Royal Institution. 153 



exist amicably together. In Iceland they wage incessant war, mutu- 

 ally decompose each other, and scatter their sulphur over the steaming 

 fields. In this way the true solfataras of the island are formed. 



In process of time, however, the heat retires to greater depths, 

 the sources of the sulphurous acid and sulphuretted hydrogen become 

 by degrees exhausted, and at such places the acid reaction of the 

 soil disappears. Carbonic acid is found in abundance everywhere, 

 but as long as the more powerful sulphuric acid is present the former 

 must remain free. But when the acid reaction has disappeared, the 

 carbonic acid combines with the alkaline bases, the bicarbonates 

 thus formed impregnate the thermal waters, and become solvents 

 for the silica which these waters are known to contain in such sur- 

 prising abundance, and which, as we shall presently see, furnishes 

 the materials for the wonderful architecture of the Geisers. 



Casting our thoughts back upon the foregoing description, .the 

 hypothesis of internal heat will be seen to be implied, and from this 

 as a cause we have deduced the various chemical phenomena as con- 

 sequences. Holding fast by experiment, we see that the various 

 gases whose existence has been urged as one of the strongest proofs 

 of the so-called chemical theory, follow in the most natural and 

 necessary manner from the rival supposition. Given the heat and 

 the materials the results are such as any chemist acquainted with 

 the reactions might predict d, priori. By the labours of a chemist 

 indeed a new and wonderful light has been thrown upon the entire 

 volcanic phenomena of Iceland. With implicit reliance on the appli- 

 cability of his science to the solution of these phenomena, he has 

 travelled side by side with nature, combined her conditions, and pro- 

 duced her effects. Basing all his reasoning upon experiment, he 

 has given to his conclusions a stability which mere speculation, 

 however plausible, could never claim. That chemist is Bunsen, to 

 whose researches in Iceland the audience were indebted for the ma- 

 terials of the present discourse. 



The Lecturer then adverted to the Geisers ; and proposed, as his 

 time was limited, to confine his attention to the Great Geiser. We 

 have here a tube ten feet wide and seventy feet deep ; it expands at 

 its summit into a basin, which from north to south measures fifty-two 

 feet across, and in the perpendicular direction sixty feet. The interior 

 of the tube and basin is coated with a beautiful smooth plaster, so 

 hard as to resist the blows of a hammer. The first question that 

 presents itself is, how was this wonderful tube constructed ? How 

 was this perfect plaster laid on ? A glance at the constitution of 

 the Geiser water will perhaps furnish the first surmise. In 1000 

 parts of the water the following constituents are found : — 



Silica 0-5097 



Carbonate of soda .... 0*1939 

 Carbonate of ammonia . . 0*0083 

 Sulphate of soda .... 0*1070 

 Sulphate of potash . . . 0*0475 

 Sulphate of magnesia . . . 0*0042 

 Chloride of sodium . . . 0*2521 

 Sulphide of sodium . . . 0*0088 

 Carbonic acid 0*0557 



