Identifier: railroadconstruc04webb (find matches)
Title: Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools
Year: 1913 (1910s)
Authors: Webb, Walter Loring, 1863-1941
Subjects: Railroads
Publisher: New York, J. Wiley
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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jectionable at high speeds,being mutually destructive to the rolling stock and to the frog.The jarring has been materially reduced by the device of ^springfrogs—to be described later. Frogs were originally made ofcast iron—then of cast iron with wearing parts of cast steel,which were fitted into suitable notches in the cast iron. Thisform proved extremely heavy and devoid of that elasticity oftrack which is necessary for the safety of rolling stock andtrack at high speeds. The present universal practice is to buildthe frog up of pieces of rails which are cut or bent as required.These pieces of rails (at least four) are sometimes assembled byriveting them to a flat plate, but this method is now but littleused, except for very light work. The usual practice is nowchiefly divided between bolted and keyed frogs. In eachcase the space between the rails, except a sufficient flange-way,is filled with a cast-iron filler and the whole assemblage of parts § 255, SWITCHES AND CROSSINGS. 291
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Plate VIII.—Some Types of Frogs. 292 RAILROAD CONSTRUCTION. § 255. is suitably bolted or clamped together, as is illustrated in PlateVIII. The operation of a spring-rail frog is evident from thefigure. Since a siding is usually operated at slow speed, whilethe main track may be operated at fast speed, a spring-rail frogwill be so set that the tread is continuous for the main track andbroken for the siding. This also means that the spring-rail willonly be moved by trains moving at a (presumably) slow speedon to the siding. For the fast trains on the main line such afrog is substantially a ^fixed^ frog and has a tread which ispractically continuous. 256. To find the frog number. The frog number (n) equalsthe ratio of the distance of any point on the tongue of the frogfrom the theoretical point of the frog divided by the width ofthe tongue at that point, i.e. =hc-^ah (Fig. 130). This valuemay be directly measured by applying any convenient unit ofmeasure (even a knife, a short pencil,

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