Ammonium, Chloride of

NH 4 Cl. Syn. Muriate of ammonia , Sal ammoniac , Hydro chlorate of ammonia ; Chlorohydrate d’ammonia que , Sel ammoniac , ., Fr.; Salmiak , Ger. A substance which, as already noticed, appears to have been originally obtained, by sublimation, from the soot of camels’ dung, in Egypt. In this country, at the present day, it is manufactured chiefly from the crude ammoniacal liquors obtained as secondary products in the manufacture of coal-gas and animal charcoal. Prep. 1. From GAS-LIQUOR :—The crude ammoniacal liquor of the gas-works is, either at once, or after distillation, [48] neutralised with hydrochloric or sulphuric acid, the choice being given to the one which is the cheaper and more acce ible at the place where the works are situated. When hydrochloric acid is employed, the SATURATION is usually effected by allowing the acid to flow from a large wooden ve el or tank lined with lead or gutta perch a into a large underground reservoir or tank containing the ammoniacal liquor, and having an exit-tube pa ing into the chimney or shaft of the steam-engine, to carry off the sulphuretted hydrogen and other offensive gases liberated during the mixture. Sometimes the gas-liquor is accumulated in enormous covered wooden tuns, capable of holding from 10,000 to 20,000 gallons, or more; and the acid is added by raising the gutta-perch a carboys containing it by means of cranes, and then thoroughly mixing it with the liquor by means of powerful ‘agitators,’ whilst the offensive fumes are either pa ed off as before, or made to traverse the fire of the steam-engine before entering the chimney-shaft. The quantity of acid employed to effect saturation must, of course, depend on the ammoniacal strength of the gas-liquor operated on. The usual proportions are 1 1 ⁄ 2 to 2 lbs. of the former, to each gal. of the latter; but in all cases sufficient should be added to impart a very faint acid reaction to the mixture. This last having been effected, the saline solution, now containing hydro chlorate of ammonia, is, after repose, ready to be pumped or run off into the evaporators. [48] This is now generally conducted in a large wrought-iron boiler, connected with a rude modification of Coffey’s still; the object being to obtain the liquor freer from tar and more concentrated. The EVAPORATION of the crude saline solution is usually carried on in large square or rectangular cast-iron vats, of very moderate depth, and capable of holding from 1000 to 1500 gallons, or more. These are encased in brickwork, and are heated by a furnace, of which the flues pa in a sinuous course beneath the lining of brickwork on which the vats or pans rest. During the concentration of the liquid, the tar, ., which separates and floats on the surface, and which thus seriously impedes evaporation, is, from time to time, removed by skimming. As soon as the sp. gr. reaches 1·25, any exce of acid in the solution is exactly neutralised with a little fresh ammoniacal liquor; by which any waste of acid is prevented, at the same time that any ferric salt present, and which would contaminate the ultimate product, is precipitated as sesquioxide. After settling for a short time, the hot liquor is ready to be transferred to the crystallisers. The ve els employed in the CRYSTALLISATION are pans or tubs, usually circular and about 7 or 8 feet wide, by 2 1 ⁄ 2 to 3 feet deep; and are generally set on the ground, or are embedded either partially or wholly in it. The saline liquor being pumped or run into them at a little below the boiling temperature, crystallises as it cools; the only interference being occasional stirring or agitation, to prevent the formation of large crystals, which would be inconvenient in the subsequent part of the proce . The time occupied in the crystallisation varies, according to the size of the ‘crystallisers,’ and the weather, from 3 or 4 to 8 or even 10 days. The ‘mother-liquor’ of the ‘crystallisers’ is pumped back into the evaporating pans for further concentration. The crude blackish salt (hydro chlorate) thus obtained is contaminated with tarry and oleaginous matter, free acid, water, .; from part of which it is freed by exposing it in a layer about 4 inches deep, on a cast-iron plate gently heated by a zigzag flue of a small furnace, until all the water is expelled; care being taken that the heat never rises high enough to volatilise the salt. This operation is generally performed under a dome, or the expanded throat of a large chimney. The salt will now have become of a greyish-white colour, and is ready for the next operation. IMG:596405606043057898_i144.png: The crude dried salt of the last proce is finally purified by sublimation. For this purpose cast-iron-pots lined with clay, and heated from below and by flues round their sides, are employed. (See engr. ) The crude grey salt is beaten down into these pots until they are about 2-3rds filled, when the heads or capitols are fitted on, and heat applied. The latter are very heavy, being usually made of lead (sometimes of iron), and have the form of a dome, or a hemispherical cup, with a small tube or hole at the apex, in which a plug is loosely placed, to permit the escape of steam. These domes or heads are so made as to fit closely and firmly on the flat rim or flange of the ‘sublimers,’ and are retained in their places, during use, both by their weight, and by 2 or 3 clamps provided for the purpose. They are also furnished with 3 rings, set at equal distances, to allow of their being lifted off, or moved, by means of a pulley and chains. The due application and regulation of the heat is here of the utmost importance. If the temperature employed be too high, the sublimed salt will be contaminated with empyreumatic matter, while some of it will be carried beyond the dome and lost; and if it be extreme, the head may be altogether blown off, and the contents of the pan scattered about the building; whilst on the other hand, if the heat employed be too low, the resulting cake of sal ammonia will be soft, spongy, and either grey or yellowish. The proper temperature is said to be known by two or three drops of water readily boiling, and being di ipated in vapour, when placed on the head or cover of the sublimer; but it should not ‘spit’ or ‘dance about,’ or be raised by the heat out of contact with the metal. The usual practice is to keep the fires “briskly up until the sublimers and their surroundings attain a sufficient degree of heat; they are then slackened, and maintained at a mean temperature.” (Muspratt.) The sublimation occupies from 5 to 9 days; but it is customary to raise the heads once, or even twice a week, to ascertain the progre made; the fires having been purposely neglected or checked for some hours previously. The proce is finally stopped before the whole of the crude salt in the pots is volatilised; since the heat required for that purpose would lead to the decomposition of the carbonaceous impurities, and cause them to emit volatile hydrocarbons, which would materially le en the purity and beauty of the product. The unsublimed portion in the pots forms a conical ma , which is technically called the ‘yolk.’ This is shown in the second engr. (see below ), in which the latest improvements in the form of the subliming apparatus are also exhibited. IMG:596405606043057898_i145.png: The sublimation having been carried to a sufficient extent, the fires are allowed to die out. The domes, after cooling, are lifted off, and the attached hemispherical cakes or ‘bells’ of SAL AMMONIAC or HYDRO CHLORATE OF AMMONIA at once removed. These vary from 2 to 5 inches in thickne , and from 45 or 50 lbs. to 1000 lbs. , and upwards, in weight, according to the size of the sublimers in which they have been produced. They are generally nearly pure, except in the outer part which has been in contact with the metal. From the subliming-house they are taken to the store or packing-house, and after having been scraped, to remove the discoloured portion before alluded to, are either preserved entire, or are broken up into convenient pieces, which are then packed in casks or barrels, and in either state are ready for the market. When sulphuric acid [49] is used to neutralise the ammoniacal liquor, the proce is generally, for the most part, the same as when hydrochloric acid is employed; but here the brown salt obtained by the crystallisation, and subsequent desiccation, is crude SULPHATE OF AMMONIA , instead of the hydro chlorate. It is intimately mixed with about an equal weight of chloride of sodium (common salt) before being put into the sublimers. [49] Sp. gr. 1·33 to 1·38. In some cases, particularly where the ammoniacal liquor is rich in carbonate of ammonia, gypsum is employed as a source of sulphuric acid. (See below .) Another method is to convert the solution of the crude sulphate into a solution of the hydro chlorate, during the proce , by the addition of chloride of sodium. Both these last methods are described below. 2. From BONE-LIQUOR , . [50] —The ammoniacal liquor technically called ‘bone-liquor’ or ‘bone-spirit,’ and formerly known under the name of ‘spirit of hartshorn,’ is e entially a solution of carbonate of ammonia more or le contaminated with volatile empyreumatic oil. Its conversion into SAL AMMONIA may be easily effected by saturating it with hydrochloric acid, evaporating the resulting neutral solution in lead or iron boilers until a pellicle begins to form, then pumping or running off the hot liquors into the crystallisers, and, lastly, draining and drying the crystals. The salt thus obtained may be purified either by sublimation or by recrystallisation. The whole series of proce es closely resemble those already described, except in being le troublesome, owing to the absence of the tarry and other foreign matters which impede and complicate them when gas-liquor is employed. [50] That employed in England is chiefly obtained, as already mentioned, from the manufacturers of bone-black or animal charcoal; but, on the Continent, the liquor obtained by a like destructive distillation of various animal offals (blood, flesh, horn, hoofs, woollen rags and waste, hair, scrapings of hides, leather cuttings, .) is employed for the same purpose. The preparatory proce by which this liquor is obtained is e entially the same in each case; except that with animal offal the temperature should not exceed a red-brown heat, in order that the resulting charcoal may afterwards serve to make ferrocyanide of pota ium and Pru ian blue. These liquors have usually a density ranging between 8° and 9° Baumé (Ure; = sp. gr. 1·056 to 1·063). Another method adopted, particularly on the Continent, and one equally applicable to any crude ammoniacal liquor rich in free ammonia or its carbonates, is to employ sulphate of lime instead of sulphuric acid to neutralise the alkali. For this purpose the ammoniacal liquor is pa ed through a series of three or four covered wooden filters lined with lead, each containing a layer of crushed gypsum to the depth of 3 or 4 inches. These filters are usually set on ‘stages’ one above another, and each communicates with a cistern placed beneath it by means of a leaden pipe furnished with a stop-cock. This last is not opened untill the liquor has remained some little time in the filter; and a pump throws back once, or oftener, upon each filter, what has already pa ed through it, before it is allowed to run into the next lower one. The ‘liquor’ in each filter is not allowed to stand higher than from 2 to 3 inches above the surface of the gypsum; and the lowest or last filter is supplied with fresh gypsum at each separate charge of fresh liquor. A little water is lastly pa ed through the filters to wash out the portion of ammoniacal liquor absorbed or retained by the filtering media. In this way the gypsum of the filters is converted into carbonate of lime at the expense of the carbonate of ammonia in the solution; whilst the ammonia of the latter decomposes the gypsum, and becomes converted into sulphate of ammonia, which, with some free ammonia, is found in the filtrate. Sulphuric acid is next added to the filtered liquor to completely neutralise the free and carbonated alkali still existing in it; after which it is evaporated in a leaden boiler, with frequent skimming to remove floating oil, until of the sp. gr. 1·160. Chloride of sodium (common salt), in sufficient quantity to convert all the sulphate of ammonia in the liquid into hydro chlorate, by double decomposition, is now added, with constant stirring; after which the clear portion is either pumped or syphoned off into a somewhat deep reservoir or tank, where it is allowed to settle. The liquid after sufficient repose is pumped from the reservoir to the boilers, and evaporated, with frequent agitation, so long as the sulphate of soda now existing in it falls to the bottom in granular crystals. These crystals are, at intervals, scraped to the cooler portion of the pan or boiler, whence they are removed by copper rakes and shovels, into draining-hoppers, placed near the edges of the pan. The liquor in the boiler is now a strong solution of sal ammoniac, but still containing a little sulphate of soda, from which it has to be freed by crystallisation. With this object it is further concentrated, and then run or pumped into the crystallisers. In 30 or 40 hours, or longer, the mother-liquor is run or pumped off. The ma of newly-formed crystals is then drained, and slightly washed, first with a little weak solution of sal ammoniac, and next with a very little cold water; after which they are again well drained. The crude HYDRO CHLORATE OF AMMONIA , thus obtained, is converted into the pure salts, by desiccation and sublimation, as before. In France, where this method is very generally employed, the sublimation is commonly conducted in stoneware or earthenware balloons or bottles coated with loam, of about 18 to 20 inches in height in the body, and either surmounted with inverted ‘cups’ or ‘heads’ 10 or 12 inches high, or simply covered with a tile, when (in the latter case) the sublimate collects in the upper part or neck of the balloon, which is above the action of the fire. A number of these ve els are set on the dome of a furnace, which is perforated with holes or slits, to allow the heat to pa through; whilst their necks or heads are sheltered from the action of the fire by plates of iron or earthenware, having semi-circular indentations on their edges, so that when placed together they form a level surface, through which the necks of the sublimers protrude, and fit closely. The fire is nicely regulated, so as to cause the salts to condense in the upper and cooler part of the ve els, or in the heads, as the case may be; and great care is taken to occasionally clear the necks with a skewer, to prevent choking, and consequent bursting. In Scotland, where a similar proce is also commonly pursued, the sublimers, according to Dr Ure, are generally “cast-iron pots, lined with fire-proof tiles; the condensation being effected in globular heads of green gla , with which each of the iron pots are capped.” [51] [51] Ure’s ‘Dict. of Arts, M., & M.,’ 5th Edn., i, p. 143. Ratio. Gas-liquor contains carbonate of ammonium (chiefly), with chloride, sulphate, hydrosulphate, cyanide, sulphocyanide, ., of the same radical. On neutralisation with hydrochloric acid, or sulphuric acid, these are converted into chloride or sulphate of ammonium, according to the acid used. By sublimation with chloride of sodium, the sulphate of ammonium is converted, by double decomposition, into chloride of ammonium, which sublimes; and sulphate of sodium, which remains in the subliming pot. A similar change occurs when the solution of the sulphate, prior to crystallisation, is decomposed by the addition of chloride of sodium, or any other chloride. When the ‘gas-liquor’ is at once converted into chloride of ammonium by the addition of hydrochloric acid, the sublimation merely purifies the salt. Like changes occur when bone-spirit is employed. Comp. Chemically considered, this salt consists of equal VOLUMES of gaseous ammonia and hydrochloric acid gas condensed into the solid form; or, by WEIGHT , according to the ammonia-theory, of— | Atoms. | Equiv. wt. | Per cent. | | Ammonia (NH3) | 1 | 17· | 31·78 | | Hydrochloric acid (HCl) | 1 | 36·5 | 68·22 | | —— | ——— | ——— | | Hydro chlorate of Ammonia (NH3HCl) | 1 | 53·5 | 100· | Or, according to the ‘ammonium-theory,’ of— | Atoms. | Equiv. wt. | Per cent. | | Ammonium (NH4) | 1 | 18· | 33·65 | | Chloride (Cl) | 1 | 35·5 | 66·35 | | —— | ——— | ——— | | Chloride of Ammonium (NH4Cl) | 1 | 53·5 | 100· | Prop. . The sal ammoniac of commerce is found under the form of large white hemispherical, cup-like cakes or ma es (or in large fragments which are sections of them), po e ing a tough, fibrous, semi-crystalline texture, and very difficult to powder. It is odourle , has a saline taste somewhat sharp or acrid, and sublimes without either fusion or decomposition. It slightly reddens litmus; di olves in rather le than 3 parts of cold water, and in about 1 part of boiling water; is soluble in alcohol; and when crystallised from water, under favorable circumstances, forms distinct octahedra, or cubes, usually small and aggregated together in rays or feathery ma es. By slowly evaporating its aqueous solution, it may be sometimes obtained in cakes an inch in thickne . It is anhydrous. Sp. gr. 1·450. Pur. It should give a colourle solution with water; wholly sublime with heat; and neither chloride of barium, nor sulphuretted hydrogen, should affect its solution. A solution, to which a few drops of nitric acid have been added, should not yield a blue precipitate with ferrocyanide of pota ium. It often contains sesquichloride of iron, and sometimes lead; both of which may be readily detected by the above tests. Its complete volatility may be easily determined by heating, in the flame of a candle, a small fragment held on the point of a knife. Tests. —1. It is known to be a salt of ammonium by its cooling ammoniacal fumes when triturated with lime, or when moistened with caustic pota a or soda:—2. It is shown to be a chloride by its solution yielding, with nitrate of silver, a white curdy precipitate, insoluble in boiling nitric acid, soluble in ammonia. Uses, . In the arts , chiefly in the coating and soldering of metals, and the preparation of alloys; in dyeing; and in the manufacture of ammonia-alum; also, in large quantities, to give a factitious pungency to snuff. In chemistry , as a reagent; and, owing to the cold produced during its solution, to form frigorific mixtures. In medicine it is chiefly used externally, as a stimulant and resolvent or discutient; and occasionally, internally, as a diuretic, stimulant, resolvent, alterative, tonic, ., particularly in chronic inflammations of the mucous and serous membranes, in chronic glandular and visceral enlargements and indurations, and in amenorrhœa. In rather large doses, frequently repeated, it is said to prove often highly beneficial in chronic enlargement and induration of the prostate gland (M. René Vanoye); and also in other like cases.— Dose , 5 to 20 gr., 3 or 4 times daily, either in powder or solution, mixed with some demulcent; as a discutient or resolvent lotion, 1 to 1 1 ⁄ 2 oz., to 1 ⁄ 2 pint of water, either with or without 4 or 5 fl. oz. of spirits or strong vinegar (often serviceable in chilblains); as a weak lotion, or a collyrium or injection, 1 to 4 dr., to water, 1 pint. In very large doses it is poisonous; the treatment is emetics and mucilaginous or demulcent drinks. Concluding remarks, Patents, . The methods already described are those by which commercial hydro chlorate of ammonia is usually if not almost entirely obtained; the various improvements or modifications, from time to time introduced, affecting chiefly the minor details, and the form or size of the apparatus and machinery employed, and not the general principles on which the proce es are based. One of the most important of these has for its object the entire removal of the iron present in the crude salt, some of which, if it be not removed before sublimation, is volatilised and contaminates the ultimate product. To obviate this evil, Mr Brewer pa es a few bubbles of chlorine through the hot concentrated solution of the salt, previous to its crystallisation; by which the pro to chloride of iron is converted into the perchloride, which, being acted on by the ammonia always present in the liquor, is precipitated as ferric hydrate, with the formation of a small additional quantity of sal ammoniac. The only precaution nece ary is to avoid employing more chlorine gas than is nece ary to peroxidise the iron; as beyond this a portion of the ammonia-salt itself is decomposed, with the evolution of nitrogen. The temperature of the liquor is kept up, after the action of the chlorine, until the whole of the brown flocculent oxide of iron has subsided, when it is at once decanted or filtered into the crystallisers. Another modification which has been adopted in two or three places is to effect neutralisation of the crude ammoniacal liquor by distilling it, and pa ing the fumes in at the lower end of a hollow shaft or column filled with coke, down which the acid trickles; the resulting solution of sulphate or chloride of ammonium being received in proper cisterns, conveniently situated near the base of the column. In Mr Spence’s method of obtaining ammonia-salts from gas-liquor or bone-spirit, a series of (usually four) cylindrical boilers, or reservoirs, so placed that the contents of each upper one may be drawn off into the one next below it are employed. Each boiler has an exit-pipe which carries the vapour generated in it to that next above it, whilst that of the highest boiler pa es off to a trunk containing the acid nece ary to form the salt. The top boiler is connected with the reservoir of gas-liquor (which is already mixed with milk of lime) by a charging pipe furnished with a stop-cock turned by a floating ball, so as to keep the surface of the liquor constantly at the same height. High-pre ure steam enters the lower boiler, by which its ammonia is driven through the connecting pipe into the next boiler, and so on in succe ion, until it leaves the highest boiler in a concentrated state, and thus enters the acid-tank. When this last contains moderately strong hydrochloric or sulphuric acid, the resulting solution of CHLORIDE or SULPHATE OF AMMONIUM (as the case may be) is sufficiently concentrated to be at once run off into the crystallisers. As soon as the liquor in the lowest boiler is exhausted of its ammonia, its contents are drawn off, and replaced by that of the next boiler, which is followed by a like descent throughout the whole series. Among improvements having for their object the substitution of cheap chlorides [52] for the more expensive commercial acids, may be mentioned those of— [52] Particularly such chlorides as are the ‘waste or bye products’ of other manufactures. 1. Mr Laming (Patent dated 1843), who employs a strong solution of CHLORIDE OF CALCIUM for converting the ammonia of gas-liquor into the hydro chlorate. 2. Mr Hills (Patent dated 1846) employs CHLORIDE OF MAGNESIUM [53] in the same way; and by a subsequent patent proposes to convert the ammonia eliminated in the distillation of coal into the hydro chlorate, by mixing CHLORIDE OF MAGNESIUM with the coal in the retorts, or by introducing the chloride into a retort appropriated for the purpose. The heat dispels the chlorine of the chloride, in the form of hydrochloric acid, and this, uniting with the ammoniacal vapour, forms hydro chlorate of ammonia, which is retained in the liquor of the condenser. From this liquor the salt is obtained by evaporation, ., in the usual way. [53] Of the Epsom-salt works, . 3. Mr Croll (Patent dated 1849) converts the crude ammoniacal vapours that i ue with the gas from the common retorts into the hydro chlorate, and obtains a solution of it by pa ing the gas through a solution of crude CHLORIDE OF MANGANESE [54] (1 cwt. of the salt to about 40 galls. of water), contained in one of the ordinary ve els used for purifying coal-gas. The manganic solution absorbs the ammonia and its salts, converting them into the hydro chlorate, whilst a corresponding proportion of oxide of manganese is precipitated. As soon as the liquor in the purifier is fully saturated, it is drawn off, and replaced by a fresh quantity; whilst the saturated liquor containing the hydro chlorate, after subsidence, or filtration, is evaporated, ., as before. Crude CHLORIDE OF IRON may be substituted for the chloride of manganese, in the above proce : as may also SULPHATE OF MANGANESE , but then the product, of course, will be sulphate of ammonia, instead of the hydro chlorate. [54] Obtained from the chloride-of-lime works. The portion of the precipitated oxide of manganese saved from the proce may be reconverted into the chloride, by mixing 3 parts of it with 4 parts of common salt, and heating the mixture to low redne , scarcely perceptible in the dark, for 2 to 3 hours. 140 lbs. of the calcined ma , with 40 galls. of water, forms a solution that may be again pumped into the purifier. 4. Mr Laming (Patent dated 1850) also proposes the use of various salts and mixtures for retaining and condensing the ammoniacal vapour of coal-gas as it pa es from the retorts through the purifiers. Of these the principal are CHLORIDE OF CALCIUM obtained by decomposing chloride of iron by hydrate of lime; CHLORIDE OF IRON , obtained by decomposing sulphate of iron with chloride of sodium; CHLORIDE OF MAGNESIUM ; a mixture of SULPHATE OF LIME and SULPHATE OF IRON ; or of moist precipitated oxide of iron with carbonate of lime, carbonate of magnesia, or magnesian limestone; or one containing sulphate of magnesia, or chloride of magnesium or calcium, or one or more of them, in combination with oxide of copper, either with or without lime or magnesia, or with both or either of them or their carbonates. These salts, or compounds, are mingled with sawdust, or some other porous substance not acted on by the gas, before being put into the purifiers; and after they become saturated with the vapour, the newly-formed hydro chlorate or sulphate (according to the salt or mixture employed) is washed out of the ma with water. Besides the usual sources of SAL AMMONIAC (and the other ammonia-salts of commerce) it has been proposed to obtain it from guano, peat, shale, ., as noticed under Sesquicarbonate of Ammonia ( suprà ); the substance employed to effect the neutralisation or decomposition of the ammoniacal liquor being, in this case either hydrochloric acid or a chloride. In Young’s Patent (1841) for ‘obtaining AMMONIA and its SALTS ,’ a mixture of 2 parts of guano, and 1 part of hydrate of lime, is distilled in a retort placed vertically, at a moderate heat, gradually increased until the bottom of the retort becomes red hot. The ammoniacal portion of the fumes evolved are absorbed by the cold water contained in a suitable condenser; whilst the other gases eliminated by the proce pa off uncondensed. By subsequently pa ing carbonic acid gas into the liquor of the condenser, a solution of CARBONATE , BICARBONATE , or SESQUICARBONATE of AMMONIA is formed. By nearly filling the condenser with diluted hydrochloric or sulphuric acid, instead of with water, a solution of HYDRO CHLORATE or of SULPHATE of AMMONIA is obtained. Stale urine saturated with hydrochloric acid, or with sulphuric acid diluted with about twice its weight of water, yields SAL AMMONIAC , or SULPHATE OF AMMONIA (according to the acid used) on evaporation. Hydro chlorate of ammonia is now wholly prepared on the large scale, and never by the dealer or retailer, by whom it is only occasionally refined or purified, in small quantities, for chemical and medical purposes. The sal ammoniac of commerce is found to be sufficiently pure for all its ordinary applications in the arts; but when wanted of greater purity, it is broken into pieces, and resublimed from an earthenware ve el into a large receiver of earthenware or gla . The product ( REFINED SAL AMMONIAC , DOUBLE-REFINED S. A. ; AMMONIÆ HYDROCHLO′′RAS PU′′RA , SAL AMMONI′ACUS DEPURA′TUS †, L.) is popularly known as FLOWERS OF SAL AMMONIAC (flo′res sa′lis ammon i′aci, L.), from being in a finely divided crystalline state. The chemically pure chloride of ammonium may be prepared by bringing its gaseous constituents—ammonia and hydrochloric acid—into contact. During the combination much heat, and even light, is generated, and the anhydrous solid salt is precipitated in a minutely divided state, which, under the microscope, is seen to be crystalline. It may be also more easily and conveniently prepared by saturating pure and moderately dilute hydrochloric acid with ammonia or its carbonates, and evaporating the solution until a pellicle forms, when crystals of the chloride separate as the liquid cools. A similar but rather more violent reaction occurs when gaseous chlorine is brought in contact with gaseous ammonia, or is pa ed into a nearly saturated solution of ammonia or its carbonates; but in this case nitrogen is evolved at the expense of the ammonia; moreover, the proce is attended with danger. The manufacture of sal ammoniac is usually a distinct busine , and is carried on to a very great extent in the neighbourhood of London. Indeed, the London makers now supply the chief portion of that used in England. A large quantity is now, however, made at Manchester and Liverpool. A small quantity is imported from Germany. That from Brunswick is in the form of sugar-loaves. An inferior quality is also imported, in chests, from the East Indies. The red bands frequently seen in the sal ammoniac of commerce are said to arise from the workmen falling asleep, and allowing the fire to go down, and then suddenly raising the heat too high. (Muspratt.) They consist chiefly of ammonio-chloride of iron.