These drying floors, or " drying stoves," as they are called in Great Britain, are each 120 feet long by 36 feet wide.
Although the stoves are fired from one end, there is a uni form temperature maintained in them throughout their whole extent. This result is accomplished by having an arrangement of double floors, with cold-air passages between them half way up the stove. By this system of heating Mr. Dunnachie ob tains the most perfect control of the temperature of the stoves, even though an iron floor is used, an object long aimed at and often attempted, but `now successfully accomplished. In ordi nary practice there is no deterioration of the brick. No over heating takes place, consequently no cracking of the brick, and therefore they go far sounder to the kiln than is usually the case. Owing to the special mode of arranging the dampers, each stove can be worked in stripes, to be strongly heated, if necessary, or mildly when sharp firing is not desirable.
Owing to the successful way in which the drying operation is conducted, those brick which are made one day are ready the next day for the kiln, whither they are at once carried direct without any piling. As there is thus no unnecessary handling, the chipping or other injury which brick frequently meet with while unfired or in the green state is reduced to a minimum.
The air-flue at front is closed by a slab, which is tilted around so as to make the openiqg large or small, as may be required. This is a better and cheaper arrangement than a close door.
Some of the older fire-brick works in the States of Ohio and Pennsylvania have in use hot-floors, which are constructed as follows : Across the end of the floor, which is nearly always rectangular, is dug a pit some six feet below the general level. In the wall of this pit are set fireplaces at intervals of from five to six feet. The fireplaces proceed inward about a yard, and then break up into from three to five parallel flues. These flues are about ten inches square, and are separated by four inches of brick. The flues traverse the whole distance of the floor and unite in a chimney or chimneys at the other end, which must be high enough to make every individual flue draw. These flues are covered by square tile twelve inches on a side ; the tile are placed four thick at the fire end of the flue, and run down to one tile at the opposite end. This is done to equalize the heat of the floor. The depth of the flues is so arranged that their unequal covering brings the tile to a level plane ; on this is spread a cement adapted to this use ; it is made of basic furnace cinder and sandy clay in equal parts, ground fine, and wet. If the cinder is not basic enough, lime is added ; the
mixture sets very hard, and will last four or five years if well treated. Sometimes the flues are covered with one thickness of tile all over, and are then leveled up with sand and another layer of tile. This is undoubtedly cheaper, and is also as even a distributor of heat as a plain tile floor would be, but is rather more apt to cause trouble in repairing by blocking up the floors with sand.
Conveying Fire-Clay. The most economical and expeditious methods of handling fire-clay at the mines, and conveying it from the mine to the factory, are of great importance, as the continuous operation of work during both winter and summer often depends on the means used to transport the clay.
The Union Mining Company, Mount Savage, Md., has had much experience in the handling of fire-clay. The clay mine of that company is situated on the south side of Savage Moun tain, three miles from the works by the tramroad. The bed of clay crops out along the summit of the mountain, and runs nearly northeast and southwest. The only other mine on this bed is a very small one, two miles from that of the Union Min ing Company. The clay from this mine is brought to Frost burg, where it is manufactured into brick.
The large bed was first opened on the out-crop, and for a number of years all the clay was dug from open pits, and hauled at great expense down the mountain in wagons to the works. Finally, when this method of mining had been carried on as long as was economical, the mine began to be worked systematically, and the levels were driven on the out-crop, on one side, wherever it could be reached by reason of the forma tion of the hill. From this level, galleries were driven at an angle up on the bed, clear through to the old workings. Chambers were driven out from these galleries, connecting the galleries as often as the ground would permit. When these chambers are all driven through, that part of the mine is robbed of as many of the pillars between the chambers as it is practicable and safe to remove. There are several of these levels driven, the last one about 100 feet below the next above, and as the bed dips about one foot in every four on an average, one can calculate on the amount of clay each level will yield. From the present outlook there is enough to run the works for a great many years.