Cooley's Cyclopaedia of Practical Receipts Volume I Part 40

[Ill.u.s.tration]

The crude dried salt of the last process 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 f.l.a.n.g.e 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 dissipated 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 progress made; the fires having been purposely neglected or checked for some hours previously. The process 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 lessen the purity and beauty of the product. The unsublimed portion in the pots forms a conical ma.s.s, 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.

[Ill.u.s.tration]

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 HYDROCHLORATE OF AMMONIA at once removed. These vary from 2 to 5 inches in thickness, 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 sc.r.a.ped, 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 process 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 hydrochlorate. It is intimately mixed with about an equal weight of chloride of sodium (common salt) before being put into the sublimers.

[Footnote 49: Sp. gr. 133 to 138.]

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 hydrochlorate, during the process, by the addition of chloride of sodium. Both these last methods are described below.

2. From BONE-LIQUOR, &c.[50]--The ammoniacal liquor technically called 'bone-liquor' or 'bone-spirit,' and formerly known under the name of 'spirit of hartshorn,' is essentially a solution of carbonate of ammonia more or less 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 processes closely resemble those already described, except in being less troublesome, owing to the absence of the tarry and other foreign matters which impede and complicate them when gas-liquor is employed.

[Footnote 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, sc.r.a.pings of hides, leather cuttings, &c.) is employed for the same purpose. The preparatory process by which this liquor is obtained is essentially 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.s.sium and Prussian blue. These liquors have usually a density ranging between 8 and 9 Baume (Ure; = sp. gr. 1056 to 1063).]

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.s.sed 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-c.o.c.k. 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.s.sed 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.s.sed 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. 1160. Chloride of sodium (common salt), in sufficient quant.i.ty to convert all the sulphate of ammonia in the liquid into hydrochlorate, 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, sc.r.a.ped 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.s.s 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 HYDROCHLORATE 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 vessels are set on the dome of a furnace, which is perforated with holes or slits, to allow the heat to pa.s.s 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 vessels, 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 process 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.s.s, with which each of the iron pots are capped."[51]

[Footnote 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, &c., 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 (NH_{3}) 1 17 3178 Hydrochloric acid (HCl) 1 365 6822 --- ----- ------ Hydrochlorate of Ammonia (NH_{3}HCl) 1 535 100

Or, according to the 'ammonium-theory,' of--

Atoms. Equiv. wt. Per cent.

Ammonium (NH_{4}) 1 18 3365 Chloride (Cl) 1 355 6635 --- ----- ------ Chloride of Ammonium (NH_{4}Cl) 1 535 100

_Prop. &c._ The sal ammoniac of commerce is found under the form of large white hemispherical, cup-like cakes or ma.s.ses (or in large fragments which are sections of them), possessing a tough, fibrous, semi-crystalline texture, and very difficult to powder. It is odourless, has a saline taste somewhat sharp or acrid, and sublimes without either fusion or decomposition. It slightly reddens litmus; dissolves in rather less 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 circ.u.mstances, forms distinct octahedra, or cubes, usually small and aggregated together in rays or feathery ma.s.ses. By slowly evaporating its aqueous solution, it may be sometimes obtained in cakes an inch in thickness. It is anhydrous.

Sp. gr. 1450.

_Pur._ It should give a colourless 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.s.sium. 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.s.sa 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, &c._ 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 quant.i.ties, to give a fact.i.tious 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, &c., particularly in chronic inflammations of the mucous and serous membranes, in chronic glandular and visceral enlargements and indurations, and in amenorrha. In rather large doses, frequently repeated, it is said to prove often highly beneficial in chronic enlargement and induration of the prostate gland (M. Rene 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, &c._ The methods already described are those by which commercial hydrochlorate 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 processes 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.s.ses a few bubbles of chlorine through the hot concentrated solution of the salt, previous to its crystallisation; by which the protochloride 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 quant.i.ty of sal ammoniac. The only precaution necessary is to avoid employing more chlorine gas than is necessary 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.s.sing the fumes in at the lower end of a hollow shaft or column filled with c.o.ke, 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.s.ses off to a trunk containing the acid necessary 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-c.o.c.k turned by a floating ball, so as to keep the surface of the liquor constantly at the same height. High-pressure steam enters the lower boiler, by which its ammonia is driven through the connecting pipe into the next boiler, and so on in succession, 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 subst.i.tution of cheap chlorides[52] for the more expensive commercial acids, may be mentioned those of--

[Footnote 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 hydrochlorate.

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 hydrochlorate, 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 hydrochlorate of ammonia, which is retained in the liquor of the condenser. From this liquor the salt is obtained by evaporation, &c., in the usual way.

[Footnote 53: Of the Epsom-salt works, &c.]

3. Mr Croll (Patent dated 1849) converts the crude ammoniacal vapours that issue with the gas from the common retorts into the hydrochlorate, and obtains a solution of it by pa.s.sing 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 vessels used for purifying coal-gas. The manganic solution absorbs the ammonia and its salts, converting them into the hydrochlorate, 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 quant.i.ty; whilst the saturated liquor containing the hydrochlorate, after subsidence, or filtration, is evaporated, &c., as before. Crude CHLORIDE OF IRON may be subst.i.tuted for the chloride of manganese, in the above process: as may also SULPHATE OF MANGANESE, but then the product, of course, will be sulphate of ammonia, instead of the hydrochlorate.

[Footnote 54: Obtained from the chloride-of-lime works. The portion of the precipitated oxide of manganese saved from the process may be reconverted into the chloride, by mixing 3 parts of it with 4 parts of common salt, and heating the mixture to low redness, scarcely perceptible in the dark, for 2 to 3 hours. 140 _lbs._ of the calcined ma.s.s, 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.s.ses from the retorts through the purifiers. Of these the princ.i.p.al 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 hydrochlorate or sulphate (according to the salt or mixture employed) is washed out of the ma.s.s 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, &c., as noticed under SESQUICARBONATE OF AMMONIA (_supra_); 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 process pa.s.s off uncondensed. By subsequently pa.s.sing 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 HYDROCHLORATE 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.

Hydrochlorate 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 quant.i.ties, 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 vessel into a large receiver of earthenware or gla.s.s. The product (REFINED SAL AMMONIAC, DOUBLE-REFINED S. A.; AMMONIae HYDROCHLO"RAS PU"RA, SAL AMMONI'ACUS DEPURA'TUS, L.) is popularly known as FLOWERS OF SAL AMMONIAC (flo'res sa'lis ammoni'aci, L.), from being in a finely divided crystalline state.

The chemically pure chloride of ammonium may be prepared by bringing its gaseous const.i.tuents--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.s.sed 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 process is attended with danger.

The manufacture of sal ammoniac is usually a distinct business, 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 quant.i.ty is now, however, made at Manchester and Liverpool. A small quant.i.ty 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.

=Ammonium, Citrate of.= (NH_{4})_{2}HC_{6}H_{6}O_{7}. _Syn._ DIAMMONIUM CITRATE, CITRATE OF OXIDE OF AMMONIA; AMMON"NIae CIT'RAS, L.

_Prep._ A concentrated solution of pure citric acid, gently heated, is saturated with sesquicarbonate of ammonium, in fine powder (about 7 parts to 6), and slightly in excess; and the resulting liquid is crystallised by refrigeration in close vessels, or by evaporation in vacuo. If heat be employed in the evaporation of the solution, an acid citrate will be formed.

_Uses, &c._ Chiefly as a chemical test. An extemporaneous citrate, made with lemon-juice and drunk effervescing, is employed as a saline draught, and a mild aperient and diaph.o.r.etic, in fevers, &c.

=Ammonium, Ferrocyanide of.= (NH_{4})_{4} FeC_{6}N_{6} . 3Aq. _Syn._ FERROCYANATE D'AMMONIAQUE, Fr. _Prep._ 1. Saturate a solution of hydroferrocyanic acid with sesquicarbonate of ammonium, in slight excess; evaporate the solution at a heat below ebullition, and crystallise by refrigeration.