The last described process of making cokes, is now being superseded in many places, particularly in the neighbourhood of Sheffield, by the employment of kilns made of bricks, of a hemispherical form, about ten feet diameter at the base, and about two feet at the top, where a circular opening is left for the introduction of the coal. The manner of working these ovens is thus described by Mr. Parker: - "When these ovens are once heated, the work goes on night and day without interruption, and without any further expense of fuel. It is conducted thus: small refuse coal is thrown in at the circular opening at the top, sufficient to fill the oven up to the springing of the arch; it is then levelled with an iron rake, and the doorway on the side built up with loose bricks. The heat acquired by the oven in the former operation is always sufficient of itself to light up the new charge, the combustion of which is accelerated by the atmospheric air that rushes in through the joints of the loose bricks in the doorway.

In two or three hours the combustion gets to such a height, that they find it necessary to check the influx of the air; the doorway is therefore now plastered up with a mixture of wet soil and sand, except the top row of bricks, which is left unplastered all night.

Next morning, when the charge has been in twenty-four hours, this is completely closed also, but the chimney remains open till the flame is gone, which is generally quite off in twelve hours more. A few loose stones are then laid over the aperture, and closely covered up with a thick bed of sand or earth. All connexion with the atmosphere is now cut off, and in this situation the whole remains for twelve hours to complete the operation. The doorway is then opened, and the cokes are raked into iron wheel barrows, to be carted away. The whole operation takes up forty-eight hours, and as soon as the cokes are removed, the ovens are again filled with coal for another burning. About two tons of coals are put in for each charge, and the cokes produced are ponderous, extremely bard, of a light grey colour, and shine with metallic lustre; they acquire in the furnaces an intense heat, and will sustain a great burthen of iron-stone and other materials." When coke is required to be more of the nature of charcoal, the process is conducted in a different manner. The small coal is thrown into a large receptacle, similar to a baker's oven, previously brought to a red heat.

Here the door is constantly open, and the heat of the oven is sufficient to dissipate all the bitumen of the coals, the disengagement of which is promoted by frequently Stirling it with a long rake. The coke from the ovens, though made from the same kind of coal, is very different from that produced by the former operation, this being intensely black, very porous, and as light as pumice stone. Under the article Lime-Burning, a drawing and description of a patent oven for making coke is given, in which the latter operation is made subservient to the first. The mechanical arrangement and process therein exhibited, maybe advantageously applied to the roasting of ores instead of lime, and the coke required for the smelting furnace might be made at the same time. As we have extended our observations on the making of coke from pit coal to a length which some of our readers may probably consider to be unsuited to its real importance, we would observe, in the language of Dr. Colquhoun, that this substance "has been the means of advancing the manufacture itself in this country, to an extent which is unparalleled in the history of any other country or nation.

It has now been ascertained, by long experience, that there is no other fuel which is so well fitted at once to supply the heat of the furnace, and, at the same time, to endure the powerful blast which is incessantly forced upon it. It may now be said to be essential to our iron manufacture, which would, indeed, be almost annihilated were the supply of it withdrawn." Without it we should be compelled to lay under wood immense tracts of what are now fertile corn fields, in order to supply, at an enormous expense, a much more imperfect fuel for the furnace. But the treasure of it seems to be inexhaustible, ana not less so the metal for which it is required, as will be seen upon reference to the article Coal, wherein we have given a section of Bradley mine, and the arrangement of the numerous distinct strata cut through to arrive at the coal amongst which there occurs from thirty to forty feet thickness of iron-stone before the principal bed of coal is arrived at.