tion with sulphur at a gentle heat for several days; then, by a careful evaporation at a moderate temperature, large and regular crystals of hyposulphite of soda, NaO,S2O2, are obtained, which are very soluble in water.

Nitrate of soda, NaO,NO5.—Cubic Nitre occurs native in enormous quantities in Peru, where it forms regular beds to a very great extent. The nitrate of soda, NaO,NO,, is used for making nitric acid, NO5; but it cannot be used for gunpowder, as the salt burns too slowly and absorbs moisture.

The tribasic phosphate of soda, 2NaO,HO,PO, + 24HO, is prepared by precipitating the phosphate of lime with the carbonate of soda.

A second salt, sometimes called the sub-phosphate, has the formula 3NaO,PO5 +24HO. This is obtained by adding caustic soda to the preceding salt.

The tribasic phosphate of soda, and ammonia, and water, Microcosmic Salt, NaO,NH1O,HO,PO5+8HO. This salt is prepared by dissolving six parts of the common phosphate of soda in two of water, when the whole is liquefied. One part of chloride of ammonium, NH Cl, is added; when the chloride of sodium, NaCl, separates, which is removed by the filter; and from the properly concentrated solution, the microcosmic salt crystallises out.

Bibasic, phosphate of soda, 2NaO,PO, + 10HO. Monobasic, phosphate of soda, NaO,PO5.

All the tribasic phosphates give a bright yellow precipitate with nitrate of silver, AgO,NO,; the bibasic and monobasic give white precipitates with the same salt.

Biborate of Soda, Borax, NaO,2BO, + 10HO This salt occurs in the waters of certain lakes in Persia. The impure salt is imported to this country

from the East Indies, under the name of tincal. A great quantity of this salt is now prepared from the native boracic acid, BO,, of Tuscany, where it occurs, uncombined, in the hot springs of that country. Although this is an acid salt, it has an alkaline reaction to test-paper. It is used in the arts for soldering metals; its action consists in rendering the surfaces of the metals to be joined metallic, by dissolving off the oxide. It sometimes enters into the composition of the glaze with which stone-ware is covered. The refined borax is used by the washerwomen of Holland and Belgium, to whiten linen and to soften water. About a handful is mixed with ten gallons of boiling water. The saving of soap is nearly one half, and the borax does not injure the linen.

Common Salt, chloride of sodium, NaCl.-A large quantity of salt is obtained from saline springs; but our chief supply is from the mines of Cheshire. Rock salt is always too impure for use; and if no natural brine-spring exists, one is formed by sinking a shaft into the rock salt, and introducing water. This water, when saturated, is pumped up, and evaporated in large iron pans. As the salt separates, it is removed by means of a wooden scoop, and pressed, while moist, into moulds, and then transferred to the drying stove. When large crystals are required, as for bay salt, the evaporation is conducted very slowly. Common salt generally contains a little chloride of magnesium, MgCl. The iodide of sodium, NaI, and the bromide of sodium, NaBr, are similar to the corresponding potassium compounds.

Tests.

All the soda salts are very soluble in water, except the antimoniate of soda. The presence of soda is

M

generally determined by purely negative evidence, A solution of some salt of seda is prepared, the chloride of sodium, NaCl, or carbonate of soda, NaO,CO2, may be taken, and five test-tubes half filled with the solution. The following reagents must be carefully added in the order given :—

Add the hydrosulphide of ammonium, NH,HS; no precipitate.

Add carbonate of ammonia, NH,O,CO2; no precipi

tate.

The salt is a compound of potassium or sodium. Add tartaric acid; no precipitate.

Add bichloride of platinum; no precipitate. Quick lime, or caustic potash, and gently heated; no odour of ammonia.

Evaporate the solution to dryness, and observe the colour it gives to the outer flame of a blowpipe. A bright yellow will indicate the presence of soda.

AMMONIUM.

Symbol, NH,; Equivalent, 18.

In connection with potassium and sodium, ammonium may be conveniently studied.

Ammonia, NHO, is the oxide of a hypothetical body, called ammonium. The salts of ammonia correspond exactly with those of potash and soda. All attempts to isolate ammonium have failed, from its tendency to separate into ammonia, NH,, and hydrogen. Ammonium plays the part of a metal in the composition of salts; it is capable of replacing sodium and potassium. The sal-ammoniacum of the Romans

was the hydrochlorate or muriate of ammonia, and was obtained as a natural produce from a district in Libya. It was called by the alchemists spirits of hartshorn, because it was obtained by the distillation of deers' horns, in close vessels. It is sometimes called the volatile alkali.

Although ammonium has never been isolated, it is possible that it is not behind potassium and sodium in metallic lustre, and the ordinary physical characters of a metal.

If a small quantity of mercury be heated in a testtube with a grain or two of potassium or sodium, and a gentle heat applied, violent combination ensues, attended with the production of light and heat. When cold, the fluid amalgam is put into a saucer, and covered with a strong solution of the hydrochlorate of ammonia. The mercury increases enormously in volume, and a pasty ammoniacal amalgam is formed. Left to itself, it quickly decomposes into mercury, ammonia, and water.

The great resemblance the ammoniacal salts bear to those of potash and soda, is the chief argument in favour of the existence of ammonium.

In the manufacture of coal gas, much ammonia is formed by the combination of the nitrogen and hydrogen of the coal. In the manufacture of bone charcoal ammonia is also produced; but in both cases it is very impure.

If a sal-ammoniac be reduced to powder, mixed with quick-lime, and heated in a retort, gaseous ammonia is abundantly evolved; and as water dissolves about 500 volumes of the gas, it must be collected over mercury, or by displacement. The vessel in which the gas is collected must be held above the orifice from which it is issuing, the same as if it were

hydrogen. The following decomposition takes place:

NH,HC1 + CaO = NH, + CaCl + HỌ.

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Ammonia compounds are now largely manufactured from gas liquor, and the condensed products obtained from the distillation of bones and other animal refuse, as mentioned under bone charcoal: It was formerly obtained in Egypt from the soot of camel's dung.

The alkaline action of ammonia may be tried with turmeric, litmus paper, or purple cabbage water.

When ammonia comes in contact with one of the volatile acids, dense white fumes are formed. A test tube rinsed out with hydrochloric acid, HCl, and held over a vessel from which ammonia is issuing, white fumes and solid crystals of sal-ammoniac are formed by the union of the ammonia with the hydrochloric acid, HCl.

If gaseous ammonia, or ammonia water, be added to a solution of sulphate of copper, a splendid azure blue compound is formed. This colour is formed by a bluish precipitate, which is redissolved by excess of ammonia, and the blue colour produced afterwards.

Ammonia, when uncombined, may be readily recognised by any of the characters I have above described. Salts of ammonia, Sal-ammoniac, NH,Cl, is prepared from gas or bone liquor. The solution is treated with a slight excess of hydrochloric acid, HCl, by which the ammonia is neutralised, and the carbonate of ammonia, NH,O,CO2, and sulphide of ammonium, NHS, are decomposed, with evolution of carbonic acid, CO2, and sulphuretted hydrogen, HS. The liquid is evaporated to dryness, and the salt carefully heated to expel the tarry matter with which it is associated. It is then purified by sublimation in iron