incapable of performing its full measure of duty in the furnace. Thus the increased yield in the oven is considered as being neutralised, by the coke having less value when it reaches the ironworks, than has the produce of the ovens constructed without such flues, and with no external heating of the contents.

Some of our most experienced authorities, who have given the subject much attention, were led to infer that for obtaining hard burnt coke the heat afforded by the combustion of the gases did not suffice, and that the high temperature required must be continued, after the process of distillation was completed. This, according to their opinion, can only be secured by the burning of a portion of the coke itself.

A careful examination of the ovens abroad, and analyses of the gases taken at various stages of the process in the collieries of my own firm, led me to adopt an opposite conclusion; and by a mere change in the way in which the air is admitted, this serious source of waste is in some measure removed.

By the two alterations just described, viz. that of utilizing the heat for steam purposes and a reduction in the waste of coke, it has been estimated that, of the 242,000 calories calculated as disappearing, something like 100,000 may be saved; viz. 56,000 by avoiding a part of the waste in the coke itself, and 44,000 calories in the generation of steam.

Among the more elaborate systems of coke making, that known as the Knab process, from the name of the inventor, is deserving of notice. In every case where air is allowed access to the gases immediately on leaving the coal, they are speedily converted into watery vapour and carbonic acid-the hydrogen of the hydro-carbons giving rise to the formation of water, and the carbon to that of carbonic acid. If, instead of this mode of procedure, the distillation is conducted in closed vessels, and the volatile matter is passed through proper condensers, the same products are obtained which accompany the manufacture of illuminating gas, viz., ammoniacal compounds and coal-tar, the latter yielding creosote, asphalte and aniline dyes. The inflammable gas, after being freed from these less volatile substances, is brought back to the oven, where by its combustion in external flues the coal is converted into coke.

In two localities, viz. at South Brancepeth Colliery belonging to my firm, and at Wigan, this system has had an extensive trial in this country; and the result was final abandonment in both cases, mainly owing to the difficulty of upholding the buildings. In France also, the land of its first introduction, there are not above two or three establishments where it is in operation. Nevertheless, it is difficult not to believe that the idea is a very valuable one; for M. Carvés, who has had several years experience in working it, has recently, at his own expense, erected an establishment at a cost of about £20,000, at some iron furnaces near St. Etienne. At the end of a certain term of years he will hand the ovens, etc., over to the furnace owners free of charge, his remuneration consisting exclusively of a share of the profits reaped in the meantime from the sale of the tar and ammoniacal salts.1

In South Wales and Staffordshire, coal is often coked in the open air, by piling blocks of coal round a low central chimney. This however, is a plan which cannot be recommended for adoption, the waste of coal, especially in high winds, being enormous.

PRELIMINARY TREATMENT OF WOOD.

When the forest, instead of the mine, is the source of the fuel, previous charring is almost invariably practised. The exception is where the wood is highly dried; but in this state it is a small proportion only which can be employed in iron smelting. The volatile matter, consisting of gas and a large quantity of water, which is capable of expulsion from wood by heat, is so great, that about 25 per cent. of the weight of timber employed represents a common yield in charcoal.

In the woods of the United States, a square acre of forest affords about 20 to 40 cords of timber, each measuring 128 cubic feet as it is stacked. This forest, if allowed to grow again, would not be fit for cutting for thirty or forty years. Very frequently, however, the lands used in the Western World for obtaining charcoal remain cleared for agricultural purposes. The actual weight of charcoal afforded by an acre of ground varies from 7 to 14 tons. This is evidently too small a quantity to

I understand that Messrs. Pease are at present erecting a coking work, in the County of Durham, at which they propose collecting the products of distillation in the manner described.

permit of any permanent erections for charring, even if the wood-lands were intended to be exclusively devoted to supplying the ironworks with fuel. The reason is obvious. The conveyance of 100 tons of timber, giving at the outside 25 tons of charcoal, would entail so much expense, owing to the distances apart of the trees to be felled, that any particular building would speedily have to be abandoned from unsuitability of position. The consequence is that the wood is almost all charred in heaps formed on the ground; and from the cause already mentioned, a blast furnace so speedily consumes the trees in its immediate vicinity, that the expense of conveying the charcoal to the works becomes an important item in the cost of the fuel.

It is true that near Marquette, on the shores of Lake Superior, the charcoal is made in large close kilns; but this is done from necessity and not from choice, and is owing to the length and severity of the winters, any saving in labour or gain in produce being more than counterbalanced by the additional charge incurred on the carriage of the volatile constituents of the wood.

From numerous enquiries made during visits to the American forests, I have estimated the cost of a ton of charcoal to be as follows:

The price of transport varies according to distance; sometimes it is a mere trifle, but 5s. or 6s. per ton is a common charge for this item, and occasionally the carriage comes to as much money as the cost of the charcoal itself.

In Austria the cost of a ton of charcoal delivered at the furnaces was given me as running from 30s. to 56s. per ton. In Sweden the iron master who owns the forest lands obtains his fuel for about 20s.; but inclusive of the value of the wood 30s. to 35s. will represent more nearly the price of a ton of charcoal in that country.

The price paid for charcoal, under the conditions of production just described, will vary greatly according to the state of the iron trade. With low selling rates of his produce, the smelter who is depen

dent on charcoal brought from long distances, and often over very bad roads, will curtail his make of pig; and so discontinue the use of fuel, one-half of the cost of which may be incurred in transporting it from the forest to the furnace.

These prices of charcoal have been quoted with a view to show under what disadvantages, in point of cost, iron is manufactured, when using this description of fuel. In the coal-fields of Great Britain, coke is usually delivered at the furnaces at about 12s. per ton, or at about one-half the sum paid for charcoal in America. Practically the manufacture of charcoal iron in the United Kingdom may be regarded as a thing of the past. Messrs. Harrison Ainslie and Co. still smelt about 1,800 tons of this article per annum, which is chiefly used for making malleable iron castings, that is, castings which are rendered malleable by a prolonged heating in contact with an oxidizing substance like peroxide of manganese. I am informed that at their furnaces charcoal costs 45s. to 75s. per ton. For use in tin works charcoal, down to a recent period, commanded 40s. to 50s. per ton, but here again Bessemer steel bars bid fair to drive iron out of the market, so that charcoal fires are fast disappearing.

PRELIMINARY TREATMENT OF THE ORES OF IRON.

The ores of iron, as they are delivered to the blast furnace, may be divided under three heads :

1.-Simple oxides, viz. magnetic oxide (Fe, O.) and peroxide

(Fe, 0), which contain no combined water, but often a considerable quantity of included moisture, as in the case of ores from the mines of Lancashire.

2.-Peroxide of iron containing combined water, as in brown hematite.

3.-Ores in which the metal exists as a carbonate of the protoxide (Fe O CO2).

The first two are occasionally found nearly pure; in most cases however they contain from 10 to 15 per cent. or more of earthy matter. The carbonate, when occurring as spathose ore, is also sometimes almost pure; but in the usual run of clay ironstone, in which the metal is likewise combined with carbonic acid, the foreign matter exists in such

quantity as to reduce the yield to from 28 per cent. to 40 per cent. Occasionally clay stone contains even more than 40 per cent. of metal; but 30 per cent. represents the ordinary produce of this variety of the mineral, which is by far the most plentiful of all.

Practically it may be said, that for all ores in which the iron exists in the form of carbonate, recourse is had to calcination, before their delivery to the blast furnace. The change effected by the operation is the expulsion of combined water and of moisture, while the metal is peroxidized, and a portion of any sulphur present is driven off.

In some cases, as in Sweden and elsewhere, the ores of the oxide class are occasionally calcined before they are submitted to the action of the blast furnace. The mineral is by this treatment more readily reduced, and to some extent the sulphur it may contain is removed.1 As a rule, however, the oxides are smelted as they are raised from the mine, unless it has been necessary to remove foreign matter by any of the usual modes of washing when the same is capable of being so separated.

Clay ironstone is frequently calcined in the open air, in heaps or clamps as they are called. This is a very wasteful method both in fuel and labour; but in the case of Black Band clay stone the quantity of coal associated with the ore is so great, that it would be difficult to calcine it alone in a kiln. This is owing to the liability of the mineral to run together, by the high heat evolved during the process of calcination.

The apparatus used for the operation in question has been greatly improved, in late years, in the district of Cleveland. The kilns are as lofty as the blast furnaces formerly were, by which means the fuel consumed is reduced to about 34 per cent. of the mineral employed; and they are so constructed that they are self-discharging into the furnace barrows. The credit of these improvements is due to Mr. John Borrie of Middlesbrough, and they seem so complete as to leave little room for further amelioration.

It has been proposed to use a portion of the ironstone uncalcined; and making allowance for the loss of coal which is incurred, even in the well constructed kilns just described, it may be granted that the quantity

By experiment I ascertained that previous calcination greatly facilitated the reduction of an ore by means of carbonic oxide. (See "Chem. Phen. of Iron Smelting.")