This apparatus comprises a rectangle formed from 20mm diameter borosilicate glass tubing, for demonstrating thermal convection in water.
The tube should be filled with water and the apparatus carefully mounted using a retort stand with clamp on either side. A few crystals of potassium permanganate (or some drops of concentrated coloured dye/ink) can then be introduced into the open top of the tube, whilst one of the bottom corners is heated gently with a low Bunsen flame. As heat rises up this side of the tube, colour from the crystals or dye will begin to move along the top and then down the opposite side, due to the convection currents generated. Finally, the coloured water will move along the bottom of the apparatus and back up the side above the heated corner.
Dimensions: 380 x 300 mm approx.