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Chloride of Sodium, muriate of soda or common | is, obtained from Barilla, the ashes of plants soda-is found in immense quantities in the earth growing on the seashore; the ashes of the Salsola as rock salt. The mines of Cheshire and Worcester- clavifolia yielding about 46 per cent., and the shire in this country, and those of Poland, Hun- Salsola soda about 41 per cent. of their weight of gary, Spain, and many other places, may be said this salt. Kelp, the ashes of sea-weeds, contains to be inexhaustible. Actual mining of salt is a notable proportion of carbonate of soda, but little practised with us. The water near the salt is valuable only as a source of iodine and potash. is saturated brine, which is purified up and evapo- However, the quantity annually derived from rated in pans 30 to 60 feet long. The soil around these sources is very trifling when compared with Northwich is in many places much depressed by the quantity manufactured from common salt. this, and the town itself is a constant succession of risings and fallings. It is also obtained in large quantities by the evaporation of sea water. In warm countries this is carried on in pits dug in the beach by the heat of the sun's rays, leaving the common salt, mixed with various salts of magnesia and lime, as a white incrustation. In colder climates the evaporation is conducted in iron pans on the sea shore, by the aid of fuel. The salt crystallises out, the crystals are then drained from the mother liquor, which is called bittern, and are ready for the market. Basket salt is made by placing the crystals obtained in the above process in conical baskets, and washing them with a saturated solution of salt, which dissolves and carries off any magnesia or lime salts.

In Cheshire, the mine salt has been sold, in 1863, at the pit mouth at even less than half-a-crown per ton. The large crystals used for soda are obtained from the pans at 4s. a ton. That salt which is rapidly evaporated with the fire is fine, and sold as salt. It contains a little sulphate of lime. The coarser salt is formed less rapidly, and the very large crystals, which appear ornamental rather than useful, are formed singly in quiet portions of the pan. They are in reality the purest.

Pure salt should not become sensibly moist on exposure to the air; it decrepitates when suddenly heated. Salt is employed extensively in the production of sulphate of soda, to be afterwards converted into carbonate of soda by Le Blanc's process. At the present time (1865), 350,000 tons of salt are annually consumed in this country in this one branch of industry. It is also largely used in many other chemical and metallurgical operations, and for the preservation of animal food. Common salt is an excellent antiseptic.

The process now generally employed for the manufacture of carbonate of soda from common salt is substantially that recommended by Le Blanc in 1792, and consists first in the decomposition of the salt by sulphuric acid, as described above, and afterwards roasting the sulphate of soda so obtained in reverberatory furnaces with a mixture of lime or chalk and small coal, the proportions being two parts of sulphate of soda, two parts limestone or chalk, and one part small coal; the mixture melts into a pasty mass termed black ash,' which on being withdrawn from the furnace, cooled, and lixiviated with cold water, yields a solution containing principally carbonate of soda. The insoluble residue consists of a sulphate of calcium mixed with carbonate of lime &c., and is known as blue waste, vat refuse, or soda waste.

The solution containing carbonate of soda is evaporated to dryness, mixed with a small proportion of sawdust, and calcined at a moderate temperature. The product thus obtained is called soda ash, and contains from 44 to 50 per cent. of alkali.

Soda Crystals or Washing Soda.-This is obtained by dissolving the soda ash in water, evaporating, and crystallising in iron pans.

Carbonate of soda is also manufactured from Cryolite, a mineral found in West Greenland and also in the Ural mountains; it is a double fluorite of aluminium and sodium. The mineral is ground to powder, mixed with its own weight of lime, and either calcined, or mixed with as much water as will form a milk, and boiled for some time. Fluoride of calcium remains insoluble while aluminate of soda is dissolved by the water. On passing carbonic acid gas through the liquid the alumina is precipitated, and carbonate of soda is formed and may be obtained in crystals on evaporation. One ton of cryolite will yield from 14 to 2 tons of soda crystals. The quantity of cryolite

about 3,000 tons, the greater portion of which is sent to Copenhagen, and the remainder to Boston, U. S.; at both of which places the above processes are carried on.

Sulphate of Soda or Glauber's Salts.-This is prepared by heating together a mixture of sulphuric acid and common salt; muriatic or hydro-annually obtained from Greenland is stated to be chloric acid is evolved and condensed in Wolfe's bottles on a small scale, or in vessels filled with coke or bricks on a large scale, while sulphate of soda remains in the retort. Sulphate of soda is also obtained as a residue in the preparation of nitric acid from nitrate of soda, and is found pretty extensively in various parts of the world, more particularly in Spain and South America. It exists in almost all waters; the mineral springs of Cheltenham and Leamington owe their purgative properties to its presence. Crystallised sulphate of soda is often found as an efflorescence upon plaster and brick-work in damp situations.

Sulphate of soda, when in crystals, is remarkably efflorescent, losing the whole of its water of crystallisation, at ordinary temperatures, on mere exposure to the atmosphere.

A convenient freezing mixture may be made by pouring five parts commercial hydrochloric acid upon eight parts of the crystallised sulphate. Carbonate of Soda.-This is found native in several localities; in some places, Egypt, and fer instance Hungary, being left as an incrustation when the so-called soda lakes' dry up in the summer; in other places, Hungary &c. it exudes from the ground. A considerable quantity of carbonate of soda was formerly, and indeed still

Carbonate of soda has also been obtained from soda felspar, but not to any considerable extent.

Soda ash and soda crystals are both very largely used in many industrial and chemical operations, more particularly in the manufacture of soap, and in dyeing and scouring.

In this country upwards of 300,000 tons of carbonate of soda are annually made. It is exported largely.

Bi-carbonate of Soda.-This is procured by exposing the crystallised carbonate to an atmosphere of carbonic acid. The crystals absorb the carbonic acid, and at the same time lose their water of crystallisation, crumbling down into a white powder. It is used in medicine, in the production of effervescing drinks, baking powders &c. On being subjected to a red heat it loses half of its carbonic acid, and is converted into the anhydrous simple carbonate.

Caustic Soda.-This may be prepared from the soda ash of commerce by boiling with an excess of fresh slaked lime. Insoluble carbonate of lime is formed, and caustic soda remains in solution; the

clear liquid is decanted, evaporated, fused, and, while still liquid, is run into iron casks, and when cold is ready for market.

The mother liquors from the manufacture of soda crystals are now generally used for the production of caustic soda. As they always contain a considerable amount besides carbonate, they are well suited for the purpose.

Caustic soda is daily becoming of more importance in the arts; large quantities are used for making soap, and for bleaching, scouring, dyeing. The commercial product generally contains from 60 per cent. to 70 per cent. of alkali.

Nitrate of Soda, Cubic Nitre, or Chili Saltpetre -is largely imported into this country, and is used as a source of nitric acid, also in the manufacture of nitrate of potash by double decomposition with chloride of potassium, and in manure. It is somewhat deliquescent. When heated to 591° Fahr. it fuses, and on exposure to a higher temperature suffers decomposition.

The following interesting account of the production of the nitrate beds in South America is extracted from the report of Mr. Salidan, late her Majesty's consul at Lima :—

"The amount of exports in British ships, in 1864, were, 31,098 tons, of the value of 865,465 dollars." Sulphite of Soda or Antichlor. It is prepared by passing sulphurous acid gas, obtained by the combustion of sulphur in air, into a solution of carbonate of soda, and crystallising. This salt was formerly used for removing the last traces of chlorine from the bleached pulp in the manufacture of paper, but is now to a great extent superseded by hyposulphate of soda.

Hyposulphite of Soda.-This may be readily prepared by digesting the above-mentioned salt with flowers of sulphur, evaporating, and crystallising. It may also be prepared from the soda waste produced in the manufacture of soda ash. Hyposulphite of soda is largely used by photographers for dissolving the undecomposed salts of silver. It is calculated that the quantity used in England alone for this purpose is not less than 200 tons per annum, while a far larger quantity is used by the paper manufacturers,

Phosphate of Soda.-Common tribasic phosphate of soda is prepared on a scale of some magnitude by treating powdered bone ash with dilute sulphuric acid, rendering slightly alkaline with carbonate of soda, filtering from the insoluble carbonate, phosphate and sulphate of lime, and crystallising. This salt is used in medicine. It also

used by calico printers. There are several other phosphates of soda, but they are of no importance in commerce.

Iquique is the centre of the nitrate of soda trade, and to this article alone it owes its present position. The population of the province is estimated at 15,000, four-fifths of whom are more or less inter-enters into the composition of the dunging liquors, ested in it. Large and apparently inexhaustible beds of this and other salts are found in the pampa or plain of Iamarugal, say between the Valley of Camarones on the north, and the river Lox (the boundary line of Peru and Bolivia) on the south, a distance of over 150 miles, lying principally towards the Western side, distant from the shipping port from 6 to 12 leagues. The beds of nitrate, or calisheras, are insulated deposits, very irregular, some on the plain, others on the rising ground, varying much in size and shape, and in depth, beneath the surface crust of earth and clay, from 1 inch to many feet, and in thickness from 6 inches to as many feet. Amongst the other salts found in their vicinity may be enumerated carbonate and sulphate of soda, biborates of lime and soda, magnesium-alum, chlorate of sodium. Traces of iodine exist in the nitrate, and in most of the waters in the plain have been discovered traces of boracic acid.

Its cost at the works varies from 61 reales to 84 reales per quintal, according to the aptitude of the labourers, and the distance they may have to send for water and fuel. The rate of carriage to the coast also varies from 5 to 7 reales per quintal.

The average rate now paid for nitrate placed on the beach is 14 reales, and this would give the makers reale per quintal profit. Nitrate of soda is always sold deliverable alongside the ship's launch outside the surf. The merchant has to bag and embark it, which costs him about 14 reale per quintal, therefore selling at 17 reales would yield lim 14 per quintal profit.

The wages now given are, to the barretero (miner) and fondeador (boiler of the nitrate) 1 real of the quintal produced, each ; to the acendrador (who breaks the nitrate and separates the refuse) real per 2 quintals; to other labourers from 1 dollar 4 cents, to 2 dollars per day.

"The principal shipping places are Iquique, Patillos, Mexillones, and Pisagua.

"The total amount exported since the year 1830, when the trade was commenced, is :

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quintals

361,385
761,349

1,592,306

2,060,595

3,260,473

8,036,108

Bi-borate of Soda or Borax (Sohaga, Tincal, Indian names)-obtained in large quantities in the valley of Puga, in Ladahk, and at Thibet, is collected on the borders of the lakes as the water dries up; it is then smeared with fat to prevent loss by exportation, and transferred across the Himalayas on the backs of sheep and goats. It is refined at Umritsur and Lahore by washing with lime water. It is employed medicinally by the natives as a tonic, deobstruent, and diuretic. It is also obtained in California. It is obtained in the crude state by the evaporation of the waters of the lake whence it is derived, and is purified by dissolving in water, rendering slightly alkaline with carbonate of soda (to precipitate earthy salts), filtering and crystallising. Artificial borax is prepared largely by dissolving the boracic acid obtained from the lagoons of Tuscany in carbonate of soda or caustic soda, filtering, and crystallising slowly. In some works the crude boracic is mixed with soda potash and calcined at a low heat; the fritted mass is then lixiviated with water, and the clear solution evaporated and crystallised.

A native borate of lime and soda is found in large quantities in Peru; it is used for the preparation of boracic acid and borax.

Borax is obtained crystallised in two varieties, octahedral and prismatic, the former containing 30-8 per cent, water, and the latter 47°2 per cent. Both varieties, when exposed to the action of heat, lose the whole of their water, and melt below redness to a transparent colourless glass, which possesses the property of dissolving many of the metallic oxides, often with characteristic colours; hence it is much used in the laboratory as a blowpipe reagent. Borax is used in the arts as a flux, and by the refiner in the melting of gold and silver; it is also valuable for facilitating the soldering and welding of metals. In making enamels it is frequently added for the purpose of rendering the compound more fusible, and it is largely employed in fixing colours on porcelain; borax is also used in medicine

Silicate of Soda or Water Glass-is prepared by igniting 45 lbs. powdered quartz with 23 lbs.

Potash alum-is a double sulphate of potash and alumina.

anhydrous carbonate of soda and 3 lbs charcoal; | flux in cases where the action of an acid at a high or, according to Buchner, it may be prepared more temperature is required. cheaply from sulphate of soda, and in the proportion of 100 parts quartz, 60 parts anhydrous sulphate of soda, and 15 to 20 parts charcoal dust. After cooling, the vitreous mass is broken up and boiled with water for three or four hours, the water being replaced as it evaporates. When the whole is dissolved the solution is concentrated till it attains the specific gravity of from 1-24 to 1-26. In this state it is sufficiently liquid to be used for some purposes, for others it may be evaporated to a syrupy consistence.

The most important uses of silicate of soda are for hardening and preserving stones, preparing artificial stones, cement, &c. and for the preparation of colours for mural painting; it is also used by calico printers and paper makers, and in the preparation of printing ink, &c.

Aluminate of Soda.-This is used as a mordant for fixing madder colours in calico printing. It is generally prepared by adding caustic soda to a solution of alum until the precipitate at first formed is re-dissolved; prepared in this manner it contains a large quantity of sulphate of soda. It is obtained tolerably pure as an intermediate | product in the manufacture of carbonate of soda from cryolite.

Stannate of Soda.-It is extensively used in dyeing and calico printing: it is prepared in a great variety of ways, generally by fusing tin or tin-ore with soda or a salt of soda.

Arseniate of Soda.-This is also used largely in calico printing dunging liquor.' One method is to heat arsenic with nitrate of soda.

Tungstate of Soda.- Prepared by fusing the ore with carbonate or sulphate of soda. Tungstate of soda is used in dyeing, as a mordant, in the same manner as stannate of soda: it has lately acquired considerable importance as a medium for rendering linen, cotton and other fibrous substances non-inflammable; for this purpose it is used in solution, either alone or in conjunction with phosphate of soda.

Fluoride of Sodium and Aluminium.-This is found native as Cryolite in Greenland, and in the Ural mountains; used as a source of carbonate of soda, also of aluminium.

Acetate of Soda-is prepared in large quantities during the purification of acetic acid; the crude acid obtained by the distillation of wood is neutralised by carbonate of soda or soda ash, and the salt thus obtained purified by crystallisation.

Potash or Vegetable Alkali.-Extensively distributed in the vegetable and mineral kingdoms; it is also present in animal juices, and in all fertile soils. Potassium.-The metal of which potash is an oxide is prepared precisely in the same manner as sodium, substituting for the carbonate of soda the corresponding salt of potash. This metal is not nearly of as great importance in commerce as sodium, and is much more expensive. The properties of both are very similar.

Chloride of Potassium.-Large beds of this salt have been lately discovered at Stassfurt in Prussia, along with common salt and chloride of magnesium. It is also extracted in considerable quantity from 'kelp,' the ashes of sea-weeds, and is used largely in the manufacture of potash alums, in the preparation of the other salts of potash, and in manure. Bi-Sulphate of Potash.-Obtained on a large scale as a residuary product in the manufacture of nitric acid from nitrate of potash; it is the sal enisum of the older writers. It is very soluble in water, the crystals fuse below a red heat, and on prolonged ignition are converted into the simple sulphate. The bisulphate is sometimes used as a

Carbonate of Potash, Potashes, and Pearlashes.— Carbonate of potash is obtained in large quantities for commercial purposes by lixiviating wood ashes, evaporating and crystallising; the mother liquor, containing the carbonate of potash, is evaporated to dryness, yielding the potashes of commerce, and these when calcined constitute what is known as pearlash. Commercial potashes generally contain from 50 to 60 per cent. of alkali. Carbonate of potash is also obtained by decomposing the chloride and sulphate, as in the preparation of carbonate of soda from common salt; and from felspar, by exposing an intimate mixture of 100 parts, with about 150 parts lime, to a white heat, boiling the mass with water, and saturating the solution so obtained with carbonic acid, to precipitate silica and alumina; the clear liquid contains the mixed carbonates of potash and soda; on evaporation the carbonate of soda crystallises out, leaving the carbonate of potash in solution. Mr. F. O. Ward heats the felspar with fluorspar and lime. It has been found remunera tive to extract potash from the grease taken from the wool of sheep; 1000 lbs. of wool yield about 80 lbs. carbonate of potash free from soda; also from the juice of the sugar beet in France.

Carbonate of potash is largely used in the arts, particularly in the manufacture of soap and glass, and for preparing caustic potash and its salts.

Bi-carbonate of Potash is prepared by passing a current of carbonic acid gas through a strong solution of the carbonate of potash; crystals of the bicarbonate are deposited. This salt is consumed medicinally in considerable quantities.

Caustic Potash is procured from its carbonate in precisely the same manner as caustic soda.

Nitrate of Potash, Saltpetre, or Nitre.-The principal supply of this important salt is derived from various districts in the East Indies, where it occurs sometimes as an efflorescence, at other times disseminated through the soil itself. For its formation it is necessary that the soil should contain felspar or other mineral yielding much potash. The nitre is extracted from the soil by lixiviation with water; evaporating the solution so obtained, removing any common salt which may fall, and crystallising; the crystals being purified by repeated re-crystallisations.

Nitre may be also made artificially in beds of decaying vegetable or animal substances, mixed with old mortar, or other refuse calcareous earth; these are watered occasionally, too much moisture being hurtful; after a certain period, depending on the rapidity with which the process has gone on, the whole is submitted to lixiviation together with wood-ashes; which contain carbonate of potash, and which decompose any nitrate of lime formed, of which there is generally a considerable quantity. After the lixiviation is complete, which takes some time, the solution is separated and boiled down; the common salt separates as in the other process, and the nitre is then crystallised. It was from this source that the whole of the nitre, nearly, employed by the French during the long protracted war with the continental powers was obtained, as in former times in this country when the obnoxious Petremen collected it.

Nitre is now manufactured largely from nitrate of soda, by double decomposition with chloride of potassium; chloride of sodium and nitrate of potash are formed, and are separated by crystallisation. 85 of nitrate of soda are mixed with 74 of chloride of potassium.

Bichromate of potash is extensively used in dyeing and calico-printing, in preparing pigments, and in bleaching tallow, palm oil, &c. It is soluble in ten times its weight of cold water.

Iodide of Potassium-is obtained by dissolving iodine in caustic potash, evaporating to dryness, gently igniting the mass, to decompose iodate of potash, redissolving in water or alcohol, and crys tallising. It may also be obtained by digesting 2 parts iodine and one part iron filings in a stoppered vessel with ten parts water; under these circumstances iodide of iron is formed by the direct union of the metal with the iodine: the liquid is then boiled, and a solution of carbonate of potash is added in small quantities so long as a precipitate is formed, the solution is filtered from the insoluble carbonate of iron and set aside to crystallise.

Nitre has a cold, penetrating, and nauseous | turers dispense with potash in the calcination taste; enters into igneous fusion at a gentle heat, altogether, using only lime, and afterwards deand is then moulded into round cakes called sal composing the chromate of lime formed by carprunella. It is employed in the manufacture of bonate of potash. gunpowder, which is composed of 75 parts by weight of nitre, 16 of charcoal, and 9 of sulphur (the nitre for this purpose should be of great purity); as a flux it is one of the most powerful we possess; it is also used for the preservation of animal food, and in making frigorific mixtures; 1 oz, of nitre dissolved in 5 oz. of water lowers its temperature 15 degrees of Fahrenheit's thermometer. It was formerly used for procuring nitric acid and for giving nitrous fumes to the vitriol chambers, but the nitrate of soda has now taken its place in these operations. [SALTPETRE.] Chlorate of Potash-is generally prepared by passing chlorine gas into a mixture of 300 parts caustic lime, 154 parts chloride of potassium, and 100 parts water, the operation being conducted in close leaden tanks, heated by steam, and provided with agitators; when the mixture is saturated with chlorine, the liquid is filtered off and evaporated nearly to dryness, and the resulting mass redissolved in hot water, and set aside to crystal lise, the crystals being afterwards slightly washed and drained. In this process 154 parts chloride of potassium yield fully 200 parts chlorate of potash. The chlorate of potash of the best makers is a nearly pure product.

Chlorate of potash is extensively used in the preparation of lucifer matches, and in pyrotechnical mixtures. It enters into the composition used for filling percussion caps, &c., and is a convenient source of oxygen gas; 1 oz. of the salt yielding nearly 2 gallons of oxygen.

As an oxidising agent, chlorate of potash is used by the calico printer for heightening the intensity of steam colours;' and in the laboratory it is in constant request. Finally, it is of value in pharmacy, being sometimes administered in considerable doses by the physician.

Hyposulphite of Potash, Silicate of Potash, Aluminate of Potash, Stannate of Potash, Tungstate of Potash.-These salts are prepared exactly in the same manner as the corresponding salts of soda, substituting for the salt of soda, used in the preparation, a similar salt of potash. Their uses are also identical with the corresponding soda salts.

Liebig has recently proposed the following process for the preparation of iodide of potassium: 1 part of phosphorus is placed in a basin with 40 parts hot water, to which 20 parts iodine are gradually added, with frequent agitation. The resulting colourless liquid, containing phosphoric and hydriodic acids, is poured off, and milk of lime added till the mixture is alkaline; it is then filtered and boiled down to half its bulk with 12 parts sulphate of potash, and allowed to cool. A small quantity of pure carbonate of potash is then added to precipitate any lime, and the filtered solution yields on evaporation crystals of pure iodide of potassium.

Some manufacturers employ an excess of caustic alkali in order to give the crystals a certain degree of opacity; others dip the crystals into a solution of carbonate of soda, and afterwards dry them in a stove.

Bromide of Potassium.-This is prepared in a precisely similar manner to iodide of potassium. Both salts are employed in photography to a considerable extent, and in medicine.

Ferrocyanide of Potassium or Yellow Prussiate of Potash.-This important salt is formed when azotised matters are heated to redness with carbonate of potash and iron. It is manufactured on a large scale by heating dried blood, horns, parings of hides, and other animal matters conBichromate of Potash.-A great many processes taining nitrogen, with an equal weight of carhave been devised for the preparation of this salt.bonate of potash, and about one-third their weight When the native chrome-iron ore is calcined with of iron filings stirred in an iron pot. The mass an alkaline hydrate or carbonate, in presence of when treated with water yields a solution conan oxidising agent, the oxide of chromium in the taining ferrocyanide of potassium. On evaporaore is converted into chromic acid and unites with tion the salt is obtained in large lemon-yellow the alkali; thus by fusing the chrome-iron ore with crystals, which are soluble in about 4 parts of half its weight of nitre for several hours, with fre- cold water and in 2 parts of boiling water. quent stirring, a mass is obtained which, on lixiviation with water and evaporation, yields crystals of neutral chromate of potash. By dissolving the chromate of potash so obtained in water, and adding a strong mineral acid, generally nitric acid, it is converted into the bichromate; and by evaporating the solution to the crystallising point, mechanically separating the crystals of bichromate from those of the nitrate (or other potash salt), formed at same time, and recrystallising several times, the bichromate is obtained pure-large orange-red rectangular tables.

Ferrocyanide of potassium is manufactured in large quantities for use in dyeing and calicoprinting. It produces a beautiful bright blue colour, which, however, will not bear washing with alkalies or soap. It is also used in the preparation of Prussian blue. It is the source from which prussic acid, and other compounds of cyanogen, are usually obtained, but is not itself poisonous. It has a saline, bitter taste.

Ferridcyanide of Potassium or Red Prussiate of Potash.-Obtained by passing chlorine gas through a solution of the preceding salt, until the liquid The above process of preparing the chromate ceases to give a blue precipitate with perchloride may be rendered more economical by substituting of iron. The solution on evaporation yields magcarbonate of potash for a portion of nitre, and nificent ruby-red crystals, which are soluble in still more by dispensing with the nitre altogether, 2 parts cold water, and in 1 part of boiling and effecting the oxidation by means of air ad-water. Red prussiate may also be obtained by mitted into the furnace. The addition of lime is exposing powdered yellow prussiate to the action found to facilitate the oxidation. Some manufac- of a current of chlorine gas. Red prussiate is

used by dyers and calico printers for discharging the blue colour of indigo from calico; also for dyeing blue colours.

Cyanide of Potassium-may be prepared by heating to dull redness, in a covered iron crucible, a mixture of 8 parts dry yellow prussiate with 3 parts dry carbonate of potash, until the fused mass has lost its yellow colour, and ceases to give off bubbles of gas. After the particles of iron have subsided to the bottom of the crucible, the fused cyanide is poured on a cold slab, and solidifies on cooling to a milk-white mass. This salt is very deliquescent, has an alkaline reaction, and when moist emits the odour of hydrocyanic (prussic) acid. It is very poisonous. Cyanide of potassium is a powerful reducing agent, and as such is constantly used in the laboratory. Large quantities are used for the purpose of dissolving the salts of gold and silver in the processes of electrotyping; also in photography.

Sulphate of Ammonia.-It is procured from gas liquor in same manner as the chloride, by substituting sulphuric acid for muriatic. It cannot be purified by sublimation, but may be purified by recrystallisation. It is soluble in twice its weight of cold water. Sulphate of ammonia is sometimes applied to muslins and other fabrics for the purpose of preventing them from burning with flame, should they accidentally take fire. The finished goods are dipped into a solution containing 10 per cent. of the crystallised salt, and dried in a centrifugal machine.

Liquor Ammonia.-This is prepared from either of the two preceding salts by mixing them with slaked lime, heating the mass in iron retorts, and conducting the gas evolved into water. The most concentrated solution of ammonia has a specific gravity of 875, water being equal to 1.000.

Carbonate of Ammonia.-This is prepared by mixing the chloride, or sulphate, with twice its Tartrate and Bitartrate of Potash.-Bitartrate weight of chalk, and heating the mass in of potash, or cream of tartar, is, when in its crude iron retorts. The vapours of carbonate of amand impure state, called argol, and is deposited in monia are conducted into large leaden chamthe interior of wine casks during fermentation, bers, termed baloons, where they are condensed; and from this source the whole of the cream of the salt thus obtained is purified by slow sublitartar is obtained. It is generally of a very dark mation in iron pots having conical leaden covers. brown colour, but may be purified and rendered As met with in commerce carbonate of ammonia perfectly white by solution and crystallisation. is a semi-transparent, fibrous mass, having the It is employed very extensively in dyeing, hat-pungent odour of ammonia. It is used largely by making, and in the preparation of tartaric acid, confectioners in the preparation of light pastry. and many of the compounds of tartaric acid, as It is entirely dissipated during the baking, so no tartar emetic, soluble tartar, boro-tartrate of ill effect can arise from its use. It is also used potash; when heated to redness it is converted for smelling-salts. into carbonate of potash and charcoal; mixed with half its weight of nitre and thrown into a red hot crucible it forms the black flux, and with its own weight of nitre the white flux, both of which are very much employed in metallurgic operations. The tartrate is made by the addition of carbonate of potash to a solution of the bitartrate until perfectly neutral: it is used in medicine as a mild purgative.

Rochelle Salt.-A double tartrate of potash and soda.

Binoralate of Potash or Salt of Sorrel.-Abundant in the juice of the common sorrel (Rumex acetosa), of the wood sorrel (Oxalis acetosella), and in the leaf stalks of the common rhubarb. It is principally used for removing ink spots and iron stains from cloth.

Ammonia, Spirits of Hartshorn, or Volatile Alkali-in its uncombined form, an elastic gaseous body, having a very pungent and suffocating odour, destroys animal life, converts the yellow of turmeric paper to a brown, which, from the volatility of the alkali, is again restored by a gentle heat to its original colour. This gas is rapidly absorbed by water, which takes into solution 727 times its volume at 59° Fahr., and 1050 times its volume at 32° Fahr., forming the liquor ammonia of commerce.

Tungstate of Ammonia.-It is used for rendering linen, cotton, and other fabrics non-combustible.

All the salts of ammonia are characterised by the following properties; viz. they are volatile at most at a low red heat; the fixed alkalies and alkaline earths decompose them, uniting with the acid and liberating the ammonia, which may be recognised by its odour and by its alkaline reaction on vegetable colours.

Ammonia is always formed when organic matters containing nitrogen are submitted to destructive distillation; a considerable quantity is formed during the distillation of bones in the preparation of Dippel's oil.

The salts of ammonia are valuable as ingredients in manures, but their chief use is in the production of ammonia alum, which is a double sulphate of ammonia and alumina.

Ammonia, being a highly elastic gas, has been used in place of steam or compressed air to give motion to portable machinery; the compressed gas not only gives motion to the piston by virtue of its elastic force, but after passing the cylinder, may be absorbed by water, thus causing a partial vacuum, and assisting the piston on its return stroke. Owing to these properties it may also be used as a refrigerator, and water frozen by it. To effect this, two strong closed metallic vessels are connected by a pipe. One of these is partly filled with a strong solution of ammonia in water, the other is empty. If now heat be applied to the former, while the latter is kept cool, the ammonia is driven from the water which dissolved it and compressed in the cooler vessel. On the removal of the heat the ammonia returns, to be with great rapidity dissolved in the water again, and in so doing causes a sudden evaporation in the other vessel, and so great an absorption of heat as to freeze a vessel of water in which it may be immersed.

Chloride of Ammonium or Sal Ammoniac.-So called from the circumstance of its first having been procured near the temple of Jupiter Ammon in Libya, from the soot produced by burning camels dung (there used as fuel). It is now, however, prepared in this country from the ammoniacal liquor of the gas-works, by saturating it with muriatic acid, evaporating and crystallising; or by distilling the liquor, and conducting the distillate into muriatic acid. The crystals are purified by sublimation. Sublimed chloride of ammonium forms semi-transparent fibrous masses, very soluble in water, with great reduction of Lithia.-Until very lately supposed to exist temperature; hence it is a common ingredient only in four minerals, but, by the aid of spectrum in freezing mixtures. Used in soldering and galva-analysis, it is now proved to be very extensively disnising iron, with iron filings as cement for iron, &c. | tributed in nature in small quantities. It is found

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