52 STUDIES, SCIENTIFIC AND SOCIAL 



gases to an amount proportioned to the pressure they are 

 under, and with the fact that molten substances do actually 

 absorb large quantities of gases. He says : — 



" Silver in a state of fusion is able to absorb 22 times its volume 

 of oxygen gas. When the metal is allowed to cool this gas is given 

 off, and if the cooling takes place suddenly a crust is formed on the 

 surface, and the phenomenon known as the spitting of silver is 

 exhibited. Sometimes during this operation miniature cones and 

 lava-streams are formed on the surface of the cooling mass, which 

 present a striking resemblance to those formed on a grand scale on 

 the surface of the globe. The researches of Troost and others have 

 shown that molten iron and steel possess the property of absorbing 

 considerable quantities of oxygen, hydrogen, carbonic acid, and 

 carbonic oxide, and that these gases are given off when either the 

 temperature or the pressure is diminished. . . . Von Hochstetter 

 has shown that when molten sulphur is exposed to a temperature 

 of 262° Fahrenheit, and a pressure of two or three atmospheres, in 

 the presence of steam, it is found that the sulphur absorbs a con- 

 siderable quantity of water, which is given off again Avith great 

 violence from the mass as it undergoes solidification. The hardened 

 crust which forms on the surface of the sulphur is agitated and 

 fissured, miniature cones and lava-streams being formed upon it, 

 which have a striking resemblance to the grander phenomena of the 

 same kind exhibited upon the crust of the globe." 



He then goes on to show that the enormous quantity 

 of steam and other gases given off during volcanic action 

 and from flowing lava-streams, can only be accounted for 

 by supposing that the molten rock from which they are 

 derived contains these gases to an amount equal to many 

 times their volume ; and that the same fact is indicated 

 by the liquefied gases that are found in the cavities of 

 the crystals of volcanic products which have consolidated 

 under great pressure, such as granites, porphyries, and 

 other rocks of allied nature. 



There can, therefore, be no doubt as to the fact of the 

 liquid substratum containing in its substance an enormous 

 quantity of gases, the principal being water- vapour, but 

 how the gases came there is less certain; nor does it 

 materially concern us. Some think that these gases have 

 been largely derived from sea-water, which has found its 

 way by percolation to the heated interior ; but there are 



1 Internationcd Scientific Series, vol. xxxv., "Volcanoes," p. 355, 



