| 1. | First stage of active creep. |
| 2. | Second do. |
| 3. | Third do. |
| 4. | Fourth do. |
| 5. | The metal ridge closed, and the creep beginning to settle. |
| 6. | The creep settled, the metal ridges being closely compressed, and supporting the roof. |
In the “Report from the select committee of the House of Lords, appointed to take into consideration the state of the coal trade in the United Kingdom,” printed in June, 1829, under the head of Mr. Buddle’s evidence we have an excellent description of the nature and progress of creeps, which we have adverted to in the preceding account. The annexed [fig. 869.] exhibits the creep in all its progressive stages, from its commencement until it has completely closed all the workings, and crushed the pillars of coal. The section of the figures supposes us standing on the level of the different galleries which are opened in the seam. The black is the coal pillars between each gallery; when these are weakened too much, or, in other words, when their bases become too narrow for the pavement below, by the pressure of the incumbent stratification they sink down into the pavement, and the first appearance is a little curvature in the bottom of each gallery: that is the first symptom obvious to sight; but it may generally be heard before it is seen. The next stage is when the pavement begins to open with a crack longitudinally. The next stage is when that crack is completed, and it assumes the shape of a metal ridge. The next is when the metal ridge reaches the roof. The next stage is when the peak of the metal ridge becomes flattened by pressure, and forced into a horizontal direction, and becomes quite close; just at this moment the coal pillars begin to sustain part of the pressure. The next is when the coal pillars take part of the pressure. The last stage is when it is dead and settled; that is, when the metal or factitious ridge, formed by the sinking of the pillar into the pavement, bears, in common with the pillars of coal on each side, the full pressure, and the coal becomes crushed or cracked, and can be no longer worked, except by a very expensive and dangerous process. [Fig. 869.]
The quantity of coals, cinders, and culm shipped coastways, and exported from the several ports of the United Kingdom in the year 1837, was 8,204,301 tons; in 1836, the quantity was 7,389,272 tons, being an increase of 815,029 tons, or 11·03 per cent. in favour of 1837.
The following Table shows the separate proportions of this quantity supplied by England and Wales, Scotland, and Ireland:—
| 1836. | 1837. | Increase. | ||||
|---|---|---|---|---|---|---|
| Tons. | Tons. | Tons. | ||||
| England and Wales | 6,757,937 | 7,570,254 | 812,317 | or | 12·02 | per cent. |
| Scotland | 624,308 | 626,532 | 2,204 | 0·36 | ||
| Ireland | 7,027 | 7,515 | 488 | 6·94 | ||
| Total | 7,389,272 | 8,204,301 | 815,029 | or | 11·03 | per cent. |
PITCOAL, COKING OF. See also [Charcoal].
[Fig. 870.] represents a schachtofen, or pit-kiln, for coking coals in Germany. a is the lining (chemise), made of fire-bricks; the enclosing walls are built of the same material; b, b, is a cast-iron ring covered with a cast-iron plate c. The floor of the kiln is massive. The coals are introduced, and the coke taken out, through a hole in the side d; during the process it is bricked up, and closed with an iron door. In the surrounding walls are 4 horizontal rows of flues e, e, e, e, which are usually iron pipes; the lowest row is upon a level with the floor of the kiln; and the others are each respectively one foot and a half higher than the preceding. Near the top of the shaft there is an iron pipe f, of from 8 to 10 inches in diameter, which allows the incoercible vapours generated in the coking to escape into the condenser, which consists either of wood or brick chambers. For kindling the coal, a layer of wood is first placed on the bottom of the kiln.
The coking of small coal is performed upon vaulted hearths, somewhat like bakers’ ovens, but with still flatter roofs. Of such kilns, several are placed alongside one another each being an ellipse deviating little from a circle, so that the mouth may project but a small space. The dimensions are such, that from 10 to 12 cubic feet of coal-culm may be spread in a layer 6 inches deep upon the sole of the furnace. The top of the flat arch of fire brick should be covered with a stratum of loam and sand.