Experiment 10. Into a solution of sulphate of iron, introduce some iron filings; let the whole remain for a few hours; then decant the fluid and add to it prussiate of potash; a white precipitate will be obtained.

Rationale. The iron added to the sulphate, abstracts a portion of oxygen from the oxyd of iron, previously combined with the sulphuric acid, so that when prussiate of potash is mixed with it, a white prussiate of iron is precipitated. Hence iron, at the minimum of oxydizement, forms with prussic acid, a white prussiate.

Experiment 11. Write on paper with a weak solution of sulphate of iron, let it dry and the writing will be invisible. By dipping a feather in a solution of prussiate of potash, and drawing it wet over the letters, the writing will be restored and the letters will be of a bright blue.

In this experiment, prussiate of iron is formed. Hence the formation of a sympathetic ink.

Experiment 12. If paper be written on with an infusion of galls, the characters will not be legible till a solution of sulphate of iron is applied; they then appear black.

Rationale. When sulphate of iron is applied, the gallic acid of the infusion, it is generally considered, unites with the iron into a gallate of iron, and is thus rendered visible.

Experiment 13. If half an ounce of sulphate of iron, one ounce of powdered galls, and a quarter of an ounce of gum arabic be mixed together, the ink powder for forming ink will be prepared; and,

Experiment 14. If sixteen ounces of rain water be added to this powder, writing ink will be formed.

Rationale. Although in a dry state the materials, of which the ink powder is composed, do not act upon each other, yet when water is added, the sulphate of iron and gallic acid of the galls are taken up, and produce gallate of iron. The gum is intended to suspend the precipitate or gallate of iron. For further particulars, see Salts of Iron.

Experiment 15. If to the black liquid, formed by adding infusion of galls to the sulphate of iron, a few

drops of muriatic acid be added, the whole will become limpid; and,

Experiment 16. If to this limpid fluid the addition of a solution of potash be made, the black colour will be restored.

Rationale. The gallate of iron is decomposed by the muriatic acid, and muriate of iron is formed. The addition of potash then unites with the muriatic acid, and the oxyd of iron is set free, which combines with the gallic acid into a gallate of iron. Some caution is necessary in adding the alkali, in order to produce the desired effect.

Experiment 17. If a piece of calico be immersed in a colourless solution of sulphate of iron, and, when dry, washed in a weak solution of carbonate of potash, a permanent colour will be produced, viz. the buff of the calico printers.*

Rationale. The sulphuric acid of the sulphate of iron, combines with the potash, forming sulphate of potash, whilst the carbonic acid of the carbonate of potash passes to the iron, and is fixed on the stuff in the state of carbonate of iron.

Experiment 18. If ether be added to a solution of iron in muriatic acid, the preparation known formerly under the name of Lamotte's gold-drops will be produced.

Experiment 19. If muriate of ammonia be sublimed in contact with iron filings, or its oxyd, the martial flowers of sal ammoniac will be prepared.

Rationale. Part of the muriate is decomposed, muriated iron is formed, which sublimes with the unde composed muriate of ammonia. See Salts of Iron.

Experiment 20. If hydrogen gas, obtained by adding diluted sulphuric acid to iron filings, be suffered. to stand undisturbed, a brown powder will be deposited on the sides of the jar. This powder has been found to be iron.t

Remark. Although hydrogen has never been united to iron in its solid state, yet this first furnishes a proof that they may be combined.

* Parke.

†Thomson, i. 225.

Experiment 21. If equal parts of glacial acid of phosphorus and iron filings, be fused together, a phosphuret of iron will be formed; or,

Experiment 22. If equal parts of the glacial acid of phosphorus and iron filings, mixed with half a part of charcoal powder, be melted in a covered crucible, the same compound will result.

Rationale. In the first experiment part of the iron unites with the oxygen of the phosphoric acid, and the other part combines with the phosphorus into a phosphuret, which sinks to the bottom of the crucible.

In the second experiment the charcoal decomposes the phosphoric acid; carbonic acid is disengaged, and the phosphorus unites with the iron. The phosphuret of iron may also be formed in the following man

ner:

Experiment 23. Heat iron filings red hot in a crucible, drop in phosphorus, and cover the vessel.

Remark. It was this compound, which Bergman took for a new metal, and gave it the name of siderum. Both Bergman and Meyer supposed, that it was this compound, which they then considered a peculiar metal, that gave to that particular kind of iron, known by the name of cold short, the property of being brittle when cold. The subject was afterwards investigated by Klaproth, who proved, that the white powder obtained from cold short iron, contained phosphoric acid and iron. Scheele decomposed this powder, and formed the same conclusions. The siderum of Bergman, however, is composed of phosphorus and iron, the phosphoric acid being deprived of its oxygen during the reduction.

Experiment 24. If two parts of sulphur and one of iron filings be melted together in a crucible, a compound will be formed called sulphuret of iron, which is of a black or very deep gray colour; or,

Experiment 25. If iron be ignited, and in this state applied to a roll of sulphur; both of them will be fused, and the sulphuret will fall down in drops.

Experiment 26. If a mixture of one part of iron lings and three of sulphur, be melted in a glass tube,

at the moment of union a brilliant combustion will

ensue.

Experiment 27. If equal parts of iron filings and flowers of sulphur, worked with water to a paste, be exposed to the air, the mass becomes hot, falls to pieces, and is converted into sulphate of iron.

Rationale. The sulphur unites with the iron into a sulphuret, which decomposes the water in part, and in part absorbs oxygen from the air. The sulphur is therefore acidified, and in union with the iron, forms the sulphate of iron.

Remark. A hundred pounds of iron filings were mixed by Baume, with an equal quantity of sulphur, which was moistened with water, and rammed into an iron pot. After ten hours the mass swelled up and grew warm, aqueous vapours arose, and the mass burst. Ten hours afterwards, the heat, vapours, and odour, greatly increased, and a flame issued forth, lasting only from 2 to 3 minutes. Finally, the mass became red hot, and the burning and heat continued 40 hours longer; but without flame. A similar mixture forms Lemery's volcano, the mass being laid under the ground.

Sulphuret of iron, according to Proust, is composed of 62.5 iron and 37.5 sulphur in the hundred. Iron pyrites are composed of iron and sulphur. If sulphuret of iron be added to sulphuric or muriatic acid, a solution readily ensues, emitting abundance of sulphuretted hydrogen. When heated with nitric acid, much sulphur is separated.

Experiment 28. If iron filings be added to a solution of sulphuret of potash, they will be in part dissolved; and,

Experiment 29. If an acid be poured into this solution, a precipitate of hydrosulphuret of iron will be produced; or,

Experiment 30. If a solution of sulphuret of potash be added to another of iron in any acid, the same compound will be formed; or,

Experiment 31. If a polished plate of iron be immersed into an hepatic water, or water holding sulphu

retted hydrogen gas in solution, it will become blackened. See Hydrosulphurets.

Experiment 32. If iron filings be mixed with sulphuret of copper, and exposed to heat, sulphuret of iron will be formed, and the copper separated. In this way copper may be separated from sulphur.

Experiment 33. If five parts of iron filings be heat' ed to redness in a crucible, and sixteen parts of powdered sulphuret of antimony introduced into it, and the whole exposed to a sudden and strong heat, the sulphur will leave the antimony and pass to the iron. When the mixture is thoroughly fused, a little nitre added will facilitate the separation of the scoriæ from the antimony.

Experiment 34. If one part of iron be melted with two of sulphuret of antimony, a little iron will remain united with the antimony, forming the martial regulus.

Remark. The combination of carbon and iron, forming what is called carburet of iron, plumbago, and black lead, which is found native, appears to be composed of 90 carbon, and 10 iron in the hundred.

Iron, in order to distinguish the different varieties, is known to artists by the names of cast or pig iron, wrought or soft iron, &c.

Cast iron, or pig iron, is the name of the metal when first extracted from its ores; the process made use of has already been noticed. There are several varieties of cast iron, distinguished from its colour and other qualities viz. white cast iron, gray or mottled cast iron, black cast iron, &c. Cast iron melts when heated to about 130° Wedgwood. Its specific gravity is about 7. It is converted into soft or malleable iron by a process called refinement. This is generally accomplished by keeping the iron for a considerable time in a bed of charcoal and ashes, and then forging it repeatedly till it becomes compact and malleable. The process of refinement, however, varies in different countries, according to the nature of the ore and the fuel employed. Mr. Cort's process consists in melting the cast iron in a reverberatory furnace by means of the flame of the combustibles, which is made to play upon its surface