Comprising a 360mm x 210mm rectangle of 22mm diameter glass tubing.In use the tube is mounted vertically in a retort stand. Convection currents may be generated by gently heating one of the lower corners of the rectangle and a small amount of potassium manganate(VII) crystals dropped into the tubule will act as an indicator. It is made from borosilicate glass and can withstand temperatures up to 500 degrees.Clamps not included.