Convection Tube
Product Details:
Dramatically demonstrate the motion caused by the convection in a liquid. Fill this glass apparatus with water, then introduce a dye at the top. Heat one of the lower corners, and watch as the dye follows the path of the convection current. 
Apparatus is glass and measures 15 × 20 cm. Food dye is available separately. Includes a Physical Science Fax with demonstration instructions, a detailed discussion and a reproducible student worksheet.