File:The electrical conductivity of commercial copper (1911) (14776270601).jpg

Identifier: elec71031301911148148wolf (find matches)
Title: The electrical conductivity of commercial copper
Year: 1911 (1910s)
Authors: Wolff, F.A. Dellinger, J.H.
Subjects: USA
Publisher: National Bureau of Standards
Contributing Library: NIST Research Library
Digitizing Sponsor: NIST Research Library

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
ct with the fixed knife-edges. A movable knife-edge was also provided, traveling along a steel scale graduated for103 cm. Its contact pressure is adjusted by a lever and weights.This knife-edge makes it possible to measure the resistance of asample of any length. Its position is capable of fine adjustmentby a cone and socket device, and is readable by means of a vernierto 0.1 mm. On account of the advantages of measuring samples against astandard of the same material in the same bath, frames for aux-iliary copper standards were provided. These standards werewires about a meter long, with soldered potential terminals. Sucha standard was placed in a frame, with its ends connected intosmall clamps, and its potential leads connected to binding posts.The two clamps and the two binding posts terminated in amalga-mated copper rods. Mercury cups in the marble base were soplaced as to receive these amalgamated terminals. When theframe was in place, the auxiliary copper standard lay parallel to
Text Appearing After Image:
Fig. 3. Conductivity Apparatus. Defunoer) Electrical Conductivity of Copper 113 the wire sample under measurement. The wire sample could beput into connection either with the auxiliary copper standard orwith a manganin standard in a separate bath, by means of amovable amalgamated copper link. All connections were car-ried under the marble to binding posts on one side of theapparatus. The apparatus was provided also with means for applying aknown tension to the wire under measurement. This consistedof a pair of pulleys at one end of the bath, with a pan and weightsfor attaching to a cord clamped to one end of the wire sample.The effect of tension has to be considered when measuring theresistances of small wires. Experiments showed that for anincrease of tension of 1 kilogram per mm2 cross section, the resist-ance increased 0.025 percent, which corresponds to an increase ofspecific resistance of 0.011 percent. For example, if a No. 18wire is under a tension of 1 kilogram, its resistance

Note About Images