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GROVES AND THORP'S
APPLIED TO ARTS AND MANUFACTURES
This, the third volume of Chemical Technology, gives a history of the manufacture of gas and its application to the purposes of illumination. As distinguished from oil, wax, and fats, which have been employed from the earliest times as sources of artificial light, the use of gas for this object is not yet a century old, at all events in this country, and although electric lighting is more convenient and cleaner than gas, the introduction of the Welsbach and other incandescent burners, aided by the relatively low cost of gas, will no doubt enable it to maintain the important place it occupies as an illuminating agent.
The first portion of the work is devoted to the history of gas lighting, and statistics are given illustrating the very large amount of capital employed in this important manufacture, and its vast extent; numerous analyses of various gas-coals being also quoted.
The process of carbonisation of coal is then considered, showing the different products formed, and the effect on carbonisation produced by variation in temperature. This naturally leads to the methods employed, and there are full descriptions not only of the retorts and the various methods of closing them, but also of the furnaces in which they are heated. The latter are considered in historical order, ending with the most recent recuperative or regenerative furnaces and the machinery now often employed in large gas works for mechanical charging and drawing the retorts, an operation which was formerly always done entirely by hand. The use of machinery has the advantage not only of dispensing with a large amount of manual labour, but also of distributing the coal very evenly in the retorts, and consequently of providing for a more equable and thorough carbonisation.
The methods proposed for the removal of the tar and other subsidiary products are next discussed, and the kinds of condensors and tar-extractors in general use are fully described. A short chapter follows on the exhausters used for diminishing the pressure in the retorts, and then the various washers and scrubbers employed for removing the ammonia from the cooled gas are illustrated and their construction and mode of action explained, stress being laid on the very important part played by the ammoniacal liquor, in the more recent purifying machines, in removing