Modern Gasworks Practice

374 MODERN GASWORKS PRACTICE the ventilating shafts, by the formation of a draught, supply the necessary oxygen for sustaining and augmenting the fire. Ventilation, therefore, is liable to cause great mischief. Perhaps, taking everything into consideration, it is wiser to adopt surface ventilation only. Owing to the greater tendency of some coals to fire, it is as well to keep the various classes in distinet heaps as far as possible. Experience has shown that it is inadvisable to stack all the large coal in one heap ; for probably, owing to disintegration, a “ dust-pocket ” will be formed somewhere towards the bottom. The spaces between. tlie lumps afl'ord excellent opportunities for the creation of a draught, and, consequently, a steady supply of air to the pocket. In such a case we get conditions similar to those occurring with insufficient artificial ventilation. The heap should be piled so that lump and fine are distributed as evenly as possible. A point which usually escapes observation is the tendency of the large lumps (when tipped on the apex of a heap) to run to the outside, leaving the centre of the heap composed of slack. This is undesirable, and the coal- should be spread out as the heap is built up. English coal spread out in this way was stacked at Berlin to a height of 46 feet for more than twelve months, and no trouble was experienced with it. The depth of the heap is another point which has received a good deal of attention. Ac-cording to information available, it appears that there is some relation between the liability to spontaneous combustion and the height and volume of the heap in which it occurs. There also appears to be a “ critical height ” above which it is inadvisable to go, and for ordinary gas coals this ranges between 15 and 20 feet. Excessively high, heaps should, of course, be avoided as far as possible, for pulverization is sure to take place towards the bottom. The British. Fire Prevention Committee recently issued a special warning in regard to the storage of coal in bulk with. special reference to spontaneous combus-tion. The following precautions were included :— (a) Stacks should not be higher than 10 feet. (6) Iron perforated pipes 3 or 4 inches in diameter, or, failing these, either suitable earthenware pipes or duets formed of incombustible material should be inserted vertically in the Stacks as they are built up. The lower ends of these pipes, or duets, should be at different heights from the ground throughout the Stacks. There should be one pipe or duct to about every 300 square feet of surface. (c) A thermometer should be lowered occasionally through these pipes or duets to ascertain the temperature at the centre of the stack. (t?) If wet, very small, very soft, or impure coal is received, it should be dumped around the edges of the stack, or in some location where the air can get to it freely and where other coal will not be packed on top of it. The United States Bureau of Mines states that in making a coal pile of mixed sizes, the coal should be so håndled as to make a homogeneous pile and prevent the segregation of coarse and fine coal. This frequently determines the most desirable machinery for unloading coal. It is common practice to limit the height of a coal pile for two reasons :—-A. pile too high crushes the lower layers of coal, producing more fines ; the larger the