Modern Gasworks Practice

504 MODERN GASWORKS PRACTICE It does not follow that gas liquor will contain. every one of the above salts ; in fact, some of those included are only met with on rare occasions. Ammonium car'bania'tG, is deposited as a whitc solid. wJicn COa ancl annnonia meet. It is easily soluble in water, but is probably present in only minute quantities in gas liquor, for, when dissolved, it is soon converted into carbonate. As regards the “ fixed ” salts, fliese are largely accounted for by ammonium chloride, which. owes its presence to the common salt (sodium chloride) present in the original coal. The amount of salt varies considerably according to the dass of coal used, the maxi-niu.ro. proportion in the coal being about 0'25 per cent. Auimonium chloride is a particularly unwelcome compound, for, in addition to its deleterious eflects on the fireclay of the retorts,1 it bas—in the gaseous state—a marked corrosive action on the steelwork of the hydraulic main, etc. When deposited in the solid state it may give rise to considerable trouble, due to the stoppage of pipes, and in some cases special means have been introduced for dealing with it.2 Ammonium cyanide is present only in traces, and is frequently absent altogetlier. The ferrocyanide is also of rare occurrence, so much so that, during an examination. of various liquors extending over a period of five years, conducted by the chief inspector under the Alkali Act, it was only identified with certainty on one occasion. Ammoniacal liquor is considerably afiected by oxidation, so that its ultimate constituents are influenced in some degree by the amount of oxygen present in the gas. Å. process of gradual oxidation from on6 compound to a>noth.6r takes place, the final salts obtained depending upon the extent to which. the oxidation bas occurred. Aiiinioiiium. polysulphidc and. thiosu.lph.ate are the first products of oxidation, these being formed from ammonium sulphide, althoiigh, in the case of the former, the action is more mechanical tli.an Chemical. Oxidation, then, proceeds progressively, so that in turn the thiosulphate, sulphite and, lastly, sulphate are formed, whilst in certain cases free sulphur may be deposited. The sulpliite is usually only present in faint traces, which. is probably accounted for by the fact that solutions of polysulphide and sulpliite react to form sulphide and thiosulphate : (NH4)2S2 + (NH4)2S03 = (NH4)2S + (NH4)2S2O3. At the same time ammonium thiosulphate may be formed by reaction between the sulphite and sulphide. 4 (NH4)2SO3 + 2 (NH4)2S= 3 (NH4)2S203 + 6NH3 + 3H2O. Lunge asserts that ammonium polysulphide cannot exist in ordinary ammoniacal liquors, since it reacts with sulphites and cyanides. At one time there was some doubt as to whether gas liquor contained any actual free ammonia (i.e. dissolved NH3), but investigators such, as Gerlach and Tieftrunck have shown. this to be the case. Owing to the fact that acetylene is of a slightly acid nature, ammonium acetate (CH3C00NH4) may in some cases be found in gas liquor. Wlien. liquor is distilled witli an alkali (lime) for the manufacture of sulphate of ammonia, the final traces of ammonia are seldom expelled, so that some slight loss, amounting, under best conditions, to about 0'1 per cent., is inevitable. This is in some measure due to the fact that certain of the ammoma-bearing compoimds (such as the amine bodies) require rather more energetic treat-ment to bring about complete decomposition. 1 See Chapter VI, page 217. 2 See Chapter VIII, page 273.