A glass tube has one end in a dish of mercury and the other
end closed by a stopcock. The distance from the surface of
the mercury to the bottom of the stopcock is 850 mm. The
apparatus is at 25 °C, and the mercury level in the tube is
the same as that in the dish.
(a) Show on drawing (1) what the approximate level of
mercury in the tube will be when the temperature of the
entire apparatus is lowered from +25 °C to -25 °C.