662 NEW YOKK STATE MUSEUM 



century that the special application of limestone with a large 

 amount of clay has been recognized. 



The lime made from pnre or nearly pure limestone is some- 

 times called air lime in contradistinction to hydraulic lime made 

 from aluminous or clayey limestones. 



Burning lime. ^ " The time required depends on the density and 

 size of the lumps of stone and also on the moisture content; for 

 water aids to a certain extent in carrying off the carbon dioxid. 

 It is stated that in the presence of steam limestone can be burned 

 in one eighth the time required in dry air and the gases of combus- 

 tion. This accounts for the fact that stone freshly quarried can 

 be burned faster; it has not yet lost its quarry moisture. Period- 

 ical injections of steam or water into the kiln are recommended 

 by some, but are not always necessary in the case of flame kilns.'' 



Limestone which is burned too slowly will make lime of in- 

 ferior quality and will slake more slowly. 



Limestone begins to lose its carbonic acid gas at 750° F, but it 

 does not entirely pass off till the temperature of 1300° or 1400° F 

 is reached. Limestone should never be burned with a coal run- 

 ning high in sulfur, as the latter unites readily with the lime, 

 forming calcium sulfate. This sulfate of lime reacts subsequently 

 with the aid of moisture on any alkalis that may be present, with 

 the formation of alkaline sulfates, which being soluble, are often 

 brought to the surface after the lime is in the wall, forming thus 

 the unsightly white coating that is sometimes seen on bricks. 

 This coating may also be at times caused by the presence of soluble 

 sulfates in the clay. ^■ 



Limekilns. The kilns used for burning lime bear more or less 

 similarity to each other, the general principle of construction 

 being that of a cylindric chamber, lined with fire brick, open at the 

 top and tapering below to a discharge opening. 



Limekilns are either continuous or intermittent in their action. 



In the latter the stone is put into the kiln with alternate layers 

 of fuel till the kiln is full. The fire is lighted, and the mass 



^ Frasch. Min. ind. 7: 483. 



