82 FLORIDA GEOLOGICAL SURVEY—I5TH 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 con¬ 
tent of such silicates is usually quite low, and they therefore supply but 
little. When lime is present in the form of the carbonate, (CaCOs), 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, (CO 2 ). 
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 1 states that: “If the temperature is raised higher than is re¬ 
quired simply to drive off the carbon dioxide, and if some of the min¬ 
eral particles soften, a chemical reaction begins between the lime, iron, 
and some of the silica and alumina of the clay, the result being the forma¬ 
tion 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 incip¬ 
ient fusion and viscosity by the addition of quartz and feldspar.” 
bRies, H., Clays, Their Occurrence, Properties and Uses, p. 87, 1908. 
