2PO4 is formed. Diammonium hydrogen phosphate, (NH4)2HPO4, is formed by evaporating a solution of phosphoric acid with excess of ammonia: It crystallizes in large transparent prisms, which melt on heating and decompose, leaving a residue of metaphosphoric acid, (HPO3). Ammonium dihydrogen phosphate, NH4•H2PO4, is formed when a solution of phosphoric acid is added to ammonia until the solution is distinctly acid. It crystallizes in quadratic prisms. Ammonium sodium hydrogen phosphate, NH4•NaHPO4.4H2O. (See MICROCOSMIC SALT.) Ammonium sulphate (NH4)2SO4 is prepared commercially from the ammoniacal liquor of gas-works (see Gas: Manufacture) and is purified by recrystallization.

It forms large rhombic prisms, has a somewhat saline taste and is easily soluble in water. The aqueous solution on boiling loses some ammonia and forms an acid sulphate. It is used largely as an artificial manure, and also for the preparation of other ammonium salts. Ammonium persulphate (NH4)2S203 has been prepared by H. See also:

Marshall (Jour. of Chem. Soc., 1891, lix. p. 777) by the method used for the preparation of the corresponding potassium salt (see See also:SULPHUR). Pure specimens are difficult to obtain. It is very soluble in See also:cold water, a large fall of temperature accompanying solution. Ammonium sulphide, (NH4)2S, is obtained, in the form of micaceous crystals, by passing sulphuretted hydrogen mixed with a slight excess of ammonia through a well-cooled See also:vessel; the hydrosulphide NH4.HS is formed at the same See also:time. It dissolves readily in water, but is probably partially dissociated in solution. The hydrosulphide NH4•HS can be obtained as a white solid, by mixing well-cooled ammonia with a slight excess of sulphuretted hydrogen.

According to W. P. Bloxam (Jour. of Chem. Soc., 1895, lxvii. p. 283), if sulphuretted hydrogen is passed into strong aqueous ammonia at ordinary temperature, the compound (NH4)2S.2NH4HS is obtained, which, on cooling to o° C. and passing more sulphuretted hydrogen, forms the compound (NH4)2S• 12NH4HS. An ice-cold solution of this substance kept at o° C. and having sulphuretted hydrogen continually passed through it gives the hydrosulphide. Several complex poly-sulphides of ammonium have been isolated, for details of which see Bloxam's See also:

paper quoted above. Compounds are known which may be looked upon as derived from ammonia by the replacement of its hydrogen by the sulpho-See also:group (HSO3); thus potassium See also:ammon-trisulphonate,N(SO3K)3.2H20,is obtained as a crystalline precipitate on the addition of excess of potassium sulphite to a solution of potassium nitrite, See also:KNO2+3K2SO3+2H20= N(SO3K)3 +4KHO. It can be recrystallized by solution in alkalies. On boiling with water, it is converted, first into the disulphonate NH(SO3K)2 thus, N(SO3K)3+H20=NH(SO3K)2+KHSO4, and ultimately into the monosulphonate NH2•SO3K. The disulphonate is more readily obtained by moistening the nitrilosulphonate with dilute sulphuric acid and letting it stand for twenty-four See also:hours, after which it is recrystallized from dilute ammonia. It forms monosymmetric crystals which by boiling with water yield amidosulphonic acid.

(See also E. See also:

Divers, Jour. of Chem. Soc., 1892, lxi. p. 943.) Amidosulphonic acid crystallizes in prisms, slightly soluble in water, and is a See also:stable compound. Ammonia and ammonium salts can be readily detected, in very See also:minute traces, by the addition of Nessler's solution, which gives a distinct yellow coloration in the presence of the least trace of ammonia or ammonium salts. Larger quantities can be detected by warming the salts with a See also:caustic alkali or with quicklime, when the characteristic smell of ammonia will be at once apparent. The amount of ammonia in ammonium salts can be estimated quantitatively by distillation of the salts with sodium or potassium hydroxide, the ammonia evolved being absorbed in a known volume of standard sulphuric acid and the excess of acid then determined volumetrically; or the ammonia may be absorbed in hydrochloric acid and the ammonium chloride so formed precipitated as ammonium chlorplatinate, (NH4)2PtC16.

End of Article: AMMONIA (NH3)

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