at the top, built entirely of fireclay bricks.

The end of the lower tube rested on a fireclay ladle nozzle, and was properly jointed with fireclay; through this nozzle the steam or air was supplied to the inside of the refractory tubes.

Their ends are connected at the top to two conductors, which pass down inside the tube and end in a fireclay plug at the bottom.

The principle is applied in the following manner: A cylinder of fireclay slides in a metal tube, and has two platinum wires one one-hundredth of an inch in diameter wound round it in separate grooves.