[Physics] Which oil was used by Robert A. Millikan in his oil drop experiment

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I need to know which oil was used by Robert A. Millikan in his oil drop experiment, i.e.name of oil or chemical formula of the oil molecule.

Best Answer

The name, as far as I can find, is "highest grade of clock-oil" as mentioned in his 1913 paper (page 111, last line). The density of this oil at $23\, {}^\circ \mathrm C$ is $0.9199$, but the units aren't mentioned.

EDIT: I went to look up an earlier work (1911) and found two other oils of interest that were used, namely "cleaned gas engine oil" of density $0.9041$ and the more volatile mineral oil (machine oil) of density $0.8960$, both measured at $25\, {}^\circ \mathrm C$. I believe these are the oils the Wikipedia entry alluded to.

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