48 FIELD, FOREST AND FARM 



"A lime-kiln is about three meters high, and is 

 lined with fire-proof brick. An opening at the bot- 

 tom serves for taking out the lime when the firing 

 has continued long enough. In filling the kiln it is 

 the usual practice to begin by laying large pieces of 

 limestone so as to form a sort of rude vault over the 

 fireplace, and on this vault are piled smaller frag- 

 ments until the entire cavity is filled. The fuel used 

 may be fagots, brushwood, turf, or coal. After the 

 firing has gone on long enough, operations are sus- 

 pended and the lime is withdrawn by breaking down 

 the vault supporting the entire mass, which crumbles 

 and comes crowding out at the lower opening, whence 

 it is usually removed. 



"Another method still followed in some localities 

 and of more ancient origin consists of filling the kiln 

 with alternate layers of fuel and limestone. The 

 whole rests on a bed of fagots that serves for starting 

 the fire. As soon as the fire has spread throughout 

 the mass, the opening at the top is closed with pieces 

 of sod in order to make the combustion slower and 

 more even. ' ' 



"Nothing could be simpler," said Jules, "than 

 lime-making. Now I should like to know what effect 

 the heat of the kiln has on the limestone. How does 

 it happen that stone turns into lime by passing 

 through fire?" 



"Limestone," answered his uncle, "contains two 

 different substances : first, lime, and then an invisible 

 substance, impalpable as air itself, in fact, a gas, 

 carbonic acid gas. The name of carbonate of lime 



