Bridge transfer and short arc transfer at contact separation
Bridges in opening metal contacts have been observed a long time ago. Sundorph , in 1903, and particularly Angelica Szekely , in 1924, studied such bridges. The latter worker stated that the material of the bridge was derived from the anode, and that the bridge always attained such dimensions that its voltage finally remained constant, of the order of 0.5 to 1 V. Visible bridges were easily obtained between iron electrodes. Her publication was little observed. In 1938, the bridges were rediscovered and studied by Betteridge and Laird . They succeeded in photographing stabilized molten bridges between platinum contacts. They showed that the final bridge voltage, before rupture, was of the order of 0.7 to 2 V, depending on the contact metal. They also observed that the hottest section is not in the midst of the bridge. They assumed the Thomson effect to be responsible for the displacement. However, R. Holm  remarked that the Thomson effect, at that time measured on solid metals only, had the wrong direction for an explanation of the displacement in platinum. In the following, the Thomson effect can be accepted as the cause of the displacement in platinum because Llewellyn Jones has shown that with platinum contacts the effect changes its sign when the metal melts; see Fig. (66.02).
KeywordsMigration Platinum Boiling Galn
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