An apparatus for investigating contact charging by mercury

It is often difficult to interpret experiments on contact charging of insulators by metals because the area of true contact is not in general known. The problem can be circumvented by using liquid mercury as the contacting metal, since mercury will form an intimate contact if the insulator surface is not too rough. The authors describe an apparatus which allows contacts of well defined and reproducible area to be made. Using this equipment they have been able to show that the charge accumulation which occurs when hard metals are repeatedly contacted to insulators does not occur with mercury contacts.