372 



the water, and this substance must moreover be present in, 

 practically, infinite quantities, because it would otherwise very 

 soon be saturated with carbonic acid at the tension of the 

 atmosphere. 



Such a substance is found in the rocks above and through 

 which the water flows and the particles of which it holds in 

 suspension. Almost the whole of Disko is basaltic M, and the 

 carbonic acid, as the stronger of the two, tends to replace the 

 silicic acid in its salts. In this particular instance the basalt 

 is decomposed by the formation of carbonate of lime and free 

 sihcic acid. 



The phenomenon has been investigated by Bischof (Lehr- 

 buch der ehem. und phys. Geologie, Bd. I, 2. ed. Bonn 1863) 

 who has made several very convincing experiments. 



If for instance a stream of carbonic acid is conducted 

 through a solution of silicate of potassium or sodium a con- 

 siderable quantity of carbonate is formed, but the decomposition 

 of the silicate never becomes complete. A state of equilibrium 

 will be attained in which acid silicates as well as carbonates 

 are present (p. 31). 



Sihcate of lime, suspended in water, is very readily decom- 

 posed by a stream of carbonic acid, and a precipitate consisting 

 of CaCOg and free silicic acid is formed (p. 36). 



Silicate of magnesia on the other hand is not in the least 

 affected by carbonic acid (p. 37). 



In perfect accordance with the experiments Bischof found 

 that basaltic rocks, of which silicate of lime forms the chief 

 constituent, very often show effervescence of carbonic acid when 

 treated with dilute muriatic acid. This effervescence is an 

 important sign of the decay of the rocks, and it is sometimes 



^) On the southern and eastern coast of Disko gneiss and sedimentary 

 rocks with coal-beds are found. I have only examined waters from 

 the basalt. 



