The variation with current and inductance of metal transfer between platinum contacts

The investigation described is a continuation of the work on transfer between platinum contacts published by the author in a previous paper. An account is given of the manner in which the metal transfer between platinum contacts breaking a 6-volt circuit varies with current and circuit inductance. Curves of the net transfer are given for currents and inductances in the ranges 1.8¿7.6 amp and 0.06¿117 ¿H respectively. The net transfer consists of up to four different types of transfer superimposed one on another, namely ¿bridge, ¿ ¿short arc,¿ ¿long arc¿ and ¿reversed short arc¿ transfers. The existence of the fourth type of transfer had been observed previously by Dr. A. L. Allen for currents of 10 and 20 amp, but was not known to occur at currents as low as 2 amp. It is shown that the build-up of pips on the contacts varies in steepness with the nature of the transfer. Some suggestions are given as to the mechanism of the different types of transfer, but at present a complete explanation cannot be given. Consideration is given to the practical application of the results, and it is shown that under some conditions the life of platinum contacts could be improved by controlling the effective circuit inductance at break to a value of about 0.6¿H.