Spare Chimneys

This is also known as the mine shaft apparatus, as it uses the same principal which was historically used to ventilate metal mines. The candle represents the furnace which was used at the time (early 19th century) to heat air at the bottom of one of the mine shafts, causing stale air it to rise up to the surface. The consequence of this was that fresh air was drawn down another shaft and into the mine, to ventilate it.
The apparatus consists of a metal box with a sliding glass plate at the front, with two glass chimneys mounted above holes in the top of the box (the ‘mine shafts’). A small candle or tea light is then placed below one of the chimneys and lit. The heat from the flame causes warm air to rise up the chimney, due to the convection currents created, resulting in cooler air then being drawn down the other chimney to replace it. In order to visualise the movement of air, a smoke match or smouldering piece of cardboard or string can be held close to the opening of the chimney which does not have the candle underneath; the smoke can then be seen being drawn down into the box and back out through the other chimney.
Dimensions: 220 x 100 x 165 mm approx.