R
 A PRELIMINARY REPORT ON CLAYS OF FLORIDA k

 clay. Indeed, sand is often added to some brick clays having a hijh shrinkage in order to reduce the shrinkage.
 Contrary to the belief of some, the addition of quartz does not raise the fusion point of a clay. Quartz alone is very refractory, but in te presence of highly aluminous low-flux clays its refractoriness is Reduced. A high percentage of silica for a very refractory clay is >t desirable.
 Alumina-Alumina is one of the common constituents of all clays and is derived not only from kaolinite but many of the other silicates Is well. Alone it is highly refractory, but in the presence of fluxes its fusion point is lowered.
 Iron Oxide-This includes both the ferric Qxide, Fe2Oi, and tfie ferrous oxide, FeO. The iron oxides in clay are derived from such iron minerals as limonite, hematite, pyrite, siderite, and also from sul silicates as mica, hornblende, garnet, glauconite, etc.
 Iron acts as a strong coloring agent in both the burned and unburned clay. Its range of color influence is from a very faint creaiBi, through yellow and buff, to all shades of red, brown, and blue to bla&. The resulting color, however, is not solely determined by the quantify of iron oxide present but also by the texture and distribution in the cla the form of the iron, whether ferric or ferrous, condition of the kifh atmosphere, whether oxidizing or reducing, and the neutralization effdt of other constituents as lime.
 The iron oxides likewise exert a strong fluxing action, thus lowe ing the fusion point of the clay. Ries1 states that "this effect will e more pronounced if the iron is in a ferrous condition or if silica s present." The iron oxide probably enters into combination with silica, forming an easily fusible silicate. 1
 Iron may therefore be either a desirable or an undesirable ingredient of. clays. In the lower grades of ware its coloring and fluxing action is beneficial. The fluxing action reduces the temperature at which burning must be done. In other wares, such as white wares and refractory prodI
ucts, it is detrimental. It is obvious that in white-burning clays the iron content must be very low. Q



 'Ries, H., Clays, Their Occurrence, Properties and Uses, p. 85, 1908.