82 BUNSEN ON THE FORMATION OP 



Purified Coal-gas from an English Gas-work. 



100. 



Nitrogen 1*89 



Oxygen 0*00 



Carbonic acid 2-83 



Sulphuretted hydrogen . . . trace 



Marsh gas 2691 



Hydrogen 3513 



Carbonic oxide 5*11 



Elayle gas 2-70 



Ditetryle gas 2-28 



100-00 



These analyses, to which I could add a great number of others, 

 sufficiently show that the volcanic gases are characterized by 

 the absence of all combustible carbonaceous substances, while 

 in the gaseous products of dry distillation, or spontaneous de- 

 composition of organic remains, they are scarcely ever wanting. 



If, in accordance with these facts, the solfatara gases can in 

 no way be of organic origin, still it does not require any special 

 hypothesis to account for their formation. The most simple 

 experiment shows that when sulphur and aqueous vapour come 

 into contact with heated pyroxenic rocks, all the conditions 

 necessary for their formation are present. When the vapour of 

 sulphur is passed over basalt, or any other of the pyroxenic 

 rocks treated of above, at a red heat, a partial decomposition of 

 the peroxide of iron in these rocks takes place, the sulphur being 

 divided between its constituents. The oxygen of the oxide 

 escapes in the form of sulphurous acid, and the metal remains in 

 the rock as sulphuret. If afterwards steam is passed over the 

 sulphuretted rock, still at a red heat, an abundance of sulphu- 

 retted hydrogen is disengaged, and magnetic oxide of iron is 

 formed. If the temperature exceeds only very slightly a red 

 heat, a part of this sulphuretted hydrogen is decomposed into 

 its elements, and a sensible quantity of free hydrogen is found 

 mixed with the sulphur vapour. Fragments of basalt, from the 

 Stempelskopf near Marburg, heated to redness in sulphuretted 

 hydrogen, and then treated with steam at a higher temperature, 

 yielded a mixture of gases having the following composition : — 



