52 SCIENCE IN SHORT CHAPTERS. 



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 from this chasm soon becomes local- 

 ized, so as to form a single crater, or a small chain of 

 craters; these gradually develop into cones by the accumla- 

 tion of outflowing lava, so that when the whole mass has 

 solidified, it is covered more or less thickly with a number 

 of such hiUocks, 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 formed. 

 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., towards the centre of the thin upper crust, 

 and thus a single crater and a single cone of the large rela- 

 tive dimensions above described are commonly formed. 



The magnitude and perfection of these miniature volca- 

 noes vary considerably with the quality of the pig-iron and 

 the treatment 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 and oxides of iron, alumina, manga- 

 nese, etc. The cinder separated from this iron displayed the 

 phenomena above described very remarkably, and jets of 

 yellowish flame were thrown up from the craters while the 

 lava was flowing. The flame was succeeded by dense white 

 vapors as the temperature of the cinder lowered, and a 

 deposit of snow-like, flocculent crystals was left upon and 

 around the mouth or crater of each cone. The miniature 

 representation of cosmical eruptions was thus rendered still 

 more striking, even to the whito deposit of the haloid salts 

 which Palmieri has described as remaining after the recent 

 eruption of Vesuvius. 



The gases thus evolved have not yet been analytically 



