78 FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT

 Hydromica, as the results of the same investigator show, either practically disappears at 1150* C. or loses the greater part of its interference color. Somers states that: "This change of the hydromica on heating suggests that it furnishes some of the flux for the clay, and other things being equal, there may be a connection between the degree of density at the temperature mentioned and the quantity of hydromica present."
 Somers further states that: "If it is not fluxed, kaolinite appears to retain its shape and at least a part of its original interference color. Tourmaline and probably epidote disappear even at 11500 C., but rutile, zircon, and probably titanite seem to be unaffected even at 13000 C."
 A white Florida clay fired at 11500. C. exhibited the formation of sillimanite. Somers believed it to have formed from large flakes of kaolinite or the low-grade hydromica. Other similar clays treated in the same manner did not develop sillimanite.

 THE CHEMICAL ANALYSIS OF CLAYS
 There are in common usage two methods of clay analysis. One of these ig known as the ultimate analysis and the other as the rational analysis.
 The ultimate analysis is the one most frequently used. It is the one which considers the various ingredients of a clay as oxides, yet their exact condition may be in much more complex forms. Calcium carbonate (CaCO3) is thus considered as being broken up into carbon dioxide (C02) and lime (CaO), with the percentage of each given separately. The sum of these two percentages would, on the other hand, be equal to the amount of calcium carbonate in the clay. The common method of expressing the ultimate analysis of a clay is as follows:

 Silica ........................ (SiO 2)
 Alumina ..................... (A203)
 Ferric Oxide ................. (Fe203)
 Ferrous Oxide ................ (FeO)
 Lime ........................ (CaO ). F.
 Magnesia .................... (MgO) Fluxing Impurities.
 Potash ....................... (K20) .Alkai
 Soda ......................... (Na20) A ales
 Titanic acid .................. (TiO 2)
 Sulphur trioxide .............. (SO3)
 Carbon dioxide ............... (C02)
 W ater ....................... (H20 )
 Organic matter ............... ........