[30] An account of the original construction of the rotary retort may be seen in the Repository of Arts, No. CLXXVI, 1816, page I. and also in the Journal of Science, Vol. II. page 133.
The following account will render the construction of this retort sufficiently obvious:
Description of the Horizontal Rotary Retorts at the Royal Mint.[31]
[31] The retorts lately erected at the Gas Works, at Birmingham, Chester, Bristol, &c. are similar to those at the mint.
The horizontal rotary Retorts at the Royal Mint, are hollow cylinders, eight feet six inches in diameter and 15 inches high, arched a little at the top. They are made of wrought-iron plates, half an inch thick, rivetted together in the manner of a steam-engine boiler; A, A, A, fig. 2, [plate III.] exhibits a perpendicular section of the rotary retort. In fig. 1, [plate II.] the retort is seen fixed in the brick-work; a, fig. 1, [plate II.] shews the mouth of the retort, through which the coals are introduced, and from whence the coke is withdrawn. It is also shown in perspective at B, B, B. fig. 2. [plate VII.] The mouth is closed with a cast-iron door fitted on air-tight by grinding.
The door is connected at its upper and lower extremities, with a frame and adjusting rod, see B, B, fig. 1, [plate II.], and also [plate VII.], by means of which it may readily be slided down below the mouth of the retort, when the coals are to be introduced, or coke is to be withdrawn. To the upper extremity of the rod B, fig. 1, [plate II.], is fixed a lever, loaded with a counterpoise weight C, to balance the door, and to render the opening and closing of it easy and expeditious.
The mouth-piece and its door is three feet long, and nine inches wide; it projects nine inches beyond the brick-work or furnace in which the retort is fixed, as may be seen at fig. 1, [plate II.]
The fire-place, which is on the opposite side to that of the mouth of the retort, heats only one-third part of the whole capacity of the retort to that degree which is proper for the complete and rapid decomposition of the coal, while the remaining parts, which are not over the fire-place, and to which the fire flues do not extend, are kept at a lower temperature.
The flues are directed under about one-third of the area of the bottom of the retort, and after having passed over one-third part of the area of the top of the retort, they pass into the chimney. Fig. 1, [plate VI.], exhibits the direction of the flues; A, A, the flues, and the fire-place. The whole retort is guarded from the contact of the fire, which would soon destroy it, by fire-bricks; it notwithstanding speedily receives the full effect of the heat, and retains its temperature when once heated for a long time. Fig. 1, [plate II.], exhibits one of the retorts fixed in its furnace. A perspective view of three retorts may be seen in fig. 2, [plate VII.]
Through the centre of the retort, passes perpendicularly, an iron shaft D, as shown in the section of the retort, fig. 2, [plate III.], and also in fig. 1, [plate II.] The lower extremity of the shaft revolves upon the bottom of the retort, in a cup-shaped cavity, while its upper extremity passes through the roof of the retort, where the latter is made air-tight by means of a pipe E, fig. 1, [plate II.], and E, fig. 2, [plate III.], closed at the top and surrounding the shaft, and hence the shaft must always preserve its centre.