Hot and Tnermal Springs. 337 



sary for the evolution of the gas, notwithstanding that the re- 

 ceiver was guarded from the radiated heat by a screen. 



To ascertain the temperature of the gas at the moment of its 

 leaving the gun-barrel, I introduced a very delicate thermome- 

 ter immediately into the stream of gas at the moment of its 

 escape ; it rose, however, only to 88°.25, although the gun-bar- 

 rel, at the end from which the gas issued, had a temperature of 

 144°.5. A repetition of this experiment gave the same result.* 



If, then, we suppose that, at a certain depth in the earth, car- 

 bonic acid gas is generated in a similar manner, by the heating 

 of carbonate of lipie to a red heat, and that it is absorbed at a 

 certain height above this subterranean laboratory by the waters 

 of springs, the temperature of those springs could only be raised 

 about 0°.9. 



Leop. von Buch says farther, that the elevated temperature 

 of acidulous springs is easy to be understood, if we consider for 

 a moment how they make their appearance on the surface. 

 They always owe their existence, namely, to the escape of car- 

 bonic acid, from hot mineral springs strongly impregnated with 

 gas, which exist in clefts or in narrow valleys, at a considerable 

 depth. The carbonic acid expelled by the hot water escapes, 

 making a passage up through the cracks in the rocks, combines 

 with the colder waters with which it meets, and comes to the 

 surface in the shape of acidulous springs, bearing a temperature 

 somewhat above the original temperature of the water. 



In order to make a trial of this hypothesis by means of a few 

 direct experiments, I evolved carbonic acid gas by boiling an 

 acidulous water, which was very rich in carbonic acid, in a re- 

 tort, and introduced a very delicate thermometer into the mouth 

 of the retort, immediately in the stream of gas. The tempe- 

 rature of the mineral water before the experiment was 57°.65, 



• The greater part of the heat which the carbonate of lime receives, seems 

 to be applied in converting the carbonic acid into the gaseous state. It is 

 singular that carbonic acid gas disengaged from chalk by means of concentra- 

 ted sulphuric acid, acquires a much higher temperature than that which is 

 liberated by heat. The temperature of the gas disengaged by sulphuric acid 

 rose to 133^.25, and would, doubtless, have risen still higher, had not the 

 mass, in consequence of the too violent escape of the gas, come into contact 

 with the thermometer. The temperature of the mass itself was much above 



21 2^ 



