REPORT ON MINKRAL AND THKRMAL WATERS. 27 



the truth of the remark, that Bteam under high pressure be- 

 comes a rapid solvent of alkaline silicates. 



The latter chemist even found*, that glass exposed to the va- 

 po\ir issuing from an high-pressure engine was rapidly corroded, 

 and that the silica taken up was again deposited in a beautiful 

 stalactitical form. 



It however remains open to further inquiry — How far 



1st, What is the solvent of silica in springs which contain no unaccount- 

 free alkali : ^^ for. 



2nd, By what means it is held in solution by the sap of ve- 

 getables : 



3rd, What are the circumstances which interfere with its 

 solution by artificial means. 



With reference to this subject, I may allude to an interesting 

 memoir by Professor Fuchs, on the amorphism of solid bodiesf , 

 as throwing some light upon the question as to the solubility of 

 silex, and illustrating the influence in this case of mechanical 

 obstacles upon chemical affinities. 



He has shown, that silica exists in minerals in two condi- 

 tions, a crystallized and an amorphous one, and that in the 

 latter it is much more readily acted upon by solvents, than in 

 the former;}:. 



Dr. Turner also found, that whilst glass was rapidly dissolved 

 by high-pressure steam, rock crystal remained unchanged. 



It would have been curious to determine, whether under such 

 circumstances, amorphous silex (such as opal) would continue 

 untouched. 



Muriatic and sulphuric acids in a free state are found only in Muriatic 

 spi'ings connected with volcanos, to which they are obviously and Sul- 

 riferable. f^^'^ 



Boracic acid, which has been detected in a thermal spring of Boracic 

 the island of Ischia, and more abundantly in the water of the A"d. 

 Lagoni of Tuscany, seems also to be a volcanic product. 



It is well known as resulting from volcanic operations in the 

 Lipari Islands and elsewhere ; and its appearance in their craters 



• Proceedings of the Geol. Soc, vol. ii. p. 95. 



t Edinh. New PJii^os. Juiirnal for April, 1835. 



J A recent traveller in Iceland (Kriig von Nidda) in Karsten's^rcAti', vol.ix., 

 remarks, " tliat the solubility of the silica in such considerable quantity in 

 the hot springs of Iceland, remained for a long time a puzzling phaenome- 

 non, until that property was discovered, which it has in common with 

 phosphoric acid, viz. of forming two isomeric modifications, of which one is 

 insoluble in water and in acids ; the other is soluble in both." This may 

 be ti-ue ; but the statement must be regarded as a mere expression of a fact, 

 not as the explanation of it. 



