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tudinally, the grade being arranged, according to the length of the pit, so as to drain towardone end of the pit, or from each end toward the centre, or from the centre toward the ends,or toward several points. The transverse dishing of the paving is usually in the form of ageneral depression, about 2 in. deep, from the sides toward the centre of the pit. Anothermethod is to make the bottom straight transversely with a pitch toward one of the side walls,forming a gutter along the side wall; or the paving is built highest at the centre of the pitand pitches down toward each side wall, forming a gutter along each side wall. The dishingof the paving toward the side walls has the advantage of keeping the centre of the pit dry,but it has the objectionable feature of throwing the water against the side walls. The systemof making the gutter at the centre of the pit is to be recommended, provided the dishing andcurvature are not made so heavy as to impede shovelling. The longitudinal gradient of thepaving must be sufficient to secure proper drainage lengthwise of the pit, and should be notless than I ft. in lOO ft. for brick pavement and more for rough stone paving. Large andwell-designed sink-holes or catch-basins should be built either inside or outside of the pit,preferably the latter, as they can then be larger, and covered up in such a way as to be read-ily opened and cleaned out. Iron gratings at all drain-holes are essential so as to prevent, sofar as possible, dirt and ashes carried along by the water from clogging up the drains. Thedrain leading from the catch-basin away from the pit should be large, especially where a goodfall is not obtainable. It can either be an open ditch, a box culvert, a brick sewer, or a pipedrain. The cost of an iron pipe, 6 to 10 in. diameter, is from 75 cents to $1.25 per foot run ;vitrified pipe will only cost about one half as much as iron pipe; and a stone box-drain, largeenough to allow a man to enter it for cleaning it out, will cost from $2 to $2.50 per foot run.Where the length of the drain is short and the fall limited, a box-drain will prove the mostadvantageous.
The protection of the side walls from the deteriorating action of the heat is usuallyobtained by a facing of firebrick, or of cast-iron or wrought-iron plates. Where an iron facingis employed, an air-space is left between the iron and the face of the side wall, which is a veryimportant element of the design. A cast-iron facing of the proper thickness will outlast anyother material, but it is liable to crack under the sudden changes of temperature, in additionto the shock from the jarring of passing engines. Wrought-iron wears or rusts more quicklythan cast-iron, especially when exposed to the combined attacks of heat and water. A fire-brick facing, if well laid in fire-clay and built so as not to receive the weight and jars of themoving load to an appreciable degree, will give good service. Firebricks are easily damaged,however, by contact with shovels and other tools, and frequent repairs and the subsequentrenewal of the facing would be eventually necessary. Where firebrick are not available ortoo costly, a facing of common hard brick will prove a cheap and efficient substitute for thefirebrick, it built so as to allow renewals without tearing down the entire side wall. Ordinarystone or brick walls are doomed to destruction in a comparatively short time. If built, how-ever, of first-class masonry, composed of large through stones, well jointed and bedded, andof a good heat-resisting quality, excellent results can be expected.
Thus far reference has only been made to stone or brick ashpits, or pits with large cast-iron chairs supporting the rails. All iron pits do not seem to have found favor in this coun-try, although, under certain conditions, they have advantages over others that should not be