The operations are carried on in large cast steel crucibles, and the charges consist of caustic soda and a finely ground artificial compound of carbon and iron, which is the reducing agent. This compound is made by coking a mixture of fine iron and pitch. The crucibles containing these materials are first heated in a small furnace at a low temperature, the object being to expel the hydrogen from the caustic alkali and bring about quiet fusion. The crucibles are then removed from this furnace, by means of a little truck, and placed upon a movable platform, which is operated by hydraulic power. They are then by this means raised into the large furnace, where the crucible covers are fixed stationary. The edges of the crucible and cover coming together form a tight joint, and from this cover projects a small tube to the outside of the furnace into a narrow rectangular box, known as the condenser. The reduction of the sodium commences soon after the crucible containing the charge is in its place, the vapors and gases passing from the fused mixture through the exit pipe from the cover into the condenser, where the metallic vapors are condensed to metal, while the uncondensed gases escape by a small outlet tube. After the charge is exhausted, the crucible is lowered, and one containing a fresh charge raised in its place; in this manner the process might almost be called continuous.
The actual temperature used in this process to bring about reduction, as measured by experts, has been found to be 850° Cent. By the older method the temperature necessary is about 1,400° Cent. This is practically the great point of economy in this process, as the high price of sodium has hitherto been owing to the excessive heat used in the older process and the consequent destruction of the wrought iron vessels. Sodium at present costs about four shillings per pound to produce, while the materials necessary for this quantity, were nothing wasted, would hardly cost four pence. The difference between these two figures represents the wear and tear to the furnace, the destruction of the wrought iron cylinders, the loss and waste of materials, the excessive labor and care necessary to employ in manufacturing, and fuel. Approximately, the cost of these items in producing one pound of sodium by the older process is as follows: