2S1 



AMMONIA. 



AMMONIA. 



292 



The annexed table ahows the percentage of ammonia in aqueous 

 solutions of the gas of different specific gravities : 



The presence of ammonia may be detected by its strong odour, by 

 holding moistened turmeric paper where it is suspected to exist, and 

 by the formation of a white vapour, when exposed to a glass rod 

 moistened with hydrochloric acid. Ammonia can only thus be recog- 

 nised when it is in the free state, and therefore, in testing for. it, caustic 

 soda or quicklime should be added to the solution, in order to liberate 

 the ammonia from its combination with any acids that may be present. 



Ammonia is used for many purposes, both in medicine and in 

 scientific chemistry ; as, however, it would be impossible in some cases, 

 and inconvenient in almost every one, to employ it in its gaseous 

 state, it is used in solution in water, and then frequently called liquid 

 hi : but this term can be applied with propriety only to the gas 

 rendered fluid by cold or pressure. Solution of ammonia may be 

 readily prepared by mixing chloride of ammonium with lime, in the 

 mode and proportions already mentioned, and passing the gas liberated 

 into water : this may be done either by inserting a glass tube bent at 

 right angles into the mouth of the retort, and then putting the other 

 end into a bottle of water ; or, which is better, in case absorption 

 should take place, a tubulated receiver may be used instead of the 

 bent tube, securing it properly by a perforated cork to the retort, and 

 luting it so that it may withstand the pressure caused by passing the 

 gas into the water. Alcohol also dissolves a large quantity of ammonia. 



We shall now briefly notice the nature and results of the action of 

 ammonia upon certain elementary bodies. It has been already stated 

 that ammoniacal gas may be burned in oxygen gas : a mixture of these 

 gases may also be fired by the electric spark, the results being water 

 and nitrogen gas ; a little nitric acid is also generated, if the quantity 

 of oxygen gas be more than sufficient to combine with all the hydrogen 

 of the ammonia. (Dr. Henry, ' Phil. Trans.,' 1809.) Chlorine gas, by 

 mere admixture with ammonia, decomposes it completely, and the 

 action is attended with the evolution of light and heat. The chlorine 

 combines with the hydrogen of the ammonia ; hydrochloric acid is thus 

 formed, which uniting with the ammonia remaining undecomposed, the 

 result is chloride of ammonium, 'while nitrogen gas is liberated. The 

 same effects are obtained if the aqueous solutions of the gases in question 

 be employed ; but then the changes are unaccompanied by light or heat. 



Ammonia has no action upon carbon, except at a high temperature ; 

 if however a piece of well-dried charcoal be passed up into ammoniacal 

 er mercury, it is capable of absorbing ninety times its volume in 

 twenty-four hours. The gas undergoes no chemical change, and from 

 Saussure's experiments it appears that the absorption is analogous to 

 the capillary attraction of liquids by very small tubes. Sulphur, when 

 strongly heated in ammoniacal gas, partially decomposes it, and sulphide 

 of ammonium is one of the products. At a high temperature, phos- 

 phorus also decomposes ammonia, and phogphuretted hydrogen is 

 formed ; when no heat is employed, phosphorus absorbs the gas, and a 

 deep brown-coloured substance is formed, which is almost pulverulent : 

 its properties have not been examined. Iodine and ammonia, if put in 

 contact with water, form the well-known detonating substance iodide of 

 nitrogen, generally prepared by putting iodine into the aqueous solution 

 of ammonia. 



The action of the metals upon ammonia varies considerably, according 

 to their nature. Gay-Lussac and ThtSnard have shown that potassium 

 and sodium absorb ammoniacal gas, and are covered with a white crust. 

 The absorption i.s more rapid when the heat of a spirit-lamp is em- 

 ployed ; the white crust becomes deep yellow, the surface of the metal 

 is brilliant and smooth, whilst the new compound is greenish, fuses, 

 and runs upon the sides of the tube ; when the operation is continued 

 until the potassium entirely disappears, ammoniacal gas is not only 

 absorbed, but a portion is decomposed and hydrogen gas given out. 

 The compound formed is of a deep olive-green colour, its fracture crys- 

 talline, and its density greater than that of water. It fuses at a tempe- 

 mtiire higher than boiling water, does not conduct electricity, burns in 

 oxygen gas, and yields hydrate of potash and nitrogen gas. Water 

 decomposes it rapidly ; the results are potash and ammoniacal gas. 

 [PoTASSIUMAMIDE.] 



When .inimoiiiacal gas is passed over ignited iron or copper, the 

 density of the metals is much dimished ; and by the repeated action 

 and decom]H>sition of the gas, iron may be increased in weight, as 

 proved by Despretz, 11'5 per cent., which increase is owing to the 

 absorption of nitrogen by the metal. 



i'ii', >'/'.< "/. The general properties of the salts of ammonia 



are as follow : soluble in water, with few exceptions ; decomposed by 

 the fixed alkalies and alkaline earths, with the evolution of ammonia ; 

 decomposed when a magnesian salt and a soluble phosphate are added 

 to them, a crystalline precipitate being formed, which is a double salt, 

 composed of phosphate of ammonia and magnesia; decomposed and 

 dissipated by heat, unless the acid, like the phosphoric or boracic, be 

 a fixed one, in which ease the ammonia is expelled, and the acid remains. 

 A solution of chloride of platinum occasions a yellow precipitate in 

 concentrated solutions of ammoniacal salts. 



A few of the more important salts of ammonia are described below. 



Ammonia, Carbonates of. Several carbonates of ammonia exist ; the 

 most important are the sesquicarbonate and the bicarbonate. 



Ammonia, sesfiuicarbonate o/(2NH 4 0, 3C0 2 ). This salt is contained 

 in the Pharmacopoeia under the incorrect name of Ammonia subcarbonas, 

 or subcarbonate of ammonia. It is directed to be prepared by heating, 

 hi a subliming vessel, a mixture of one part of chloride of ammonium, 

 or sal-ammoniac, and one part and a half of carbonate of lime or chalk ; 

 it is however usually and more economically obtained by decomposing 

 sulphate of ammonia with carbonate of lime. In this case, double 

 decomposition ensues ; sesquicarbouate of ammonia is formed, volati- 

 lised, and is condensed in the upper part of the vessel, while sulphate 

 of lime remains in the lower. 



Sesquicarbonate of ammonia is a colourless, translucent, moderately 

 hard salt. It has a pungent smell, and a sharp, penetrating taste. It 

 is soluble in about four times its weight of cold water, and is decom- 

 posed by hot water. It acts upon vegetable blues and yellows, like 

 an alkali ; and on this account, as well as its ammoniacal smell, has been 

 called a subcarbonate. 



It is composed of 



Three atoms of carbonic acid . . . .66 

 Two atoms of ammonia . . ... 34 

 Two atoms of water 18 



Atomic weight 118 



As three atoms of carbonic acid are combined with two atoms of 

 ammonia, and these being as one and a half to one, this salt, like others 

 similarly constituted, is generally termed a setqnicarbonate. 



It is used in medicine as a stimulant, and usually called imelliny 

 taltt. It is also employed as a substitute for yeast in making some 

 of the finer kinds of bread. As a chemical reagent, it is extensively 

 used ; and also for preparing various other ammoniacal salts. 



Ammonia, bicarbonate of (NH.O, C0 2 + HO, C0 2 ). This salt may 

 be prepared by passing carbonic acid gas into a solution of sesquicar- 

 bonate of ammonia, in which way it may be obtained in crystals ; by 

 heating a mixture of equal weights of chloride of ammonium and car- 

 bonate of lime in a subliming vessel ; or lastly, and with the greatest 

 facility, by exposing powdered sesquicarbouate of ammonia to the air 

 until it becomes inodorous ; in this case, a larger proportion of 

 ammonia escapes than remains, and the residue thus becomes a bicar- 

 bonate. When obtained by sublimation, it resembles the sesquicar- 

 bonate in appearance, but differs from it in being devoid of pungency ; 

 it is rather hard, soluble hi cold, and decomposed by hot water. When 

 perfect, it has no alkaline action on vegetable colours, like the 

 preceding carbonates. The salt obtained by sublimation, or by 

 exposing the sesquicarbonate to the air, consists of 



Two atoms of carbonic acid . . . .44 



One atom of ammonia 17 



Two atoms of water ..... 18 



Atomic weight 



. 79 



It is rarely used, either in medicine, or as a chemical reagent. 



Ammonia, nitrate of (NH,0 NO,). A salt bestobtained by saturating 

 nitric acid with sesquicarbouate of ammonia. On evaporating the 

 solution the salt crystallises in long prisms which are anhydrous. It 

 is somewhat deliquescent, readily soluble in cold water, and when 

 heated to 480" it is decomposed into protoxide of nitrogen and water. 

 Hence its use for the preparation of protoxide of nitrogen. 



Ammonia, sulphate of (NH 4 SO^HO). A salt of ammonia pre- 

 pared on a large scale by neutralising i/as-liquvr or bmc-liijuor with 

 sulphuric acid and then crystallising. In small quantity, it is best 

 made by saturating dilute sulphuric acid with sesquicarbonate of 

 ammonia. The solution is colourless, and by evaporation yields small 

 prismatic crystals ; these have a saline taste, and are readily dissolved 

 by water. 



Crude sulphate of ammonia is largely employed in agriculture either 

 alone as a top-dressing, or as a constituent of artificial manures. It 

 powerfully stimulates the growth of cereal, grass, and root crops. 



AMMONIA, Medical jirojierties of. This alkali is distinguished 

 from the others by the appellation of Volatile, because at the ordinary 

 temperature and pressure of the atmosphere it never exists in a fixed 

 state, but either hi a gaseous form, in which case it immediately com- 

 bines with any carbonic acid which it encounters in the air, or is 

 absorbed by water or spirit, from both of which it is easily liberated, 

 jKirticularly if heat be applied. Having been formerly obtained by 

 distillation of shavings of hartshorn or other animal matters, it is 

 familiarly known under the name of Spirit of Hartshorn. The 



