GLASS-MAKING. The Siemens Continuous Tank-Furnace.—The use of the melting pots in glass-making is now altogether abandoned, and the batch is introduced into, melted in, and worked from a tank occupying the entire bed of the furnace, which let ter is heated by the well-known Sie mens regenerative gas system. Two floating bridges or partitions divide the tank into three compartments—the melting compartment, the COM pertinent, and the working-out com partment. In the illustration, Fig. 1 is a longitudinal section of the furnace, and Fig. w is a transverse section taken through the melting compartment look ing toward the rear of the furnace.
The raw material (or batch) is fed into the melting compartment through the door at the back end of the furnace, and the partially melted glass passes under the floating bridge into the refining compartment, where the metal, by the influence of the higher tem perature maintained upon its surface, is completely purified, and sinks to flow under the other bridge into the working-out compartment in a thorough workable condition. Air-pass ages are provided to maintain the sides of the tank at the requisite temperature to prevent any egress of glass through them. and the floating bridges are renewed as often as they be come burned out. The flames play across the furnace from the gas and air ports, which lead to the regenerators of the regenerative gas-furnace. In order to regulate the temperature of the different parts according to the various stages of preparation of the glass in the several compartments, the gas and air ports are constructed of larger or smaller dimensions, or their number varied according to the amount of heat required at the different points. This is also facilitated by means of division walls (not shown in the illustrations), which may he built over the floating bridges to separate the compartments. The temperature of the working-out com partment is further controlled by regulating the draft of the furnace chimney, by diminishing which more or less flame must necessarily pass over the bridge into this compartment from the refining compartment.
About the first improvement made on the Siemens continuous tank-furnace just described was the idea of Mr. Frederick Siemens to construct the tank in the form of a horseshoe or segment of a circle, with the feed ing-door and COMMMlientions to and from the regulator arranged on the flat side of the segment, for the purpose of cooling the ex terior surface of the tank and ren dering it available for working out holes. He also arranged a series of working-out compart ments on the inner side of the curvilinear wall, each compart ment communicating by means of a passage with the meliing-cham hers. In the continuous refining and working-out of glass it also became necessary to remove or avoid the impurities which were found to float upon the surface of the liquid in the tank or pot, and therefore Dr. Siemens contrived a device to do that important work in a simple and inexpensive way-. He constructed a fire-clay vessel or boat of oblong shape to swim in the liquid glass contained in the tank, and this boat was perforated below its draft-line so that, as it floats, the melted material flows into the boat through these holes entirely free from the im purities floating on the surface of the liquid in the tank or pot. TO further• assist the process of fining and working-out of the glass, the boat is made in two compartments, the second of which is the w•urking-ont compartment: the dividing partition is provided with apertures near its hot tom, so that, as the glass flows into the boat free from impurities, as shove de scribed, it becomes more fluid in the first compartment by the action of the heat upon its surface than below, and consequently, in becoming denser, it sinks to the bottom of this first compartment, whence it flows through the apertures named into the second compartment, which is within convenient reach of the working-out hole of the furnace.