Journal of the Association of Engineering Societies . and the tar is drained off from the bottom of thehydraulic main. This water also absorbs a portion of the ammoniathat is present in the gas as an impurity. The special purpose ofthis hydraulic main, however, is to automatically prevent the gasfrom going back from the holder into the retort, when the mouth-piece is open for the purpose of drawing the coke or charging theretorts with coal, acting much after the fashion of a check valve., The pressure in the retorts necessary to force the gas throughthe water in the hydraulic main and the seve
Journal of the Association of Engineering Societies . and the tar is drained off from the bottom of thehydraulic main. This water also absorbs a portion of the ammoniathat is present in the gas as an impurity. The special purpose ofthis hydraulic main, however, is to automatically prevent the gasfrom going back from the holder into the retort, when the mouth-piece is open for the purpose of drawing the coke or charging theretorts with coal, acting much after the fashion of a check valve., The pressure in the retorts necessary to force the gas throughthe water in the hydraulic main and the several pieces of purifyingapparatus into the holder is so great that there is a considerable lossin the yield of gas, unless relieved by the introduction of a suctionpump, known as an exhauster. This exhauster is usually connectedup in the line of the main gas off-take pipe immediately beyond theretorts. The exhauster is so constructed and the supply so regu-lated that any desired pressure can be kept in the hydraulic mains GAS. 91 ? M -W *>] < 1. 92 ASSOCIATION OF ENGINEERING SOCIETIES. at all times. After the gas has been drawn out by and has passedthe exhauster it is put through a condenser for cooling, in which agreat deal of the tarry globules or vapor is thrown down and drainsoff to the tar well. Then it usually passes through some furtherform of tar extractor or washer, where the remaining particles oftar should be removed. Thence it passes through the scrubber,where it is brought in contact with water, which absorbs theremaining portion of ammonia in the gas. After the gas hasleft the scrubber it should need but one more purification, and thatis the removal of the sulphur compounds which usually appear inthe form of sulphuretted hydrogen and bisulphide of carbon. Thesesulphur compounds were formerly removed by quicklime mois-tened and placed upon trays in large cast-iron boxes, the gas beingforced through this lime. In later years the lime has been practi-cally aband
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectenginee, bookyear1881
