THE SOLIDITY OF THE EARTH. 123 



The scoria thus formed will float upon the heavy metals below 

 and protect them from cooling by resisting their radiation ; but 

 if in the course of contraction of this crust some fissures are 

 formed reaching to the melted metals below, the pressure of 

 the floating solid will inject the fluid metal upward into these 

 fissures to a height corresponding to the flotation depth of the 

 solid, and thus form metallic veins permeating the lower strata 

 of the crust. I need scarcely add that this would rudely but 

 fairly represent what we know of the earth. 



But it may be objected that I only describe an imaginary 

 experiment. This is true as regards the whole of the materials 

 united in a single fusion. Nobody has yet produced a com- 

 plete model with platinum and gold in the centre, and all the 

 other metals arranged in theoretical order with the oxidized, 

 silicated, and carbonated crust outside ; but with a limited 

 number of elements this has been done, is being done daily, 

 on a scale of sufficient magnitude to amply refute Sir William 

 Thomson's description of a fused earth solidifying from the 

 centre outward. 



This refutation is to be seen in our blast furnaces, refining 

 furnaces, puddling furnaces, Bessemer ladles, steel-melting pots, 

 cupels, foundry crucibles ; in fact, in almost every metallurgical 

 operation down to the simple fusion of lead or solder in a 

 plumber's ladle, with its familiar floating crust of dross or 

 oxide. 



As an example, I will, on account of its simplicity, take 

 the open-hearth refinery and the refining of pig-iron. Here a 

 metallic mixture of iron, silicon, carbon, sulphur, etc. is sim- 

 ply fused and exposed to the superficial action of atmospheric 

 air. What is the result ? 



Oxidation of the more oxidizable constituents takes place, 

 and these oxides at once arrange themselves according to their 

 specific gravities. The oxidized carbon forms atmospheric 

 matter and rises above all as carbonic acid ; then the oxidized 

 silicon, being lighter than the iron, floats above that and com- 

 bines with aluminium or calcium that may have been in the pig 

 and with some of the iron ; thus forming a silicious crust 

 closely resembling the predominating material of the earth's 

 crust. 



When the oxidation in the finery is carried far enough, the 

 melted material is tapped out into a rectangular basin or 

 mould, usually about 10 feet long and about 3 feet wide, 

 where it settles and cools. During this cooling the silica and 



