Krug von Nidda on the Mineral Springs of Iceland. 109 



of the Geyser contains very little carbonic acid. On the other 

 hand, when it comes from the spring, a gas predominates, which 

 is so feebly united with the water, that it leaves it in a gaseous 

 form, almost at the instant the surface is reached, and so much 

 the more easily, because the springs have a very high tempera- 

 ture. This is sulphuretted hydrogen gas, which is contained 

 in all the Icelandic springs that are distinguished by their high 

 temperature, and by their containing a considerable amount of 

 dissolved silica. Its presence is at once rendered evident by the 

 smell of the ascending vapours. 



It is this gas also, that, united with steam, issues from those 

 openings, which I have termed gas springs, and which arc 

 scattered in great abundance on the declivity of the neighbour- 

 ing small rocky hill. Most of these gas springs, those, namely, 

 which occupy the higher part of the hill, are entirely free of a 

 rising of water ; and only some of the deep-lying openings at the 

 base of the hill contain a small quantity of muddy water. The 

 loose fissured structure of the tuffaceous and slaggy conglome- 

 rate composing the hill, prevents the water from accumulating 

 on its summit or declivity, and causes it to flow to thp deeper 

 points situated at its base. The small quantity water oc- 

 curring in some of the deeper openings seems to be deposited by 

 the moist gases which are constantly evolved. This water is not 

 like the pure transparent water of the Geyser or the Strokr, 

 but is variously tinted by the clay which is mechanically sus- 

 pended in it. The quantity of clay is so great that it forms 

 with the water a pasty moisture, which is constantly kept in an 

 agitated and bubbling condition by the disengagement of the 

 gases. 



Besides the sulphureted hydrogen, the gases evolved consist 

 of sulphurous acid, and perhaps sulphur in the state of vapour. 

 The sulphureted hydrogen by contact with the atmospheric 

 air, and the intervention of watery vapour, undergoes a partial 

 decomposition. The hydrogen unites with the oxygen of the 

 air, and the sulphur is separated. The sulphurous acid, also, 

 exercises an oxydizing power on the sulphureted hydrogen, 

 and then the sulphur of both gases is separated. Finally the 

 sulphur of the gaseous sulphur is condensed. The sulphurous 

 acid by acquiring oxygen is converted into sulphuric acid and 



