. Spons' dictionary of engineering, civil, mechanical, military, and naval; with technical terms in French, German, Italian, and Spanish . if not too muchmixed with metallic oxides, or with too much mica. The quantity of quartz determines therefractibility of the stone. This material is very convenient, because in most instances it is easilyquarried and dressed to the desired forms. Chlorite slate, gneiss, porphyry, granite, and similarsubstances, resist fire in some instances very well ; but their quality depends entirely on a peculiarcomposition. As a rule, these rocks are not very refractor
. Spons' dictionary of engineering, civil, mechanical, military, and naval; with technical terms in French, German, Italian, and Spanish . if not too muchmixed with metallic oxides, or with too much mica. The quantity of quartz determines therefractibility of the stone. This material is very convenient, because in most instances it is easilyquarried and dressed to the desired forms. Chlorite slate, gneiss, porphyry, granite, and similarsubstances, resist fire in some instances very well ; but their quality depends entirely on a peculiarcomposition. As a rule, these rocks are not very refractory, and are all liable to be broken byheat. Artificial Stones ; Fire-brick.—When natural stones cannot be obtained, or the purpose requiresothers, the substances of which artificial stones are composed, such as clay and silex, are pounded,ground together, and formed into bricks or slabs of any form that may be desired. Quartz, whichis most in use, and in fact the only available substance besides clay, is pounded in stamping mills,such as represented in Fig. 2982. This operation is either performed dry, which causes much dust i;vVI and premature destruction of machinery, or it is done by passing a current of water through thestamping box, and gathering the sand in a trough, in which it settles, and tlie water flows ofl. Ifthe quartz is hard, such as river pebbles, or milky quartz, it may be exposed to a red heat in aroasting heap, after which it may be pounded quite easily. 5 F 1538 FOUNDING AND CASTING. Of quartz, thus coarsely pounded to tlie size of a grain of wheat, or smaller, three parts aremixed with one part of plastic fire-clay ; the whole well soaked with water, and diligently mixed,forms an excellent fire-proof sandstone, when merely air-dried Of this mixture, bricks and slabsare easily formed, which may be used air-dried, in reverberatory, puddling, reheating, and all suchfurnaces, where no actual work or rubbing is done on the surface of the brick ; for thou
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Keywords: ., bookcentury1800, bookdecade1870, bookidsp, booksubjectengineering
