Big Barometer
This is a demonstration of a potassium mercury iodide barometer [more precisely, a barometer made from an aqueous solution of potassium tetraiodomercurate(II)]. To make a potassium mercury iodide barometer, the liquid is poured into a long glass tube. It will take approximately 1 liter of solution to fill the barometer. Air bubbles are forced to the top by tapping the tube. The tube is topped off with a dropper. A rubber stopper is placed at the end of the filled tube and the tube is stood up while holding the stopper in place.
Additional potassium mercury iodide is added to a dish at the bottom until the opening of the tube is under the level of the solution. The stopper is removed and the solution flows out until the pressure of the surrounding air is equal to the pressure exerted by the solution at the bottom of the column. This barometer is about eleven feet tall.
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