74 SCIENCE IN SHORT CHAPTERS. 



and these oxides at once arrange themselves according to 

 their specific gravities. The oxidized carbon forms atmos- 

 pheric matter and rises above all as carbonic acid, then the 

 oxidized silicon, being lighter than the iron, floats above 

 that, and combines with aluminium or calcium that may 

 have been in the pig and with some of the iron; thus form- 

 ing 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 silicates i.e., the rock matter separate from the me- 

 tallic matter and solidify on the surface as a thin crust, 

 which behaves in a very interesting and instructive manner. 

 At first a mere skin is formed. This gradually thickens, 

 and as it thickens and cools becomes corrugated into moun- 

 tain chaines and valleys much higher and deeper, in pro- 

 portion to the whole mass, than the mountain chains and 

 valleys of our planet. After this crust has thickened to a 

 certain extent volcanic action commences. Eifts, dykes, 

 and faults are formed by the shrinkage of the metal below, 

 and streams of lava are ejected. Here and there these lava 

 streams accumulate around their vent and form insolated 

 conical volcanic mountains with decided craters, from which 

 the eruption continues for some time. These volcanoes are 

 relatively far higher than Chimborazo. The magnitude of 

 these actions varies with the quality of the pig-iron. 



The open hearth finery is now but little used, but prob- 

 ably some are to be seen at work occasionally in the neigh- 

 borhood of Glasgow, and I am sure that Sir William 

 Thomson will find a visit to one of them very intresting. 

 Failing this, he may easily make an experiment by tapping 

 into a good-sized "cinder bogie" some melted pig-iron from 

 a pudding furnace (taking it just before the iron "comes 

 to nature"), and leaving the melted mixture to cool slowly 

 and undisturbed. 



The cinder of the blast furnace, which in like manner 

 floats on the top of the melted pig-iron, resembles still more 

 closely the prevailing rock-matter of the earth, on account 



