File:The practical telephone handbook and guide to the telephonic exchange (1906) (14569529900).jpg

Identifier: practicaltelepho00pool (find matches)
Title: The practical telephone handbook and guide to the telephonic exchange
Year: 1906 (1900s)
Authors: Poole, Joseph
Subjects: Telephone
Publisher: New York, Macmillan Co.
Contributing Library: Northeastern University, Snell Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

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Fig. 382.—GlazedEarthenware Duct UNDERGROUND WORK 3B5 over both the concrete and cast-iron conduits, as the shortlengths used allow of slight curves being negotiated to avoidvarious obstructions met with. It has also the advantage overconcrete conduits of being practically gas and water proof.It is, however, considerably more expensive than the concrete-block conduit, when several ducts are required. Fig. 383 showsa section through 30 ducts. The practice in the Post Office
Text Appearing After Image:
Fig. 383.—Method of laying Earthenware Ducts is to use cast-iron pipes where only 5 ducts or under are requiredand earthenware ducts for more than that number, as this isfound to be the economic dividing line. American Practice.—In America wooden ducts of variouskinds are much used, the wood being protected from decay bycreosoting or by tar asphalt. One kind, known as the box conduit, is made up in the form of a series of troughs, likeendless pigeon-holes of square section. Another kind is madeof single tubes of either round or square external section, andcalled pump-log ducts. The Valentine conduit is 386 PRACTICAL TELEPHONE HANDBOOK made up of wooden blocks with several semicircular grooves.These blocks fit one over the other, and form a number ofcircular ducts, as shown in Fig. 384. Ducts made of compressedwood pulp or paper coated with asphalt are also used. All the above ducts are, when laid, embedded in concrete.Cement-lined ducts are also much used, formed of a thin wrought

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