MANUFACTURE OF AMMONIACAL PRODUCTS FROM BONES, (Part 3)

the impurities of the water employed for absorbing the gas, and traces of ammonium carbonate. To obtain a perfectly pure product, it should be redistilled with a little slaked lime, and the gas condensed in distilled water. Pure liquid ammonia leaves no residue when evaporated on platinum foil, gives no precipitate with calcium salts, and, after acidifying with pure nitric acid, does not precipitate silver nitrate. In our opinion the three caustic soda vessels of the apparatus here described might advantageously be replaced by a small cast- iron distillation column, through which the caustic soda lye would be allowed to flow. Liquid ammonia is lower in density than water ; it is sent out of several strengths according to the use for which it is intended. Most of it is sold at 22° Cartier ( = specific gravity 0918), a certain amount at 24° Cartier (0904), and a small quantity at 28° (0-881). Ammonia is employed in medicine as a rubefacient and re- vulsive, and to produce vesication. In small weak doses it is used as a corrective for alcoholic intoxication, and it is also employed in veterinary medicine as a corrective for flatulence. In the arts it is used for cleansing woollen fabrics, for mixing MANUFACTURE OF LIQUID AMMONIA, ETC, 91 with the scales of whiting for the manufacture of imitation pearls, for preparing ammoniacal cochineal liquor and archil. The liquid of density 0881 is used in the Carr6 and Lind^ freezing machines The greatest consumption, however, is in the manufacture of soda by the Solvay process, in which a solution of sodium chloride saturated with caustic iammonia is treated with carbonic acid gas. Density at 14° of Aqueous Solution of Ammonia (Carius). Ammonia per cent." Density. 1 Ammonia per cent. Density. Ammonia per cent. Density. 1 0-9959 13 0-9484 25 0-9106 2 0-9915 14 0-9449 26 0-9078 3 0-9873 15 0-9444 27 0-9052 4 0-9831 16 1 0-9380 28 0-9026 5 0-9790 ' 17 ; 0-9347 29 0-9001 6 0-9749 18 0-9314 1 30 0-8976 7 0-9709 19 0-9283 31 0-8953 8 0-9670 20 0-9251 1 32 0-8929 9 0-9631 21 0-9221 1 33 0-8907 10 0-9593 22 0-9191 i 34 0-8885 11 0-9556 ' 23 0-9162 35 0-8864 12 0-9520 24 0-9133 36 0-8844 § 2. Ammonium Chloride (Sal Ammoniac). 1. Manufacture from fermented urine, — A small amount of this salt is obtained by neutralising with hydrochloric acid the solution of ammonium carbonate obtained by Margueritte and SourdevaFs process for the treatment of eau vanne. This solution is worked up by the Lesage Company partly for the manufacture of ammonium chloride. The solution of ammonium carbonate is drawn out into carboys, which are then placed on a platform by the side of a large rectangular lead-lined vat, with a cover and draught pipe leading to a chimney. The solution is run down into the vat by syphons of glass or lead, whilst simultaneously, from another set of carboys, ordinary commercial hydrochloric acid of 18° to -20° B^. is run down in such quantity as to keep the mixture neutral. Through- out the operation a mixture of carbonic acid and hydrogen sulphide gases is evolved, which is carried off by the chimney, whilst the temperature of the liquid rises, and unless care is taken ammonium carbonate would be lost by volatilisation. The mixture is left slightly acid at the end of the operation, and the solution is then 92 AMMONIA AND ITS COMPOUNDS evaporated by passing steam through a coil of lead pipe lying at the bottom of the vat. During the evaporation the cover of the vat is removed, but temporary wooden flaps are laid on it in such posi- tions that the steam is carried off by the chimney instead of escaping into the workshop. When sufficiently concentrated, the solution is run down into lead-lined crystallisers, where it cools slowly and deposits a perfectly white salt. In this operation, metal taps, which would be rapidly corroded by the solution, are replaced by rubber tubes closed by compression clips. To obtain the salt in small crystals, great attention must be paid to the degree of concentration of the solution, and the contents of the crystallisers must be stirred several times a day. When the crystallisation is completed, the mother liquor is returned to the neutralisation vat for a subsequent operation, and the salt is removed by wooden shovels, drained in baskets, and dried. Kuentz has suggested the following method of utilising directly the ammonia gas from the distillation columns in which fermented urine is treated ; native calcium phosphate is decomposed by hydro- chloric acid so as to obtain acid calcium phosphate and calcium chloride, Gq.^{VO^\ + 4HC1 = (^q.'R^{VO^\ + 2CaCl2. This mixture is then treated in a closed vessel with the ammoniacal vapours from the still, which consist mainly of ammonium carbonate with a little ammonia, or it may be treated with the concentrated ammoniacal liquor. A precipitate is produced consisting of dicalcic phosphate and calcium carbonate, which is valuable as a fertiliser, whilst the whole of the chlorine is obtained as a solution of ammonium chloride, which is separated and crystallised. The uncondensable gases are passed through lime and then burnt in a coke fire. As far as we are aware, this ingenious process has not been practically employed on the large scale. 2. Manufacture from Gas Liquor, — In England and Scotland much sal ammoniac is manufactured from tarry gas liquor, the liquor, freed as far as possible from tar by subsidence, being directly neutralised by hydrochloric acid and evaporated. The liquors are placed in large wooden vats furnished with mechanical stirrers, and ordinary commercial muriatic acid is gradually run in ; the gaseous products, which in this case carry off some tarry matters, are passed through a fire in the usual manner. Much of the tar, which was held in solution by the ammonia, becomes insoluble when the alkali MANUFACTURE OF LIQUID AMMONIA, ETC. 93 is neutralised, and is separated from the liquid by prolonged sub- sidence. The clarified liquor, which is strongly coloured, is boiled down in cast-iron pans set directly over a fire. A further quantity of tar becomes insoluble as the concentration progresses, and is removed by skimmers. A small quantity of chalk or lime is added to the pans to neutralise free acid and prevent the boilers from being attacked. When concentrated to specific gravity 125, the solution is run down into crystallisers, in which it is stirred three or four times a day during the crystallisation to promote the formation of small crystals, which are more suitable than large ones for sub- liming. The crude ammonium chloride is obtained in granular crystals of a deep brown colour, due to the presence of tarry matter. It is partially purified by heating it on cast-iron plates, the volatile tarry substances and the water being driven off, whilst the remaining tarry matter becomes carbonised ; at the same time the ammonium sulphate and thiosulphate, which the crude salt always contains, are decomposed. By careful working, and constantly stirring the mass, this operation can be conducted without appreciable loss of ammonium chloride. The greyish product is then sublimed, and yields commercial sal ammoniac^ as a white mass, of fibrous structure and of a high degree of purity (see below. Chap. v. 6). Kuentz has proposed to manufacture ammonium chloride in gas- works by treating the crude gas liquor directly with impure ferric chloride obtained from pyritic schist and common salt. A weak solution of ammonium chloride is thus obtained, together with a precipitate of ferric hydroxide mixed with a little sulphur, which may be used in the gas purifiers. The gas liquor is treated with the ferric chloride solution as long as any precipitate is produced, and the mixtiu-e is thrown upon a filter. .The clear filtrate is evaporated by waste heat, and the precipitate, mixed with sawdust to render it porous, and gently dried, forms a very efficient purifying material. In this way, by the use of a very inexpensive material, the ammonia in the gas liquor can be completely converted into ammoniiun chloride without the evolution of any offensive gases. A process for the purification of coal gas has also been adopted in France by Mallet, by means of the residual liquor from the pre- paration of chlorine, which yields a precipitate of manganese carbonate and sulphide, with ferrous sulphide, and a solution of ammonium chloride. Many of the processes employed for working 94 AMMONIA AND ITS COMPOUNDS up gas liquor or fermented urine yield a product containing 14 to 18 per cent, of ammonia in the form of carbonate. Anj of these liquors can be used for making ammonium chloride by the same process as that adopted in the case of the product from Margueritte's ap]>aratus. Kuentz has also suggested, as a means of avoiding the evolution of gas during the neutralisation of these solutions, to treat them in the cold with a solution of calcium chloride, and pass the mixture through a filter press. The filtrate, feebly acidified by hydro- chloric acid, is then evaporated. This process would seem to be an economical one, if the almost valueless calcium chloride from the ammonia-soda process is employed. The solutions of ammonium chloride are always evaporated in metal pans, either by direct fire, as in England, or by steam. If iron jians are employed, the metal is acted on, and a double chloride of iron and ammonium is produced, which volatilises when the salt is sublimed, and gives a coloured product. This inconvenience may be obviated by the addition of acid calcium phosphate, which forms non-volatile ferric j^hosphate, or by evaporating the solutions in leaden vessels. The ammonium chloride employed for charging the Leclanche batteries used in telegraphy, must be free from lead. To prepare it for this jjurpose, it must be freed from heavy metals by treating the solution with ammonium sulphide, and filtering before it is left to crystallise. 3. Ammonium Chloride from the distillation of Animal Matter, — Laming has proposed to purify the distillate obtained in the manu- facture of bone charcoal by means of fatty oils, and to treat the purified liquors with calcium chloride. A process has also been worked out by J. B. Divis, which yields a product pure enough to be used without subliming. The distillate is left at rest in wooden vessels for three or four days, and the tar which collects at the surface is skimmed off. The liquor is then gently heated and mixed with a strong solution of calcium chloride, in such quantity that the solution just ceases to effervesce with hydrochloride acid, excess being carefully avoided. The precipitate of calcium carbonate carries down the impurities, and after pressing can be used as a manure, whilst a solution of ammonium chloride of fair purity is obtained. The solution, which is slightly yellowish, is boiled up^ MANUFACTURE OF LIQUID AMMONIA, ETC. 95 skimmed, and filtered hot through a mixture of coke and wood charcoal, supported by a layer of straw, in a wooden vat 125 to 15 m. high, and 045 to 06 m. in diameter. The filtered liquor is evaporated in a shallow pan, furnished with a cover and draught- pipe leading to a chimney to remove the offensive vapour. Fresh solution to run in as the evaporation proceeds, and when the surface becomes covered with a saline crust the evaporation is stopped^and the ammonium chloride which has salted out is re- moved to conical moulds resembling those used in sugar refining. The contents of these moulds are stirred to promote the formation of small crystals, and when crystallisation is complete the points of the moulds are pierced, the mother liquor allowed to drain away, and the crystals washed by percolation with a saturated solution of the salt, obtained by removing the upper portion of the crystalline mass to a depth of about an inch, and dissolving it in water. Two more washings are given with solutions of white salt ; the contents of the moulds are then turned out, crushed with a wooden pestle, and allowed to dry. The mother liquor and the first washings are boiled down; later percolates are used for the first washings of fresh charges. The ammonium chloride obtained is of a high degree of purity, being free from calcium and iron, and having only a faint tarry odour. 4. Manufacture from Ammonium Sulphate, — From the year 1795 sal ammoniac and sodium sulphate were manufactured by Payen at Grenoble by decomposing common salt with a hot solution of ammonium sulphate of 21° Be. ; the sodium sulphate crystallises out, leaving ammonium chloride in solution. For the manufacture of sodium sulphate this process has long been displaced by more economical methods. The reaction has, however, been utilised in England more recently for the manufacture of ammonium chloride from gas liquor. The ammonia in the gas liquor is concentrated by distillation and neutralised by chamber sulphuric acid, and to the solution so obtained sodium chloride is added. On boiling down the mixture the less soluble sodium sulphate salts out, and is fished from the evaporating pans, drained, and washed, to free it from adhering ammonium chloride. When saline crusts begin to form on the surface of the liquid, the concentration is stopped ; the liquid is left at rest to deposit the sodium sulphate, and the solution is run into lead-lined crystallisers. After cooling, the 96 AMMONIA AND ITS COMPOUNDS mother liquor is run off, and the crystallised salt is dried and sublimed or purified by recrystallisation. The following table shows the solubility of ammonium chloride in water at various temperatures : — Aoiinonium Chloride \ Anmionium Chloride Temperature dissolved by 100 parts of ' Temperature. dissolved by 100 parts of Water. Water. 5" 28-40 60" 55-64 10" 32 84 70" 59-48 20" 37-28 80" 63-92 30" 41-72 90" 68-36 , 40" 46-16 100" 72-80 1 50" 50-60 110° 77-24 5. S^tblimation, — Ammonium chloride obtained by any of the above processes may be purified by sublimation. Originally obtained from Egypt and certain Asiatic localities, sal ammoniac was brought to Europe as early as the seventh century, in cakes with a fibrous fracture, more or less stained with empyreumatic substances. At the present day two modes of sublimation are in use. The French method yields small white or grey cakes, which resemble in appearance those brought formerly from Egypt, and for which there is a constant demand, whilst the English method produces larger and thicker crusts. The dried salt, when heated, volatilises, and the vapour con- denses on the cooler parts of the vessel, forming a white translucent layer. In this operation it is essential that the temperature should be constantly maintained at the point at which the sublimation proceeds slowly : at too high a temperature a considerable loss would be incurred, the cake would not possess the correct texture, and would be contaminated by empyreumatic products, resulting from tarry matters which were not destroyed by the roasting. In England the sublimation of ammonium chloride obtained from gas liquor is carried out in large cast-iron subliming pans lined with fire-brick, and furnished with cast-iron covers, which are fixed down by keys, so as to make a tight joint capable of resisting the internal pressure developed during the sublimation. It is on the under side of these covers that the sal ammoniac is deposited, in a layer 4 to 6 in. thick. The pans used are from 3 to 9 ft. in diameter, and take charges of 1 to 9 tons each. The covers can be raised by a chain pulley afl&xed to the roof. MANUFACTURE OF LIQUID AMMONIA, ETC. 97 When a pan has been chained and covered, it is at firet heated rapidly to the temperature of sublimation, after which the heat is regulated so that the operation proceeds slowly and uniformly. A small hole in the cover allows the escape of the air, with small quantitieB of gas and steam ; it is closed by an iron plug as soon as fumes of sal ammoniac appear. To prevent the covers from cooling too rapidly, a layer of sand or ashes is placed upon them. The operation is not continued long enough to sublime the entire chaige, as impurities accumulate in the last portion, and would, if volatilised, injure the colour of the product. "When a sufficient quantity of this impure residue has accumulated from successive chains, it is removed and washed, and the solutions are Fia. 2S. — Furnace for the subliinatioa of sal ammoDiac ia pots. added to those in the evaporating pans. A sublimation lasts about a week : when the pan has cooled sufficiently, the cover is raised, the crust is detached, and any portions coloured by contact with the iron are removed, and returned to subsequent operations. In France the sublimation is always performed in earthenware pote 0'5 m. h^h and 03 to 035 m. in diameter. Fig. 28 shows the arrangement adopted. The pots, twenty in number, are arranged in two rows on the arch of a furnace, where they are exposed to the flames rising through the apertures 0, 0. The top of the furnace is formed by a cast-iron plate F, F, through holes in which the pots are introduced, and which confines the heat to the lower two-thirds of their height. On this plate lies a layer of sand, which 98 AMMONIA AND ITS COMPOUNDS can be heaped over the pots when required. The pots, first coated with a clay lute, are dried in the subliming house ; they are then charged with crystallised ammonium chloride as dry as possible, set in the furnace and covered with sand. The heat is then raised slowly, to avoid cracking the pots. Steam is at first given oflf from the openings S, S, and when thick white vapours of sal ammoniac appear, an ordinary flower-pot p is inverted over each openiDg to condense them.