. American engineer and railroad journal . a cubic inch of the metalliciron. ; In the case of both the primary and secondary crystals thepredominant well-defined angles of the facets of the crystalshovered more or less about the angle of 120°. The majorityof the angle readings, made with the goniometre attached tothe microscope, indicating generally a hexagonal structure onform of crystallization. There wore, however, also perfectcubical crystals observed. * The observations were made with a Ross first-class micro-scope. The micro-measurements afford an indication of thecomparative size of the
. American engineer and railroad journal . a cubic inch of the metalliciron. ; In the case of both the primary and secondary crystals thepredominant well-defined angles of the facets of the crystalshovered more or less about the angle of 120°. The majorityof the angle readings, made with the goniometre attached tothe microscope, indicating generally a hexagonal structure onform of crystallization. There wore, however, also perfectcubical crystals observed. * The observations were made with a Ross first-class micro-scope. The micro-measurements afford an indication of thecomparative size of the primary aud secondary measurements were carefully taken by a Jacksonmicrometre, and in some cases by a Ramsdcn screw microme-tre, both accurately calibrated with a standard stage microme-tre. The wrought-iron forgings on which the observations weremade were constituted of practically pure hammered wroughtiron, the dimensions of fhe mass being about 10 ft. long andabout 12 in. square. The great length of time required for. such large masses of iron to cool from a white heat appearedto facilitate the production of the crystals of the secondaryformation. fiThe rationale of this duplex crystallization has apparentlybeen as follows : The mass of metallic iron on cooling havingreached the crystallizing point at about 740° C, the peripheryor skeletons of the larger or primary crystals were then the period of cooling was, however, very slow, the semi-fluid or viscous metal in the interior of these primary crystalswas, on finally consolidating, apparently further broken up orsubdivided into a considerable number of smaller crystals, en-closed within the boundary or periphery of the primary crys-tals. In the course of further experiments on the cooling of largemasses of wrought iron, the author has also found, by theuse of high power objectives, that the secondary crystalssometimes enclosed a still more minute form of crystals ofpure iron, of the cubical form,
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
