hence, in the reduction of ores containing any of these, the addition of one or other of these earths makes à proper flux.

The metal obtained at first is not pure, but contains carbon, &c. In this state it is called smelted, pig, or cast iron. According to the nature and proportion of the foreign matter, the iron appears either light gray, dark gray, blue, or black.

There is one kind of forged iron, which, when cold, possesses ductility; but when heated is extremely brittle. This is called hot short iron. Another variety of forged iron, whose characters are opposite, is called the cold short iron. It is ductile while hot, but when cold is extremely brittle. The cause of that property of cold short iron, depends on the presence of a substance termed siderite, which is a compound of phosphoric acid and iron. On the contrary, that of hot short iron, to the presence of arsenic or sulphur; but the real cause is not known

In order to ascertain the quantity of iron in an ore, Rinman has proposed the following method: Take its specific gravity, and state it in integral numbers, then divide it by 80..

An ore, for instance, whose specific gravity was

3893

31.893 gave

80

48.6, and contained on trial 50 per

cent. of iron. The error was only 1.5 per cent. Ores, whose specific gravity are less than 3.6 should be divided by 150; a small difference, however, will exist. Iron may always be detected by adding to a solution supposed to contain it, either tincture of galls, prussiate of potash, or succinate of ammonia. The first will produce a black, the second a blue, and the third a brown precipitate.

For the analysis of the different ores of iron, see Klaproth's Essays, Kirwan's Mineralogy, and Accum's Analysis.

Iron is one of the most useful metals. It was known to the nations of the east at a very early period. Moses, who was born about 1635 years before Christ, gives ample proof of the knowledge, which the Egyptians a?

Phoenicians had of this metal. Moses not only tells us, in his writings, that furnaces were constructed for the working of iron, but also, that the metal itself was made use of in the manufacture of swords, knives, axes, and tools for cutting stone.* Iron must have been known, in all probability, long before the days of Moses, as Hesiod (quoted by Pliny, lib. vii. c. 57.) observes, that the knowledge of iron was brought over from Phrygia to Greece by the Dactyli. This person settled in Crete during the reign of Minos I, about 1431 years before Christ. We find also, that 200 years after, iron was held in such high estimation, that during the Trojan war Achilles proposed a ball of it as one of his prizes, during the games which he celebrated in honor of Patroclus.

The specific gravity of iron varies from 7.6 to 7.8. It is of a bluish white colour. It is attracted by the load stone, and is itself the substance which constitutes the load stone. It is very malleable, and its mallea bility increases in proportion as the temperature is increased. It is extremely ductile. It possesses considerable tenacity. An iron wire, for instance, 0.378-of an inch in diameter will support a weight of 549.25lbs. avoirdupois, without breaking. At 158° Wedgwood it melts. When broken it appears to be composed of a number of fibres or strings bundled together.

Experiment 2. If iron be exposed to the air, its surface becomes tarnished, and is gradually converted into rust.

Rationale. As iron is one of the metals that is oxydized by the atmosphere, in this experiment it unites" with oxygen, and becomes converted into rust or oxyd.

Experiment 3. If iron filings be moistened with water, and exposed to the atmosphere, they are rapidly converted into rust, which, when ground into an impalpable powder, and made into conical lumps, forms the rubigo ferri or rust of iron of the Dispen

satories.

* See the books of Deuteronomy and Leviticus

Rationale. Iron, by exposure at the same time to air and moisture, is very quickly oxydized. The oxyd thus formed, is said to absorb carbonic acid; hence it has been called carbonate of iron. The proportion of carbonic acid, however, is small. See Salts of Iron.

Experiment 4. If iron filings be introduced into water, not under the temperature of 70°, they are gradually converted into a black powder, and hydrogen gas is emitted ;* or,

Experiment 5. If iron filings be put into a retort containing water, the beak of which is to be plunged into a vessel of water, and the heat of a lamp applied, so that the water may be made to boil, hydrogen gas will come over; or,

Experiment 6. If the steam of water be made to pass through a red hot iron tube, he same product will be obtained. See Hydrogen Gas.

Rationale. In all these experiments water is decomposed; its oxygen unites with the metal, and its hydrogen is disengaged in the form of gas.

Experiment 7. If iron wire, in a white heat, be immersed in a jar of oxygen gas, vivid combustion will ensue; and the metal will be converted into an oxyd. See Oxygen Gas.

Remark. Iron, by uniting with oxygen, is converted into oxyds of different colours. There are two oxyds sufficiently characterized, namely, the black and red oxyd; but Thenard is of opinion, that there are three oxyds, viz. the white, green, and red. The green oxyd of this chemist is supposed by Darso, to owe its colour to the presence of hydrogen, and that the white oxyd is a sub-salt, having always a portion of acid in its composition. Mr. Chenevix, in his paper on Arseniate of Copper, has asserted, that iron is capable of furnishing four distinct oxyds. The first oxyd is white, the

* Thomson, i. 218. Bergman Opusc iii, 95. Scheele on Fire, i. 180,

Thomson, i. 219,

ΤΟΥ

second green, the third black, and the fourth red; but in confirmation of this opinion he does not appear to have adduced any particular experiments. In combination with alumina, clay, &c. iron, in the state of oxyd constitutes with the first the potter's clay, and with the second, some of the ores of iron. In the hematite, the iron is oxydized, forming a calciform iron ore. If lime water be added to a water holding iron in solution as in the aerated chalybeate waters, the iron will be precipitated in the form of a brown oxyd or ochre. Besides giving colour to a great variety of natural substances, as before stated, its oxyd communicates it to the cornelion, the oriental ruby, the garnet, and other precious stones. With different proportions of oxygen it imparts other colours, as the blue to the lapis lazuli, and the yellow to the topaz.

The black oxyd of iron may be obtained in the manner before stated, namely, by wetting iron filings with water at the temperature of 70°. This preparation was known by the name of Martial ethiops. When steam is made to pass through an iron tube, the metal is also converted into the black oxyd; and when iron is burnt in oxygen gas, an oxyd is obtained, which answers to the characters of the black.

If sulphate of iron be decomposed by adding potash, a green powder will precipitate, which, when collected, washed, and dried quickly in close vessels, forms the black oxyd, or martial ethiops. According to Lavoisier and Proust, this oxyd is always composed of 73 parts of iron, and 27 of oxygen. This oxyd is attracted by the magnet. The per oxyd of iron, in which the metal is oxydized to the maximum, may be formed by exposing iron filings, red hot, in an open vessel to the atmosphere, and agitating them till they are converted into a dark red powder. This oxyd is the same as the saffron of mars of the older dispensatories. The common rust, before noticed, is said to be composed of this oxyd and carbonic acid. The same preparation may be formed by exposing a diluted solution of iron in sulphuric acid to the atmosphere,

and then decomposing it by the addition of an alkali; the oxyd being precipitated.

The per oxyd, according to Proust, contains 48 per cent. of oxygen.

When the per oxyd is heated with its own weight of iron filings, it is converted into the black oxyd. It is also converted into the black oxyd by sulphuretted hydrogen gas and many other substances.

Iron is attracted by most acids, with which it forms salts. See Salts of Iron.

Experiment 8. If sulphate of iron be distilled in an earthen retort, a brown coloured matter will remain, and the greater part of the sulphuric acid will pass over.

Rationale. Heat decomposes the sulphate; sulphuric acid distils, and the iron is left in the retort partly in the state of oxyd, and partly combined with a portion of the acid, in the form of sub-sulphate of iron. It was from the distillation of vitriol, to obtain the acid, that the term oil of vitriol took its rise.

Remark. After the distillation of sulphate of iron, commonly called green vitriol, or copperas, the residue has been called colcothar: if this be well lixiviated, it forms the pigment, sold under the name of English brown-red.

The red oxyd of iron of the Edinburgh Dispensatory, is formed by exposing the sulphate to the action of a strong heat.

Experiment 9. If sulphate of iron be dissolved in water, and prussiate of potash added; a blue precipifate will be obtained.

Rationale. The sulphuric acid of the sulphate of iron unites with the potash, whilst the prussic acid of the prussiate of potash, combines with the oxyd of iron, thus separated in the form of a blue precipitate, prussiate of iron, or prussian blue. The preparation of prussian blue, particularly, will be noticed hereafter.

Remark. It is with the per oxyd of iron, that a blue colour is formed with prussiate of potash; with the prot-oxyd, on the contrary, a white precipitate is produced; as,