THE VOLCANIC BOCKS OF ICELAND. 



73 



Since the sulphates as such are not capable of sublimation, it 

 must be assumed that this saline incrustation was originally 

 volatilized in the form of chlorine compounds, which were sub- 

 sequently converted into sulphates by means of sulphurous acid 

 in the presence of aqueous vapour and atmospheric air. In the 

 fumaroles of the lower lava streams, on the contrary, characterized 

 by only a small per-centage of sulphurous acid, the chlorine 

 compounds again predominate, as is shown by the following 

 analyses of products collected there a few months after the last 

 eruption : — 



Chloride of ammonium 

 4Fe2 03 + Fe2CP . . 

 4AP03-fAPCF . . 

 Chloride of magnesium 

 Chloride of calcium . 

 Chloride of sodium 

 Chloride of potassium 



Silica 



Water and stony residue 



99-00 



100-00 



The mode in which this mixture of salts was formed is the 

 same as that of the crater products just treated of, except that 

 in this instance it was not the atmospheric air alone which yielded 

 the ammonia on the formation of chloride of ammonium, but, as 

 I have shown* in another paper, likewise the vegetation t par- 

 tially covering the ground overflowed by lava. 



With regard to the origin of the hydrochloric acid in the crater 

 gases there can be no doubt. Chloride of sodium, which occurs 

 so frequently as a sublimate in volcanoes, is decomposed at very 

 high temperatures, in the presence of aqueous vapours, by silicates 

 into that acid and soda, which unites with the silicates causing 

 the decomposition. It is not necessary to assume that the 

 chlorine compound suffers this decomposition apart from the lava. 



* Liebig's Annalen, vol. Ixv. p. 70. 



t According to my experiments, a square metre of meadow land yields on 

 dry distillation a quantity of ammonia corresponding to 223*3 grms. of chloride 

 of ammonium. 



