The operation is carried on as in the English process : the sal ammoniac is deposited in the upper parts of the pots at A, A, and in the flower-pots p^p \. and gradually closes up the openings, so that towards the end of the operation, when the temperature has to be somewhat raised to give the product the requisite texture and trans- lucency, an internal pressure is caused in the pots. To obtain cakes of sufiBcient weight, it is necessary to recharge the pots several times. The hole is therefore cleared out with a tool like a centrebit, and the whole operation is repeated as at first. After two or three charges the cakes will have reached the greatest attainable thick- ness : the pots are allowed to cool and are broken to get out the sublimed cake, which, if the original salt was free from iron and tarry matter, will be found to be perfectly white and of higher purity than that made in iron subliming pans. If it is desired to obtain a grey sublimate, which some consumers prefer to the white one, a little fat is thrown into the pot from time to time during the sublimation. In some works, glass vessels, which are cheaper than the earthenware pots, have been employeiJ. The sublimation of sal ammoniac, especially by the French process, is a costly operation, whence the price of the sublimed salt is considerably higher than that of the crystallised salt. An attempt was made some years ago by the Lesage Company to replace the sublimed salt by a cheaper product, in the form of cakes 1 in. thick and 4 in. in diameter, obtained by strongly compressing the crystallised salt; but it did not meet with acceptance, and the manufacture was not continued. § 3. Ammonium Phosphates. . Phosphoric acid HgPO^, forms three compounds with ammonia, the normal or neutral phosphate (NH4)8P04, the diammonic, or intermediate phosphate (NHJgHPO^, and the monammonic, or acid MANUFACTURE OF LIQUID AMMONIA, ETC. 99 phosphate (NH4)H2P04. The first of these salts is not manufac- tured commercially; the two others, especially the intermediate phosphate, are now commercial products. The acid ammonium phosphate is prepared by treating acid calcium phosphate with ammonia and evaporating and crystallising the filtered solution ; the intermediate phosphate, by adding ammonia to a concentrated solution of the preceding. We take the following details of the manufacturing processes from the account published by Lagrange: — Acid calcium phosphate is prepared by treating finely powdered apatite or phosphorite with an equal weight of concentrated sulphuric acid in a cast-iron mixer with a mechanical stirrer. The mixture heats considerably and gives off gases rich in hydro- fluoric acid, which are carried off by a chimney. After six hours, the pasty mass, consisting of calcium sulphate, acid calcium phosphajbe, phosphoric acid, and the excess of sulphuric acid, is submitted to systematic extraction with water. For this purpose it is divided between four vats of equal capacity, each of which is furnished with a steam pipe. The contents of the first vat are • thinned with water, or the weak washings from a previous opera- tion, and are boiled up by steam. The solution is separated from the insoluble matter by filtration -through wicker baskets lined with filter cloth, and is passed in succession through the three other vats, boiling up in each of them. The residue on the filters is washed with boiling water and pressed. It consists almost entirely of calcium sulphate. The solution from the fourth vat, which marks 25° Be., and contains free phosphoric acid, acid calcium phosphate, calcium sulphate, and a little sulphuric acid, is treated with a small excess of barium carbonate, which removes the sulphuric acid completely. The clarified solution, now containing nothing but acid calcium phosphate, free phosphoric acid, and a little acid barium phosphate, is mixed with a small excess of ammonia, when all the calcium is precipitated as tribasic phosphate, which after washing is returned to the apatite mixer. The filtei^ed liquid is a 100 AMMONIA AND ITS COMPOUNDS solution of monammonic phosphate, which has now to be converted into the diammonic salt. If the operation has been carried out as described, this liquor will have a density of 20** Be., and this strength is necessary for the precipitation of the diammonic salt, which is effected by running the solution into small crystallisers, simultaneously with liquid ammonia of 22° (specific gravity, 0918), employing 1^ equivalents of ammonia for 1 equivalent of ammonic phosphate. The diammonic phosphate crystallises out as the solu- tions mix. The crystallisers must be covered to avoid loss of ammonia from the elevation of temperature which ensues. After cooling, the crystals are drained and pressed, whilst the mother liquor is distilled to recover the ammonia, which is used over again. The pressed crystals consist of pure diammonic phosphate, which is employed in Lagrange's sugar-refining process. § 4. Ammonium Carbonates. Three ammonium carbonates are believed to exist, the normal and acid salts, and the sesquicarbonate formed by the combination of the two former, but of these the normal salt has never been isolated, in consequence of the readiness with which it parts with its ammonia. It is therefore only known in solution, and the prismatic crystals which separate from an alcoholic solution of the sesquicarbonate, saturated with ammonia, are the simple sesqui- carbonate. The bicarbonate or acid carbonate is obtained by saturating an aqueous solution of the sesquicarbonate with carbonic acid. When commercial ammonium sesquicarbonate is treated with small quantities of water or alcohol, neutral carbonate is dissolved out, and a residue of bicarbonate, which is insoluble in alcohol, is left. On exposure to air the sesquicarbonate loses ammonia and is converted into the acid carbonate ; the latter slowly volatilises, giving off an ammoniacal odour. It crystallises from water in large orthorhombic prisms. Ammonium bicarbonate has been met with in crystalline masses, of yellowish white colour and density 145, in the guano deposits of Peru, Chili, and the western coast of Patagonia. Ammonium Sesquicarbonate : preparation from Animal Matter. — Pure ammonium sesquicarbonate is obtained by dissolving the commercial carbonate in caustic ammonia and allowing the solution MANUFACTURE OF LIQUID AMMONIA, ETC. 101 to crystallise : it separates in large orthorhombic prisms, which on exposure to air become opaque, and are converted into the bi- carbonate. The commercial article {ml volatile) consists chiefly of the sesquicarbonate. When animal matters, such as bone, horn, leather clippings, or muscular tissue, are submitted to dry distillation, the organic matter is decomposed and yields ammonium carbonate mixed with a little sulphide, water, and complex oily products. The quantity of ammonium carbonate thus obtained varies with the nature of the raw material, with the mode of distillation, the temperature employed, and the perfection of the condensation. Ammonium carbonate, which is the principal product, is partly deposited in the solid form in the coolers, if dry materials have been employed and water has not been added to assist the condensation. The product thus obtained, in crusts, stained yellow by the presence of tarry matter, was formerly known as scdt of hartshorn, whilst the aqueous solution obtained at the same time was called spirit of hartshorn. The purification of these products is long and difiBcult. Sublimation is the only method applicable ; it yields a product containing traces of empyreumatic substances, which is known in pharmacy as amnioniacum carhonicum pyro-oleum. This product may be com- pletely freed from its impurities by mixing it with animal charcoal and resubliming. It is then white, translucent, and fibrous, has an ammoniacal odour and caustic taste. These operations being costly, it is preferable to convert the impure carbonate, obtained as we have described in Chap. III., into sulphate, and from this obtain the pure carbonate at once. Either ammonium chloride or sulphate, mixed with twice its weight of chalk, may be used. The mixture is heated in a cast-iron retort, connected with a leaden receiver cooled by water. The mixture is gradually heated to dull redness ; ammonia, water vapour, and ammonium sesquicarbonate are evolved, and the last condenses as a white mass in the receiver. The addition of a little wood charcoal ,to the retort charge improves the colour of the product. English Process. — In England, ammonium carbonate is manu- factured from the crude chloride obtained by neutralising gas liquor with hydrochloric acid. The crystallised salt thus obtained is dis- tilled with twice its weight of chalk in horizontal cast-iron retorts 102 AMMONIA AND ITS COMPOUNDS 2 iiL long and 05 m. wide, similar to those in use for making coal gas. These retorts, of which three to five are set in the same famace, are connected by large cast-iron pipes with two small leaden chambers, 2 m. high, 2
long, and 075 m. wide, arranged in series, and employed as condensers for the ammoniimi carbonate. Each of these chambers has one of its sides movable, for the removal of the product, and there is a small pipe which allows the escape of a little water vapour and a solution of ammonium carbonate, which is collected and returned to the process. The materials employed must be thoroughly dry, and during the whole of the distillation the mixture must be stirred by a rod passing through an opening in the door of the retort. As ammonium carbonate begins to sublime at about 50° C, the firing must be done with care and regularity. As soon as a charge is exhausted it is drawn from the retort and a fresh one introduced, and the sublimation proceeds for fourteen or fifteen days before the receivers are opened to remove the product. The condensed car- bonate forms crusts, somewhat coloured by tarry matter, and rendered impure by small quantities of lime salts carried over by the current of gas. It is purified by a resublimation, conducted very slowly in cast-iron pots, 033 m. in diameter and 0'75 m. high, covered with leaden domes, and heated by the flue gases of the retort furnaces. These pots are sometimes replaced by large pans, 4 or 5 m. long, 075 m. wide, and 075 m. deep, covered with cast-iron plates luted on air-tight, and pierced with eight circular holes 0'33 m. in diameter, on which the leaden domes are adjusted. The crude salt from the chambers is placed in the tank with a certain quantity of water, and the leaden domes having been put in their places, the boiler is gently heated, the heat being controlled by observing a thermometer inserted into the dome the most distant from the fire. The operation lasts fourteen days, and the ammonium carbonate is then found in the domes in the form of white, translucent, fibrous crusts, which only require the removal of the surface which has been in contact with the metal. The liquid remaining in the pan receives a new charge of the crude salt, and a fresh sublimation is commenced. Uses. — Pure ammonium carbonate is used in medicine, and as a baking powder in making pastry to give lightness to the paste. It may be used for the preparation of any other salt of MANUFACTURE OF LIQUID AMMONIA, ETC. 103 ammonium, and in common with caustic ammonia it may be employed for the removal of grease from fabrics, and for develop- ing the dyes obtained from lichens. Its chief use is, however, for the decomposition of sodium chloride in the manufacture of sodium carbonate.
Key Takeaways
- Ammonium carbonate can be extracted from animal materials like bones and horn through dry distillation.
- The process involves sublimation, which requires careful temperature control to avoid impurities.
- Purification of the resulting ammonium carbonate is crucial for its intended uses.
Practical Tips
- Dry distill animal materials thoroughly before processing to ensure a higher yield of ammonium carbonate.
- Use leaden domes and carefully controlled heat in sublimation pots to prevent impurities from affecting the quality of the final product.
- Regularly monitor and adjust the temperature during the distillation process to maintain optimal conditions.
Warnings & Risks
- The process involves handling potentially hazardous chemicals and materials, so proper safety equipment is essential.
- Impure ammonium carbonate can be harmful if used in medical applications or food preparation.
- Sublimation requires precise temperature control; improper heating can lead to incomplete reactions or contamination.
Modern Application
While the techniques described in this chapter are archaic, the principles of extracting useful compounds from natural resources remain relevant. Modern survivalists can apply these methods by adapting them for use with available materials and equipment. For instance, understanding how to purify chemicals through sublimation or distillation can be crucial when dealing with limited resources during a crisis.
Frequently Asked Questions
Q: How is ammonium carbonate extracted from animal matter?
Ammonium carbonate is extracted by submitting animal materials like bones and horn to dry distillation, which decomposes the organic matter and yields ammonium carbonate mixed with other substances. The product is then purified through sublimation.
Q: What are the key steps in purifying ammonium carbonate?
Purification involves subliming the crude ammonium carbonate to remove impurities, followed by resublimation if necessary. This process requires careful temperature control and use of leaden domes or similar equipment.
Q: Why is it important to monitor the temperature during distillation?
Monitoring the temperature ensures that the sublimation process occurs at the correct rate, preventing incomplete reactions or contamination with impurities. Proper temperature control is crucial for obtaining high-quality ammonium carbonate.