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60                        METALLURGY   OF   CAST   IRON.
Dolomite is now being used in the making- of high silicon and other irons, but it is said it is not as effective in lowering sulphur in iron as limestone where sulphur is troublesome.
The more silica a flux contains the greater fuel or higher temperature required to fuse it and the less its value as a flux, for the reason that more lime is required to unite with the silica to make a good slag, and the more silicious the ore the more lime generally required to flux it. It has been known to require more lime than there was ore charged in order to flux the high silica which the ore contained! Silica as found in slag is not only derived from the fuel and ore, but also from the scale and sand of any iron which may be charged into a furnace or cupola, and from the oxidation of the silicon in iron during the heat. It is to be remembered that the more lime a flux contains, the better it serves the end of creating slag- to affiliate with the earthy matter and debris formed in a furnace or cupola, and also the more silica or lime there is in a furnace or cupola, the more fuel required to smelt or melt the iron. Alumina is also pronounced in its effects upon the decrease or increase of the fluidity of the slag. As a general thing, the more alumina the higher the temperature required to fuse the flux in order to make a good liquid slag.
The following Table 10 is a compilation of fluxes which the author has used with good results, and will serve to illustrate the physical as well as the chemical properties, and will also show that a flux which, might work well in a furnace can often be well utilized in cupola practice:gases, heated stock, and liquid metal should enable can counteract the absorbing power ofee reactiony they are often composed of about equal parts of silica and alumina. Bricks should contain silica or alumina in proportion to the amount of heat or friction they are                                                 if j