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    "source_title": "Encyclopaedia Britannica (1926)",
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    "title": "AMMONIA",
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    "verified_text": "the production of ammonia andammo- nium salts increased during the war pcriod, due to the direct use of ammonium nitrate and, to a lesser extent, perchlorate, as mix- tures for shell filling, and to the demand for nitrogenous fer- tilisers. attention was also directed to the combustion of ammo- nia as a source of nitric acid and nitrates, and to the production of urea from ammonia and carbon dioxide. in obtaining ammonia and its compounds from the ammo- niacal liquors of gas works and coke-oven recovery plant, con- tinuous stills are usually worked in such a manner that the pre- heated ammoniacal liquor passes down a column: similar in function to the columns of spirit or benzole stills, in which it meets an upward current of steam. the salts of ammonia with weak volatile acids are thereby dissociated and the ammonia, mixed with carbon dioxide, hydrogen sulphide, etc. usually passes into saturators containing sulphuric acid, where it is converted intogammonium sulphate. the remainder of the ammonium salts, which are not readily dissociated, react with heated milk of lime in a still at the base of the column, the remainder of the ammonia being expelled and subsequently converted for the most part into ammonium sulphate. ammonia obtained from gas works or coke-oven recovery plant, or from salts derived from this source, is usually con- taminated with small quantities of pyridine bases. it is advis- able to use synthetic ammonia when a high degree of purity of the ammonia is essential. in attempting, like stas, to purify ammonium salts by treatment with oxidising agents, the resist- ance of the pyridine ring to oxidation should be kept in mind. compounds with acids —whilst ammonium salts of weak acids are easily dissociated on heating in aqueous solution, the salts with strong acids are more stable but nevertheless lose some of their ammonia on boiling. veley (1905) measured the degree of hydrolysis by boiling a definite volume of a salt solution con- taining a known amount of the salt for a definite time and deter- mining the loss of ammonia. e. g. hill vour. chem. soc., 1906, vol. 89, p. 1273), by further experiments with greater refinement, showed that for monobasic acids the hydrolytic dissociation is inversely proportional to the “strength” of the acid. ammonium perchlorate —this salt may be obtained from an alka- line perchlorate, obtained electrolytically, and an ammonium salt. its use in high explosive shell is limited owing to the liability to detonation by mechanical shock. ammonium thiocyanate.—this can be obtained from ammonia and carbon disulphide, cs.+4nh3=nh,cns+(nh2)2s. in addi- tion to other uses, its isomerisation to thiocarbamide, cs(nh,)s, has become of interest in relation to the rubber industry. solutions of ammonia in water apparently contain ammonium hydroxide, nh,oh, in very small amount. an equilibrium exists in the solution which may be expressed by the combined equation nh;+h.0 pls nh, oh ra nh,-+oh’ which is not intended to exclude the formation of complexes (nh3)m(h20)2. accepting bredig’s value for the velocity of the am- monium ion (70-4 at 25°) and assuming that nhj and oh’ are the only ions existing in the aqueous solution, it appears that of the total ammonia approximately the following amounts are ionised: n/100, 4%; n/lo, rather over 1%; n/1, about o-3-0-4%. information as 1 the synthetical production of ammonia is dealt with under nitrogen, fixation of. ammonia to the form in which ammonia exists in aqueous solution is given by hantzsch and sebaldt, and t. s. moore. the definite, though small, electric conductivity of liquefied ammonia points to the existence of ions which may be nh,’, nii’, n’” and niu, the latter from the union of ammonia with hydrion. the dielectric constant of ammonia is 21 to 23, many salts dis- solve in liquefied ammonia giving electrically conducting solutions, the conductivity is far inferior to that of the corresponding aqueous solutions, thus 1 mol of potassium itodide is ionised to the extent of go°%, if dissolved in 20 litres of water but requires 2,000 litres of ammonia for an equal degree of ionic dissociation. the limiting value of ionisation of a salt is usually reached at 1,000 to 5,000 litres in the case of water and at 25,000 to §0,000 litres in the case of ammonia. | constitution of ammonium salis—the former view was that when ammonia combined with an acid, the tervalent nitrogen atom became quinquevalent. werner thought that subsidiary valencies are called into play, representing, e.g., ammonium chloride in the following manner :— . ortyen yeuce 2d ed but ammonia also combines with the alkyl esters of strong acids, thus the first product of the action of ethyl chloride on ammonia is ethylammonium chloride, n(c.hs;)1i;c:. since alkalies liberate ethylamine, n(cofi;)he, from this salt, the assumption has to be made that the additional ammonium salt undergoes intramolecular change in its kation chs ¢.«.4- ry sgn roo ~ )s the formation of di-, tri-, and tetra-alkyl ammonium salts by successive replacement of hydrogen by alkyl is explained similarly. whilst the ionisable acid radicle can be readily accepted as standing outside the rest (kationic portion) of the molecule, non- equivalence of the four valencies binding alkyl groups is difficult to imagine. a quaternary ammonium salt, in which all four alkyl groups are different, does not exhibit isomerism if the groups are introduced in different order. moreover, if a salt or hydroxide be decomposed by heat, the alkyl group which escapes with acid radicle or hydroxyl depends on the nature of the group and not on the order in which it has been introduced into the molecule. the firm attachment of the alkyl groups to the nitrogen atom is attested by the fact that quaternary ammonium bases are only liberated from their salts by the action of bases which form in- soluble salts with the kations; e.g., moist silver oxide in the case of the halides, barium hydroxide in the case of the sulphates. the stability of the quaternary ammonium grouping is illus- trated by the amalgam obtained when an absolute alcoholic solution of tetramethylammonium chloride is electrolysed with a mercury kathode (mccoy and moore, jour. amer. chem. soc., iqi1, vol. 33, p. 273). the amalgam has a crystalline fracture and differs from ammonium amalgam in not becoming inflated below to°c, in contact with air it becomes coated with an alkaline crust, it decomposes water with evolution of hydrogen and forma- tion of colloidal mercury and tetramethylammonium hydroxide. when all four alkyl groups of a quaternary ammonium salt are different, the compound can be resolved into optical isomerides. pope and peachey (jour. chem. soc., 1899, vol. 75, p. 1127) definitely resolved benzylphenylallylmethylammonium salts into dextro- and laevo-rotatory forms, experiments by le bel (compt. rend., 1891, vol. 112, p. 724) had not been conclusive. the probability that the four alkyl groups are arranged at the corners of a tetrahedron with the nitrogen atom at the centre has been made certain by the resolution of 4-phenyl-4! carbethoxypipe- ndinium-1:1'-spiran bromide into its enantiomerides (mills and warren, jour. chem. soc., 1925, vol. 127, p. 2507). on the electronic theory, it is probable that the ammonium ion, nhj, and the methane molecule, ch,, have corresponding configu- rations since each complex is composed of a positive nucleus, four hydrogen nuclei, and ten electrons, this is confirmed by the experimental stereochemical evidence. ammonia and metallic salis—ammonia reacts with metallic salts in different ways. either hydrogen in the metallic salt is replaced by metal or addition takes place. besides the amides (or nitrides) of the alkali and alkaline earth metals, e.g., soda- mide, nan ha, obtained by the direct action of sodium on ammonia with liberation of hydrogen, compounds are known which may be regarded as ammonium salts in which hydrogen has been ammunition ee 3 replaced by metal. thus “ infusible white precipitate ’’ may be mercuriammonium chloride, nu.ngcl, though possibly it is mercuric amide chloride, hg(nh2)cl. the latter structure may be compared with that of zinc diamide, zn(n h2)}2, a stable com- pound obtained by the action of ammonia on ethereal solution of zinc ethide (frankland, 1858). an amide-halide structure, nh.-<{fg-i, seems to be necessary for the substance produced with liberation of ethane by the action of ammonia on an ethereal solution of ethylmagnesium iodide (oddo and calderaro). co-ordination compounds. —when ammonia is directly attached to a metallic salt, it is convenient to introduce werner’s idea of co- ordination. this_ may be illustrated by reference to quadrivalent platinum, whose chloride, ptch, is a non-electrolyte. with two molecules of potassium chloride, we have potassium platinichloride, koptch. in hexammine- platinic chloride, ptch,6nhz2, all four chlorine atoms are ionisable, the complex [pts on hs] forming a quadrivalent kation. c ompounds with intermediate ‘proportions of ammonia are known, but in every case the sum of the atoms and ammo- nia molecules intimately associated with the platinum atom is six, the co-ordination number. other atoms belonging to the molec ule are ionisable as seen in the following list :— [ptcl.]ks, gives the ions [ptclj\"* and 2k\" [ptcl:,niis]k, gives the ions [ptcl;,nh,]' and k° [ptcl,2nh)3], is a non-electrolyte [ptcls, 3ni lich, gives the ions [ptcl;,3nh:]\" and cl’ [ptcl,4nhz)ch, gives the ions [ptch,4nbh) and 2c} [pt,6nh,]jch, gives the ions [pt,6nh,]\"\" » and 4cl’ many complex compounds of chromium, iron, nickel and cobalt are known in which the metal exhibits the co- -ordination number 6, but in the case of divalent platinum and copper, the co- -ordination number is four. thus two non-ionisable compounds of the formula pt(nh3)2cl are known, their isomerism may be explained if we suppose the platinum atom to be situated at the centre of a square of which the corners represent the positions occupied by chlorine or ammonia, cl cl cl nh; a ; nh; nhs nh; cl biibliography.—a. werner, berichte der deutschen chemitschen gesellschaft (1912); sir h. e. roscoe and c. schorlemmer, treatise on chemistry (1920); t. e. thorpe, dictionary of applied chemistry, vol. 1. (1921); g. lunge, coal tar and ammonia, pt. iiif. (1916); p. parrish, design and working of ammonia stills (1924); a, rogers, manual of industrial chemistry (4th ed., 1925). (j. th)",
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