Hood—Circular sheet-iron hood from 120 to 130 mm in diameter the height of the lower perpendicular side to be from 50 to 53 mm; provided at the top with a chimney 50 to 60 mm in height and 50 to 56 mm in inside diameter, which is attached to the lower part having the perpendicular sides by a cone- shaped member, bringing the total height of the complete hood to 125 to 130 mm. The hood can be made from a single piece of metal, provided it conforms to the foregoing dimensions. As a guide for the height of the flame above the chimney, a bridge made of approximately 3-mm iron or Nichrome wire, and having a height of 50 mm above the top of the chimney, shall be attached.