REFRACTORIES FOR GASWORKS PURPOSES 221
used for attaching the mouthpiece. The more modem and satisfactory method, however, is to form the last couple of feet from a short length of moulded retort as seen in Fig. 119. This is, as in the ordinary way,
Fig. 119.—Segmental Retobt with Moulded Mouthpieces.
composed of Stourbridge clay, which possesses the advantage that it is not injured by the Condensed alkaline vapour falling back from the ascension. pipe. Silica
material, on the otter hånd, is quickly rechiced to a powder in this way.
Present day vertical retorts are, of course, almost exclusively built up from rebated silica bricks or segments.
THE COST OF RETORTS
At the present time, prices for retorts must be given with caution, as there are obvious indications that the figures are unlikely to remain stationary. At the same time, much depends upon the locality, also the size of the works, the larger gasworks with. big demands naturally being supplied at a lower figure than a smaller' concern requiring an identical article. Taking London delivery as an average instance, however, the following figures may be given :—
Standard specification retorts . . 15s. to 16s. 6rf. per foot run, delivered.
Good quality (not to specification) . 13.s. 6rf. to 14.s. 6rf. „ ,,
5 egmental retorts :
1. All aluminous material . . 16<s. 6rf. to 18s. „ „
2. Silica tops, aluminous base - . 17s. 6<Z. to 19s. 6d. „ „
These prices are all for average sizes. The very large patterns would be slightly more costly, whilst very small sizes would be rather less. Special shapes are, of course, extra.
With regard to the actual laying of segmental retorts, an additional cost (com-pared with. moulded types) of from 2s. 6d. to 3s. per foot should be allowed.
PROTECTION FOR RETORTS
Owing to the expansion of the siliceous material employed in the cross-walls and other portions of the setting, the retorts often. sufier damage from the increased stresses put upon them. A method for overcoming this effect, which. has been employed with some considerable success, is th.at shown in Fig. 120. The idea, as will be seen from the sketch, consists in placing a shuttering of wooden strips com-pletely around the sides and top of the retort, the strips being built into each cross-wall as it goes up. As the temperature of the setting is gradually raised, the wood chars, and finally burns completely away when the working heats are obtained, thus providing a small space for expansion, and preventing undue pressure on the retort.