The pots are shipped on three-wheeled trucks, which are re turned to the works, so that they are loaded and unloaded with ease and security, where before there was always great danger of breaking down. The work must be under most intelligent supervision.
When required for use, the pots are placed for four or five days in the annealing furnace, which is on the reverberatory principle, and they are there kept at a red heat. This furnace is so situated, that the pots, when ready, can be very quickly transferred to the main furnace—an operation of exceeding dif ficulty, and requiring great skill and dexterity, as they have to be removed whilst red hot, and it must be done so quickly that no sudden cooling shall injure the pot, a difficulty which can only be understood by remembering that the ordinary pots are nearly four feet in depth, are the same in width at the mouth by about thirty inches at the bottom, and they weigh several hundred-weight. The enormous amount of labor bestowed upon these pots makes them very expensive. Their removal from the annealing-oven to the main furnace is effected by an immense pair of forceps several feet in length, which are placed horizontally upon an upright iron pillar about three feet in height, which rises from a small iron truck on four wheels, so that the whole apparatus can be easily moved from place to place. By means of this instrument the pot is lifted and dex terously withdrawn from the oven, and as quickly transferred to its position in the main furnace, in which usually to or 12 are placed on a platform of fire-brick or stone, each pot being opposite to a small arched opening through which it can be filled and emptied. The entrance to the main furnace, through
which the pots have been introduced, is then closed, with a movable door of fire-brick, and covered over with fire-clay, to prevent the escape of the heat.
The material used in the construction of the arches, as well as walls of large glass ovens, is best produced from the Stour bridge or similar clay, which is carefully shaped into large slabs, and faithfully dried for more than a year ; but it is not burned in the kiln.
Some of the leading manufacturies of fire-brick keep on hand various sizes of jack brick, and are also prepared to make any special shape of jack or glass pot stopper that may be wanted, and keep them on hand for any customer using them regularly. For the crowns of furnaces, brick are made to any pattern that may be desired—but usually twelve inches long, with the lines tapering to suit the radial lines of the furnace. For those glass manufactures who have mills and are prepared to manu facture their own shapes, the fire-brick manufacturers keep a large stock of different clays on hand, calcined and green. The calcined clay should be all carefully selected and thoroughly burned.
For building the eyes of furnaces, repairing benches and mak ing flue-brick, etc., fire-brick manufacturers carry a stock of batch clay which should be prepared very stiff so as to require thorough ramming in order to get it securely in its place ; and the same stock when desired can be made into blocks to form the eye, and burned.