28 



THE CUBA REVIEW 



The third class of rock is of fossiUferous origin and this likewise must be sorted before it 

 is prepared for the kiln. 



One of the most troublesome impurties found in lime when used in the clarifieation of cane 

 juices is magnesium due to the fact that this substance collects as a heavy coat on the evapora- 

 tor tubes and imparts the transmission of heat to the boiling juices. Dr. Geerligs gives the 

 maximum content of this material in lime when used in clarifying juices as 2%. Another 

 troublesome impurity is iron. This, however, does not usually occur in large quantities and the 

 presence of even a small amount may easily be detected by the brown color which it imparts 

 to the rock. 



Plate X. — Small 



lime kiln at the Mindoro Sugar Factory, 

 San Jose, Mindoro, P. I. 



The method followed in burning the lime rock determines to a great extent the grade of 

 the finished product. If the heat is not applied evenly throughout the kiln there will be por- 

 tions of the rock left unburned while other portions are overburned. This results in a very 

 unsatisfactory product as well as an extra burden of exjiense due to the loss of heat units. It is 

 important, therefore, that as low a temperature as possible be employed to decompose the lime 

 and convert it into the oxide form, and this must be properly distributed throughout the rock. 

 The temperature may be as low as 700° C. where the gas is immediately removed but where 

 a pressure of the gas is maintained above the burning lime as in the case where the gas is used 

 in the sugar factory, the carbon dioxide and quicklime recombine forming calcium carbonate. 

 For this reason a higher temperature is required in such cases. ^ ' -- 



After the class of fuel to be used in burning the lime has been elected, it is necessary to 

 conduct some experiments with this material and with the particular lime rock employed in 

 order to determine the right proportions of fuel and lime to be used in filling the kiln, i "N^liethe'r 

 w^eighing or measuring methods are employed the charges of lime and fuel should be admitted 

 alternately in order to have them properly mixed. 



