27-6 



VOLCANIC PRODUCTS. 



to issue through the cracks, and the ground was covered with a yel- 

 low and black powder : thus, a subterraneous fire was produced by 

 the chemical combination of sulphur, iron, and water. In the cliffs 

 of Charmouth, Whitby and Weymouth, we have precisely the same 

 mineral substances combined, that were used in the experiment of 

 Lemery. 



The earth itself is, in all probability, the great laboratory in which, 

 by the aid of subterranean heat, are combined and prepared the min- 

 eral substances that compose the hard crystalline crust of the globe. 

 All the minerals which form primary rocks, occur in a perfect state, 

 in modern or ancient lava. The substances ejected through fissures 

 in the earth, or volcanoes, belong to the four grand divisions of the 

 mineral kingdom, — the inflammable, saline, metallic, and earthy. 



The inflammable substances are sulphur, carbon, and hydrogen. 

 The inflammable quality of sulphur prevents its being found in lava 

 in a solid form ; during volcanic eruptions it is evolved in a gaseous 

 state combined with hydrogen. It is also sublimed from the fissures 

 of extinct or dormant volcanoes, and forms thick incrustations on the 

 sides of the craters. Almost all the sulphur of commerce in Europe 

 is procured from the craters of dormant volcanoes in the south of 

 Italy, Sicily, and the Lipari Islands. When the combustion of sul- 

 phur in volcanoes takes place where there is access to atmospheric 

 air, it forms sulphurous acid gas, and sulphuric acid. 



Carbon combined with hydrogen, forming bitumen, is found in 

 volcanic rocks, and also in some basaltic or trap rocks. The volca- 

 nic tufa in the vicinity of Clermont, in France, contains so much 

 bitumen, that in warm days it oozes out, and forms streams of bitu- 

 men resembling pitch, which is the more remarkable, as this tufa 

 must have been erupted some thousand years. Bitumen has been 

 observed oozing out of the lava of ^ma. The raoya ejected from 

 the volcanoes in the Andes, in aqueous or muddy eruptions, contains 

 so much bitumen or carbon, as to be inflammable. As bitumen ex- 

 ists in many volcanic rocks, the black smoke which issues during an 

 eruption may proceed from its combustion, though it has generally) 

 been supposed to consist of minute volcanic sand, called ashes. 

 Carbon also combines with hydrogen in a gaseous state, and forms 

 carburreted hydrogen gas. 



The hydrogen gas evolved from volcanoes, or from chasms in the 

 earth during earthquakes, is generally combined with sulphur or car- 

 bon ; it is probably formed by the decomposition of water, when it 

 finds access to subterranean fire. Whether phosphorus be a pro- 

 duct of volcanoes is unknown : its extreme inflammability prevents 

 it from being discovered in a concrete form ; but the dense white 

 clouds, like bales of cotton, which sometimes cover Vesuvius, resem- 

 ble the fumes produced by the combustion of phosphorus. Among 

 the products of volcanoes, only thtee are combustible at a moderate 

 temperature ; — sulphur, hydrogen, and carbon. It has been eonjec- 



