THE VOLCANIC ROCKS OP ICELAND. 75 



The gases which penetrate forcibly through the muddy soil of 

 the solfatara fields, or break through the more solid rock in vio- 

 lent streams of vapour, must in this case likewise form the start- 

 ing-point of the investigation. The solfataras of Krisuvik present 

 the most considerable of all the gaseous eruptions of this kind. 

 That jet of vapour, which issues from the loose strong ground 

 of the upper ridge some few hundred feet above the principal 

 group of springs in the valley, pours forth with a hissing noise 

 an immense stream of vapour, the tension of which is sufficient 

 to project stones the size of the hand to a height of several feet. 

 This stream of vapour contains 82*30 steam and 17'20 of gas, 

 having the following composition : — 



82. 



Carbonic acid 87*43 



Sulphuretted hydrogen . . 6*60 



Hydrogen 4*30 



Nitrogen 1-67 



Carbonic oxide .... 0*00 



Carburetted hydrogen . . 0*00 



190-00 

 The composition of this vapour as it issues is — 



83. 



Aqueous vapour .... 82*30 



Carbonic acid 15*47 



Sulphuretted hydrogen . 1*17 



Hydrogen 0*76 



Nitrogen ...... 0*30 



100*00 



According to a measurement, which however must only be 

 regarded as in the highest degree approximative, this spring 

 alone yields, during twenty-four hours, 223 cubic metres of sul- 

 phuretted hydrogen, 12 cubic metres of pure hydrogen, and a 

 quantity of steam, the total effect of which is equal to the power 

 of thirty horses. 



Close to this spring there is another, scarcely inferior in mag- 

 nitude, and exhaling gas, having almost exactly the same com- 

 position as the last, namely, — 



