The adsorbed water vapor upon the surfaces of fused quartz and mercury was shown to have a decided effect upon the triboelectric charge produced upon the surfaces. When the water vapor was expelled from the quartz surface by proper heating and exposed surface of the mercury cleaned by distillation, the triboelectric charge was reproducible and was 1 E.S.U/cm2 within the limits of error of the experiment. The method of making contact was shown to have an effect upon the magnitude of the triboelectric charge.
L. H. DAWSON, "TRIBOELECTRICITY OF QUARTZ AND MERCURY," J. Opt. Soc. Am. 18, 344-347 (1929)