104 SCIENCE IN SHORT CHAPTERS. 



violent to eject small spurts of molten cinder to a height equal 

 to four. or live diameters of the whole mass. 



The crust once broken, a regular crater is rapidly formed, 

 and miniature streams of lava continue to pour from it ; some- 

 times slowJy and regularly, occasionally with jerks and spurts 

 due to the bursting of bubbles of gas. The accumulation of 

 these lava-streams forms a regular cone, the height of which 

 goes on increasing. I have seen a bogie about 10 or 12 inches 

 in diameter, and 9 or 10 inches deep, thus surmounted by a 

 cone above 5 inches high, with a base equal to the whole diam- 

 eter of the bogie. These cones and craters could be but little 

 improved by a modeller desiring to represent a typical volcano 

 in miniature. 



Similar craters and cones are formed on the surface of cinder 

 which is not confined by the sides of the bogie. I have seen 

 them well displayed on the " running-out beds" of refinery 

 furnaces. These, when filled, form a small lake of molten iron 

 covered with a layer of cinder. This cinder first skins over, as in 

 the bogies, then small crevasses form in this crust, and through 

 these the fused cinder oozes from below. The outflow 7 from 

 this chasm soon becomes localized, so as to form a single crater, 

 or a small chain of craters ; these gradually develop into cones 

 by the accumulation of outflowing lava, so that when the whole 

 mass has solidified, it is covered more or less thickly with a 

 number of such hillocks. These, however, are much smaller 

 than in the former case, reaching to only one or two inches in 

 height, with a proportionate base. It is evident that the 

 dimensions of these miniature volcanoes are determined mainly 

 by the depth of the molten matter from which they are foimed. 

 In the case of the bogies, they are exaggerated by the over- 

 powering resistance of the solid iron bottom and sides, which 

 force all the exudation in the one direction of least resistance 

 viz. toward the centre of the thin upper crust, and thus a 

 single crater and a single cone of the large relative dimensions 

 above described are commonly formed. 



The magnitude and perfection of these miniature volcanoes 

 .vary considerably with the quality of the pig-iron and the treat- 

 ment it has received, and the difference appears to depend 

 upon the evolution of gases, such as carbonic oxide, volatile 

 chlorides, fluorides, etc. I mention the fluorides particularly, 

 having been recently engaged in making some experiments on 

 Mr. Henderson's process for refining pig-iron, by exposing it 

 when fused to the action of a mixture of fluoride of calcium 



