76 BUNSEN ON THE FORMATION OF 



84. 



Carbonic acid .... 88*24 



Sulphuretted hydrogen . 6*97 



Hydrogen 4*10 



Nitrogen 0*69 



Carbonic oxide .... 0*00 



Carburetted hydrogen . . 0*00 



100-00 



' About a quarter of an hour's walk from this place, at the spot 

 where in coming from Reykjavik the first large exhalation of 

 vapour occurs in the bottom of the valley itself, there are at the 

 edge of a piece of meadow ground, generally used by travellers 

 for pitching their tents, a number of large pools of boiling mud, 

 between which vapour is observed to break out with remarkable 

 violence. Although the small space of solid ground then sur- 

 rounding it was continually covered with hot clouds of vapour, 

 it was possible to penetrate to the opening from which the va- 

 pour issued by means of the crusts of gypsum which had been 

 formed between the boiling pools, and to collect the gas for 

 analysis with an appropriate apparatus. Its composition was — 



85. 



Nitrogen 0*50 



Carbonic acid .... 79*07 



Sulphuretted hydrogen . 15*71 



Hydrogen 4*72 



Carbonic oxide .... 0*00 



Carburetted hydrogen . . 0*00 



loo-oo 



The enormous force with which these gases accompanied by 

 masses of steam issue, would make it appear that these springs 

 are the principal openings of the fissures and channels from out 

 of which the fumarole gases are diffused through the surround- 

 ing rock, causing its metamorphism. As the dissolved products 

 of this metamorphosis possess, as a predominating character, an 

 acid reaction owing to the formation of sulphuric acid, no traces 

 of carbonate of lime or of silica present themselves among the 

 products of the decomposition of the rocks in which the solfa- 

 taras occur. Since the carbonic acid takes no part in these de- 



