82 FLORIDA GEOLOGICAL SURVEY-15TH ANNUAL REPORT

 Lime-Lime is found in one form or another in many clays, but all forms may be classed as carbonates, silicates, or sulphates. Calcite, or to a lesser extent dolomite, is the usual source of lime carbonate, gypsum is usually the source of the sulphate. Some silicates such as some of the feldspars and garnet may contain lime in combination, but the lime content of such silicates is usually quite low, and they therefore supply but little. When lime is present in the form of the carbonate, (CaCO3), it may be detected by the application of an acid, as hydrochloric or nitric, which will react with the carbonate to produce an effervescence due to the escape of the carbon dioxide, (C02).
 When in the form of the carbonate, lime is the most effective. If in a finely divided state it acts as a flux. When not in a finely divided state the carbonate changes to quicklime on burning with the loss of the carbon dioxide gas. The quicklime later takes up moisture from the atmosphere and slakes with accompanying swelling or crumbling.
 Ries' states that: "If the temperature is raised higher than is required simply to drive off the carbon dioxide, and if some of the mineral particles soften, a chemical reaction begins between the lime, iron, and some of the silica and alumina of the clay, the result being the formation within the clay of a new silicate of very complex composition. The effects of this combination are several: In the first place the lime tends to destroy the red coloring of the iron and imparts instead a buff color to the burned clay. This bleaching action is most marked when the percentage of lime is three times that of iron. It should be remembered, however, that all buff-burning clays are not calcareous, and that a clay containing a low percentage of iron oxide may also give a buff body. Another effect of lime, if present in sufficient quantity, is to cause the clay to soften rapidly, thereby sometimes drawing the points of incipient fusion and viscosity close together and giving what is termed a short firing range.
 This rapid softening of the calcareous clays is one of the main objections to their use, and on this account also it is not usually safe to attempt the manufacture of vitrified products from them, but the presence of several per cent of magnesia will counteract this. It has also been found possible to increase the interval between the points of incipient fusion and viscosity by the addition of quartz and feldspar."
 'Ries, H., Clays, Their Occurrence, Properties and Uses, p. 87, 1908.