From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Observation on the effects of current on electrical contacts, specifically regarding resistance and discoloration.
| Identifier | ExFiles\Box 35\5\ scan 145 | |
| Date | 20th October 1920 | |
| Contd. -2- EFC3/T20.10.20. blackened uniformly over the contact area, and the negative turned brown. With the circuit again arranged to pass 10 amperes, when unground and undiscoloured points were in contact, it was found that with these discoloured faces placed squarely in contact, only from 7.5 to 8.0 amps. passed. This was also found to be the current when the discoloured positive face was pressed against the side of the negative rod, but if the discoloured negative face were placed against the side, nearly the full 10 amperes would flow. This would appear to demonstrate that the exide formed on the positive rod has considerable resistance, whereas the negative dis- colouration has very little. Neither film showed tendency to flake off, but reversing the polarity and repeating the inductive sparking very quickly reversed the two discolourations. EFC. | ||