600 IfEW YOEK STATE MUSEUM 



lithographing 



lithographic limestone is a somewhat impure, very fine and 

 even grained limestone. It is not only rare but valuable. The 

 requirements are sufficient porosity to absorb ink and softness 

 enough to permit working with an engraver's tool. A very great 

 degree of porosity is undesirable. The stone should also be free 

 from cracks, or specks of impurities. 



The chief supply thus far has come from Solenhofen, Bavaria 

 and southern France. It has been j'eported from various local- 

 ities in this country but never from ISTew York state. 



Lime 



When limestone is burned, that is when it is raised to a red 

 heat, it is dissociated into lime oxid and carbonic acid thus. 



CaCOg = CaO + CO^ 



limestone or lime oxid carbonic acid gas 



lime carbonate quick lime carbon dioxid 



caustic .lime 



The carbonic acid gas passes off and the oxid of lime remains 

 behind as a powdery or lumpy substance, which is often white, 

 but may be more or less colored if iron is present. 



As limestone varies in composition, the lime will also, but the 

 percentage of impurities in the lime will be nearly twice what 

 they were in the limestone, for the latter has lost 44;^ of car- 

 bonic acid gas. 



Pure limestone consists of 6Qi of oxid of lime (CaO) and 44;^ 

 of carbonic acid. The change from carbonate of lime to oxid 

 of lime occurs during the burning, the carbonic acid being driven 

 off at a higher temperature, and in this process the lime loses 

 about 44;^ by weight; but, as it is generally in a somewhat moist 

 condition when it is put into the kiln, due to water in its pores, 

 the loss in weight may be still greater than that mentioned above. 

 The percentage of moisture in limestone is very variable and 

 depends largely on the hardness and density of the rock. The 

 denser a limestone the less porous it will be and the lower will 



