File:The practical telephone handbook and guide to the telephonic exchange (1906) (14569424970).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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Text Appearing Before Image:
Fig. 66
Text Appearing After Image:
Fig. 67 owing to their general adaptability, have nearly supplantedall other forms for general use. For a long time they labouredunder the disadvantage of what is known as packing,which resulted from the gradual settling down and consoli-dating of the carbon granules, so that the loose contacts, upon 78 PRACTICAL TELEPHONE HANDBOOK which their efficiency depended, were no longer existent, andthe carbon conducted as an ordinary solid conductor. Many different forms of granular microphones have beendevised, but nearly all represent different methods of gettingrid of the packing difficulty. They all contain crushed retortcarbon or oven-coke sifted through wire gauze so as to obtaineven grains of about the size of those of fine gunpowder.A quantity of this is enclosed in a small cell between a flexiblediaphragm and a fixed block of carbon. Probably the bestmethod adopted for the prevention of packing is repeatedsifting, to ensure that all the granules used in a transmitterare as nearly of

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