REFRACTORIES FOR GASWORKS PURPOSES 203
(3,360° F.). The main feature of the apparatus is the special type of Méker burner, requiring compressed air under a pressure of from 10 to 30 Ib. per square inch; wliilst, for effective results, the gas pressure should not be below 1| inches.
Fig. 107.—The Mbkeb Aie-Gas Ftonaoe.
A crucible of special refractory material is mounted on a support, and the flame from the burner, passing through the base of the support, surrounds the crucible, and is then turned downwards to its outlets.
Seger cones (Fig. 108), which partially fuse, or “ squat,” at predetermined tem peratures, are found to provide th.e most convenient means of recording the approxi
mateyielding points of the samples under test. The Refractory Materials Committee state that two or more tests are generally required when an unknown material is being dealt with. “ A preliminary trial is first made with a piece of the material chipped into the approximate form of a cone. This should be cemented. on to the refractory slab of the test furnace with. a
mixture of alumina and best china clay, fiG. io8.—Sbgbk Conbs.
together with Seger cones 28, 30 and 32
(small size). Best china clay fuses between cones 35 and 36 ; and all British fire-clays fall below this point. If cones 28 and 30 fall, the furnace should be cooled, and th.e material under investigatioQ examined. If it exhibits no sign, of fusion, the trial should be repeated with.con.es 30, 31 and 32. By this method of approxi-mation it is possible to decide whether the piece vitrified between cones 30 and 31 or between cones 31 and 32. The cones should, in all cases, be placed relative to the sample so that both are subjected to the same temperature. It should be