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.