the assay of metals, to discover the presence of iron; dissolved in nitric acid, it also forms the aqua regia of commerce.

Native ammonia is found in the vicinity of volcanoes, in some of the mountains of Tartary and Thibet, and in some of the Tuscan lakes. It has also been detected by Dr. Marcet in seawater. On pit coal it may also be sometimes seen in a yellowish white powder.

Why is old decomposed dung comparatively useless as manure?

Because, as soon as dung begins to decompose, it throws off its volatile parts, which are the most valuable and most efficient.

Why is soot a powerful manure?

Because it possesses ammoniacal salt, empyreumatic oil, and charcoal, which is capable of being rendered soluble by the action of oxygen, or pure vital air.

Why are the stem and leaves of the beet-root valuable? Because, when dried and burned, they yield ashes so rich in alkali, that it melts easily by heat, and surpasses many of the common varieties of potassa.

SULPHUR.

Why are common pyrites roasted to obtain sulphur? Because, the fumes being received into a long chamber of brickwork, the sulphur is gradually deposited; it is then purified by fusion, and cast into sticks.

Why will a roll of sulphur, when suddenly seized in a warm hand, crackle, and sometimes fall in pieces?

Because the action of heat is unequal, the sulphur conducting it but slowly, and having little power of cohesion.

Sulphur is one of the few elements which occur in nature in their simple form. It is a well known mineral substance, found in large quantities in the neighbourhood of volcanoes, and as an article of commerce is chiefly brought from the Mediterranean. The effects

of heat upon sulphur are very curious. It is readily melted and volatilized, and begins to evaporate at 170°, and to fuse at 105°. At 220° it becomes completely fluid; between 226° and 228° it begins to crystallize; between 230° and 284° it is as liquid as clear varnish, and of an amber colour; at about 320° it begins to thicken, and acquire a red colour, and on increasing the heat, it becomes so thick that it will not pour. Between 428 and 572°, the colour is a red brown; from 572° to the boiling point it becomes thinner, but never so fluid as at 248°; the deep red brown colour continues till it boils. It sublimes (this term is used to denote the evaporation of a solid) at 600°, and condenses into the form of a powder, or, as it is termed, of flowers. When poured into water, in complete fusion, it becomes of the consistency of wax, and of a red colour; it may then be used for taking impressions from engraved stones, and hardens upon cooling. In a French Journal we read, "though it is well known that sulphur which has been recently fused does not immediately recover its former properties, no one suspected that it required whole months, and even a longer period, fully to restore it."

Why is sublimed sulphur, for delicate purposes, washed with hot water?

Because it is always slightly sour. The purity of sulphur may be estimated by gradually heating it upon a piece of platinum leaf; if free from earthy impurities, it should totally evaporate. It should also be perfectly soluble in boiling oil of turpentine.

Why is sulphuretted hydrogen of easy production? Because sulphur, in its ordinary state, always contains hydrogen, which it gives off during the action of various bodies for which it has a powerful attraction. Berzelius, by heating sulphur with oxide of lead, remarked the formation of water, but in such small and indefinite quantities, as induced him to adopt the gen

erally received opinion, that the presence of hydrogen is accidental, and that it is not an element of sulphur. This illustration is quoted by Mr. Brande in his valuable Manual. It is indeed simple and beautiful, since the reader need not be reminded of the ready production of oxygen from heating oxide of lead, and the formation of water by the combination of oxygen and hydrogen.

Of all the gases, sulphuretted hydrogen is perhaps the most deleterious to animal life. A green-finch, plunged into air which contains only 1-1500th of its volune, perishes instantly. A dog of middle size is destroyed in air that contains 1-800th; and a horse would fall a victim to an atmosphere containing 1-250th. Dr. Chaussier proves, that to kill an animal, it is sufficient to make the sulphuretted hydrogen gas act on the surface of its body, when it is absorbed by the inhalants.

Why is sulphur used in bleaching?

Because, when burned, its fumes combine with the oxygen of the atmosphere, and thus produce sulphurous acid gas. This first reddens blue colours and then destroys them: it is much used in whitening silk and straw-work. According to Pliny, it was used in his time for bleaching wool. Upon some colouring matters, however, as that of cochineal, sulphurous acid has scarcely any action; and when it does destroy colour, the original tint may often be recovered by a stronger acid. A red rose, for instance, is bleached by dipping into a solution of sulphurous acid; but the colour is restored by immersion in diluted sulphuric acid. Why has a gun a peculiar smell after firing?

Because of the sulphuret of potash formed by the exploded sulphur and nitre of the gunpowder.

SULPHURIC ACID.

Why is water necessary, with sulphurous acid oxygen, to produce sulphuric acid?

Because the acid gradually unites with a further proportion of oxygen, and the compound is taken up by the water. When sulphur is burned in dry oxygen gas, there is no change of volume. Again, on the mixture or dilution of sulphuric acid, great heat is given out by the further admixture of oxygen. Four parts

of acid and one of water, produce, when suddenly mixed, a temperature=300°. According to Dr. Ure, the greatest heat is evolved by mixing 73 of acid with 27 of water.

Sulphuric acid is also obtained without nitre, by a patented process invented by Mr. Hill. "Coarsely powdered iron pyrites are submitted to a red heat, in cylinders communicating with a leaden chamber containing water; part of the sulphur, as it burns out of the pyrites, appears at once to pass into the state of sulphuric acid."—Brande.

Native sulphuric acid is not uncommon. In 1829, M. Egidi, druggist of Ascoli, witnessed in a spacious cavern a violent disengagement of sulphuric hydrogen, which, in contact with atmospheric air, became gradually decomposed, and produced water and sulphur; the latter deposited on the sides of the cavern, and principally formed sulphates of lime crystallized; and lastly, sulphuric acid, running down the sides of the cavern. Professor Eaton describes the natural occurrence of sulphuric acid in large quantities, both in a diluted and a concentrated state, in the town of Byron, ten miles south of the Erie canal. The place has been known in the vicinity, for seventeen years, by the name of the sour springs, and consists of a hillock 230 feet long and 100 broad, of an ash-coloured alluvion, containing an immense quantity of exceedingly minute grains of iron pyrites; it is mostly covered with a coat of charred vegetable matter four or five inches thick, and black as charcoal; the same kind of matter extends on all sides, from the base of the hillock over the plain. Its charred state is caused wholly by the

sulphuric acid. In wet spring seasons, plants flowered on this hillock sooner than on the adjoining grounds; but as soon as the spring rains began to decline, then the vegetables withered away, and appeared as if scorched. About two miles east of this place is another sulphuric acid spring, still more remarkable in one respect. The quantity of water from this spring is in sufficient quantity to turn a light grist-mill; and yet there is so much sulphuric acid present in it, that the stream will constantly redden violets, and its water coagulate milk. It is supposed that the sulphuric acid is produced in some way by the decomposition of the pyrites in the soil.-Silliman.

Cases of poisoning by sulphuric acid are not unfrequent; the best antidotes are copious draughts of chalk and water, and of carbonate of magnesia and water.— Orfila.

Why is sulphuric acid also called oil of vitriol?

Because it was formerly obtained by the distillation of green vitriol. It is now procured by burning a mixture of about 8 parts of sulphur, and of nitre, in close leaden chambers containing water, by which the fumes produced are absorbed, and by evaporation the acid is procured in a more concentrated state.—Parkes. Why should sulphuric acid always be kept closely stopped?

Because it rapidly absorbs water from the atmosphere; so that, in moist weather, 3 parts by weight increase to 4 in 24 hours.

Why is sulphuric acid important in dyeing blue? Because it instantly dissolves indigo, which, at first deep purple, becomes blue by exposure to air, or by dilution.

PHOSPHORUS.

Why is phosphorus obtainable from bone earth? Because of the phosphate of lime in bones; which,