Mercury Shower
   The Mercury Shower demonstration is sealed to the base plate of the pump with wax, and the system exhausted. Mercury is poured into the cup, and atmospheric pressure drives it through the pores of the oak plug (with the grain running lengthwise). The mercury comes out of the lower end of the plug in a shower of fine droplets that are charged by friction during the passage through the wood. The demonstration is done in a darkened room, and the shower emits the characteristic blue-white color of a modern mercury discharge tube as the droplets discharge on their way down to the collecting cup. This apparatus is at Middlebury College, and is illustrated in the 1860 catalogue of Edward. S. Ritchie of Boston at $1.00.

   This demonstration is a direct descendent of Otto von Guericke's observation in the sixteen fifties that a pressure difference of one atmosphere would drive water through the walls of a wooden barrel. Precautions have to be taken to keep mercury out of the pump mechanism, which is made of brass and therefore amalgamates easily. We are very unlikely to do this demonstration today because of the well-documented toxicity of mercury and mercury vapor. Scientists of the nineteenth century (and earlier) handled mercury in this and other experiments with no apparent realization of its dangers. Electrical apparatus routinely used exposed mercury contacts to secure freedom of motion, along with low contact resistance. Mercury poisoning was regarded as an acceptable, if unfortunate, industrial hazard. Remember that the Hatter in "Alice in Wonderland" was not mad; he suffered from "hatter's shakes", a tremor caused by the mercury compounds which he used in his trade.

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