SULPHUR OF THE SOLFATARAS. 81 



hurl up the boiling-hot mud often to a height of some 

 fifteen feet, and heap it up into a crater-like wall 

 round the basin of the spring. All these features of 

 the landscape taken as a whole, present a picture of 

 the wildest desolation, set as it is in a frame of 

 the gloomiest rock-land, which surrounds the desert 

 scene, and increases the depth of the dreariness. 



Since the sulphuretted hydrogen only appears 

 mixed in small amount with the carbonic acid 

 and steam, there is reason to believe that it is 

 formed by the passage of the water-vapour, and 

 carbonic acid gas, over sulphuretted metals, such 

 as the sulphides of calcium, potassium and sodium. 

 The sulphurous acid, wherever it does come up, 

 arises, doubtless, from the burning of sulphuretted 

 hydrogen, or of sulphur previously uncombined. 

 The sulphurous acid and sulphuretted hydrogen, 

 being brought into contact by the aid of water, 

 are changed by mutual decomposition into water 

 and sulphur; and thus these gases, when they 

 come forth together from the fumeroles, are always 

 accompanied by sulphur. But the sulphuretted 

 hydrogen gas mixed with steam, also suffers a slow 

 decomposition, by the presence of air, whereby its 

 hydrogen is oxidised into water, and its sulphur is 

 set free. This then at once explains the gradual 

 spread of sulphur over the solfataras. 



The wide distribution of these discharges of 

 carbonic acid gives us reason to conclude that they 



G 



