Convection Apparatus for Gases (303-1) The enamel coated metal box has a sliding glass front and two glass chimney stacks. Smoke is introduced in one chimney using either smoldering paper or a punk stick. The smoke can be observed traveling down into the box and back out through the other chimney that stands over a flaming candle. The principles of convection currents and wind is made very clear through this demonstration. Qty :