﻿Acetylene. 91 



carbon, and the carbides and not the oxides of the alka- 

 line earths are the stable forms of combination. 



Then, at a lower temperature, the bright red heat of 

 our smelting furnaces, the same carbides formed in the 

 electric furnace, when exposed to free oxygen or to air,, 

 burn to oxides and to carbonic acid, and at a still lower • 

 temperature these two unite to form carbonates repre- 

 sented by the chalk and magnesian limestone which make- 

 so large a part of the earth's crust. Nature has so ad- 

 justed her processes that a small residue of oxygen 

 remains, which, mixed with nitrogen, constitutes the vital 

 air of our atmosphere. The carbides of aluminum and 

 silicon burn in a similar way with oxygen, and the stable- 

 condition at any temperature lower than a bright-red heat, 

 is that of silicates and carbonates which make the chief 

 strata of the earth. 



The oxidation of carbides, which became possible when 

 our globe cooled down to a red heat and solidified, has- 

 perhaps been a superficial one, and the denser material 

 below the crust may consist of carbides of the alkaline 

 earths and carbides of the heavy metals like iron, and 

 finally the metals themselves. 



It is only within the past two years that experiments 

 with the electric furnace have enabled us to study these 

 new transformations at a high temperature, and have- 

 given us the means of estimating w^hat must have been 

 the primitive condition of the earth during long geological, 

 periods. 



Berthelot, Moissan and others have pointed out that 

 the evolution of marsh gas from volcanoes may be an 

 indication of the existence of Plutonic remnants of car- 

 bides, dating from a period of higher temperature, and. 

 which we now know may give ofi' gas when brought in 

 contact with moisture. 



The most important and original experiments made^ 

 with the electric furnace have been published in the 



