CHEMISTRY).
Salts.—Ammonium fluoride, NH,F, may be obtained by neutral izing ammonia with hydrofluoric acid ; it has a sharp saline taste, and the crystals are very soluble in water; it decomposes silicates on being heated with them. It is a powerful preservative.
Ammonium chloride, NH,C1. (See SAL-AMMONIAC.) Ammonium bromide, NH,Br, can be prepared by the direct action of bromine on ammonia. It crystallizes in colourless prisms which have a saline taste and are very soluble in water. Like the chloride, it sublimes on heating. It is sometimes used medicinally instead of potassium bromide.
Ammonium iodide, NH,I, can be prepared by the action of hydriodic acid on ammonia. It is soluble in alcohol and exceed ingly so in water. It turns yellow on keeping, unless kept in sealed tubes away from light. With iodine it gives the tri-iodide, if chlorine is passed into its solution in which iodine is suspended, the comparatively stable dichloroiodide, is obtained.
Ammonium chlorate, decomposes at about Ioo° C. into nitrogen, oxygen and chlorine. The perchlorate, NH,C10,, obtained from an alkaline perchlorate and an ammonium salt, has been used in high-explosive shell, but is rather too sensitive to shock.
Ammonium carbonates. The commercial salt is known as sal volatile or salt of hartshorn; it is obtained by heating the chloride or sulphate with chalk and condensing the vapours. When resub limed, it forms hard fibrous masses of composition (i.e., bicarbonate and carbamate in molecular proportion), or, more probably, which is a sesquicarbonate ; it!" possesses a strongly ammoniacal smell. The normal carbonate, is obtained by saturat ing a concentrated solution of the foregoing with ammonia ; it can be obtained in a crystalline condition, but readily loses ammonia on exposure and reverts to the sesquicarbonate.
The bicarbonate, is obtained by saturating a solution of the commercial carbonate with carbon dioxide; it is sparingly soluble in water and readily loses carbon dioxide.
Ammonium thiocyanate (or sulphocyanide), NH,NCS, can be obtained from carbon disulphide and ammonia; it isomerises to thiourea, which is used in the rubber industry; it is also of use in quantitative analysis (see CHEMISTRY: ANALYSIS).
Ammonium nitrate, prepared from the acid and am monia, exists in four different crystalline forms which are, respec tively, stable over the temperature ranges: below — 16°, — 16° to 32°, 32° to 84°, and 84° to 169.6° (the melting point). Its dis solution in water produces a considerable lowering of temperature which is utilized in freezing mixtures. On being gently heated it is decomposed into water and nitrous oxide: Ammonium nitrite, is formed in the oxidation of am monia by ozone or hydrogen peroxide ; it is best obtained by double decomposition of sodium nitrite and ammonium chloride, the resulting sodium chloride being much less soluble; if silver nitrite is used the product is purer. The solution can be concen trated to give crystals which can be sublimed in a vacuum at 8o° C, but they readily decompose to give water and nitrogen: Ammonium phosphates. The normal phosphate, can be obtained by adding excess of ammonia to the acid phos phate, or to a concentrated solution of the acid; its solution readily loses ammonia. The diammonium hydrogen phos phate, is obtained by evaporating the 'foregoing solutions; on heating, the crystals melt and decompose, leaving a residue of metaphosphoric acid, The dihydrogen phos phate, (NH,)H2P0,, crystallises from solutions which are dis tinctly acidic with phosphoric acid.
Ammonium sodium hydrogen phosphate, (NH,)NaHPO,, is known as microcosmic salt (q.v.).
Ammonium sulphate, (NH,)2S0,, is prepared from the am moniacal liquor of gas-works (see GAS : MANUFACTURE) and puri fied by recrystallization. The aqueous solution tends to lose am monia on boiling. Its chief use is as an artificial manure, and much of that being sold for this purpose is made from synthetic ammonia.
Ammonium persulphate, is prepared by the electro lytic oxidation of a cold, saturated solution of the sulphate, in the presence of dilute sulphuric acid, a high anodic current density being used; it is more conveniently obtained by double decom position from ammonium chloride and sodium persulphate. It is difficult to prepare in a state of high purity, and is very soluble in cold water (58 grams in I oo grams of water at o° C.) .
Ammonium sulphide, is obtained as micaceous crys tals by passing sulphuretted hydrogen and a slight excess of am monia through a well-cooled vessel. Excess of the sulphuretted hydrogen gives rise to the hydrosulphide, NH,HS. Both are very soluble white solids. The former is usually sold as a concentrated aqueous solution, which finds a considerable use in analysis. The sulphide solution dissolves sulphur to give a series of ill-defined polysulphides.
According to A. E. H. Tutton, many of the ammonium salts display a close resemblance to the corresponding salts of rubidium and caesium in their crystallographic characteristics, the similarity being especially striking in the case of the former metal.
Ammonia readily combines with many metallic salts (as with calcium and silver chlorides, above) to give ammines (q.v.), which are often of great theoretical interest. See also MERCURY for the "infusible" and "fusible white precipitates" of pharmacy.
Compounds are known which may be regarded as derived from ammonia by the replacement of hydrogen atoms by the sulpho group ; thus, potassium ammon-trisulphonate, is obtained as a crystalline precipitate by the addition of excess of potassium sulphite (or metabisulphite) to a solution of potas sium nitrite: It can be recrystallized from alkaline solution, and on boiling with water is converted successively into the disulphonate, and monosulphonate, the latter being the salt of the stable aminosulphonic acid. The chief interest of the disulphonate lies in the fact that its hydrogen atom is acidic, for the corresponding ammonium salt, gives a triammonium salt NH,•N and both of these are formed by direct union of sul phur trioxide and ammonia. For further details of such com pounds, the works of E. Divers and of F. Raschig should be con sulted, especially the latter's Schwe f el- and Sticksto ff studien, 1924.
Hydrazine. If a solution of sodium hypochlorite is added to a fairly concentrated solution of ammonia containing o• 2 % of glue, hydrazine, or chloroamine, NH,C1, is produced accord ing to the conditions; the latter is fairly stable and may be dis tilled in a vacuum.
Detection and Estimation.—Solutions of ammonia and am monium salts, even if very dilute, give a distinct yellow or yellow ish-brown coloration with Nessler's solution, owing to the forma tion of a complex iodide, which is obtained as a pre cipitate from stronger solutions ; this is also the basis of a colorimetric method for estimating minute traces of ammonia in drinking-water. Larger quantities of ammonia or its salts can be detected by the evolution of the characteristic smell of the free ammonia on heating with caustic alkalis or lime. The quantita tive estimation may be effected by (I) distillation of salts or ammoniacal liquors with sodium or potassium hydroxide and absorption of the liberated ammonia in an excess of standard sul phuric acid, the excess being titrated by alkali; (2) by absorption of ammonia in hydrochloric acid and precipitation as the chloro platinate, or (3) by the addition of neutral formal dehyde to a neutral solution of an ammonium salt, whereby hexamethylenetetramine is formed and the acid originally in combination with the ammonia is set free and may be titrated: (A. D. M.) (See REFRIGERATION AND ICE MANUFACTURE.)