with a piece of charcoal. The crucible is then closed, the number of the assay being marked on the inner surface of the cover. This is then fastened down air-tight with some putty.

The iron ore, after these preliminary arrangements, is to be submitted to a reduction process in the furnace, fig. 6, Plate I., which lasts about three-quarters of an hour.

At the extensive iron-works on the Hartz Mountains in the interior of Germany, a very simple apparatus is used instead of the other furnace, of which, on account of its portability, I here give a description. It consists simply of an open cast-iron pot or jar, measuring about a foot across, and one and a half in height, and having a plate of sheet-iron, perforated with many little holes an inch in diameter, instead of u grate. This leaves a vacant space of about two inches below, to receive the ashes. The latter partition has two open

ings; one, the door to take out these cinders—the other, to introduce the end of the bellows. Above the iron plate, on which the crucibles are directly placed, without any brick, a coating of fire-clay, an inch thick, extends to the mouth of the jar.

The latter is furthermore supplied with three or four short legs, and a handle on each side.

In this furnace the process lasts about an hour and a quarter.

In both cases, the button produced contains exactly the same impurities, carbon, earths, acids, or other metals, as pig-iron would, if procured from the same ore, and therefore this assay is only to be used for furnaces. For these it entirely suffices; but to ascertain the true amount of pure iron, the wet analysis should be resorted to, the same as with other ores; and it is for this that I shall give directions in the next chapter how to discover or calculate the real per-centage of the pure metal, or to

assay the pig-iron produced in the process by heat.

It may not be uninteresting to many, who may honour these pages with their perusal, to become acquainted with a method for obtaining chemically pure iron, as given by Karsten in his famous and voluminous works on this metal. It is described in vol. i., pages 167, 168. He says, to procure chemically pure iron, take the best bar-iron of commerce, e. g. Swedish iron in the shape of small wire; cut it up in short pieces, and then mixing it with about a fourth part by weight of oxide of the same metal, melt it in a Hessian crucible. To cover it, use a compound flux, consisting of pure quartz, pure lime, and equally pure carbonate of potash, in proportions capable of furnishing a glass or slag, not flowing too easily, but of rather a tough consistency.

For the manufacture of an oxide of iron, free from all admixtures of foreign metals,

it is best to use small clean wire, oxidizing it by vapours of water.

The button thus produced has a remarkably white colour, a strong metallic lustre, and is more ductile than the best varieties of soft bar-iron. Particularly characteristic, however, is its great specific gravity, amounting to 7.9654, while that of wrought-iron is 7.6 to 7.9, and of castiron only from 7.0 to 7.5. The only impurity this metal may be discovered to possess occurs as slight traces of silicium, and therefore it may be considered to be as pure as it possibly can be made, even by a process conducted only upon the rules and principles of wet analysis, and thus in this shape it is utterly unknown to the mere practical metallurgist or smelter.

XVIII.

Fuchs's Process for Iron Ores and Iron.

THIS method, though remarkable for its simplicity, is a very sure one, not only to ascertain the quantity of iron in an ore, but to acquaint us with the peculiar degree of oxidation in which it exists, and also the amount of each oxide, which it is often not only very interesting, but useful to know. Many ores, particularly the magnetic ones. contain both the peroxide and the protoxide, and the only ones to which this process cannot be applied are those containing arsenious acid, not a very common ingredient.

The process discovered or invented by Fuchs is founded on the fact, that chemically pure muriatic acid, when atmospheric air is excluded, is incapable of dissolving any