Britain at Work
A Pictorial Description of Our National Industries

HOW GAS IS MADE. 97 heat, and in large of men are allowed rod, turned briskly, and pulled out empty with a flourish ! The whole process is so deftly and system- atically performed that probably about the same amount of coal is shot into the retort on each occa- sion. The perform- ance is gone through twice for each retort, and by this method the vessels are charged according to their capacity for yielding the best results. The w o r k is arduous in the great establishments a group a spell of rest at the lapse of each half-hour, their shift of work occupying about eight hours before they leave. But, again, in some works machines running on rails in front of the lines of doors are used to rake out the glowing coke and re-charge with fresh coal. Six hours is about the length of time which the coal is allowed to remain in the retorts to give off its gas. The retorts are usually made of the most stubborn fireclay, and are three inches or so in thickness. I hey are built together very solidly over furnaces, and are almost continuously kept white-hot. 1 he heat of the furnaces is in- tense, being considerably over 2,000 degrees Fahr. The temperature may be tested in an interesting manner by placing a piece of platinum in the furnace and, when hot, plung- ing it immediately into water ; the rise in temperature of the water is then taken, and an approximate estimate formed of the heat in the furnace. But we must follow the adventures of the gas. It rises from the heated coal in the closed retort, and escapes through the pipes to the large black box above, which contains tar water, and is called the hydraulic main. I he pipes dip into the water, and by this arrangement the gas is prevented from returning to the retort. Both tar and water are condensed from the gas, and an 13 Photo; Cassell & Co., Ltd. overflow pipe leads them down to the tar well. But the gas itself passes on by a pipe running out from the overflow pipe above the tar well to the condensers. These consist of an arrangement of numerous bent pipes, of which there are several types, kept cold, their frigidity causing more tar to be collected, and from these pipes the tar slowly trickles down to a tar well. After passing through the condensers the gas is still very impure, and has to be washed and scrubbed, and treated with lime to free it from its ammonia and sulphuretted hydrogen. The “ washer ” consists essentially of a suit- able receptacle containing water, and the gas is simply sent through this water, which dissolves some of its impurities ; but in the “ scrubber,” through which it next passes, it is led up a large pipe or tower filled with deal boards, or with coke having water trickling over it. The washer and scrubber are com- bined in some manufactories, but in any case the water soon smells strongly of ammonia, and indicates the quantity of that chemical which is being extracted from the gas. Again, by another system of scrubbing, the gas is drawn up through a confined space through which spray is made to descend. An “ exhauster,” consisting usually of a fan or pump, which is fixed further on—