342 Prof. Bischof on the Temperature of 



vicinity of the Laacher See and in tlie Eifel. I do not, how- 

 ever, consider this as a sufficient proof, as, in my opinion, all 

 these exhalation s proceed from mineral springs situated below 

 them,* 



If we assume that, fi'om whatsoever cause, water in the inte- 

 rior of the earth is heated to S1S% and that carbonic acid gas 

 of a temperature much above the boiling point be forced at 

 the same time through it ; that water would not only not be- 

 come more heated, but, on the contrary, would suffer a diminu- 

 tion of its temperature, on account of the evaporation. This 

 may, perhaps, be one of the causes that so few of the known 

 hot springs reach the boiling point. 



I support this assertion upon several experiments which I 

 made for that purpose. Thus, on driving air heated to the 

 melting point of tin in such considerable quantities as a large 

 double action bellows was capable of giving, for a whole hour, 

 through about 12 ounces of water of 60°.125, it only caused the 

 temperature of the water to rise to 119^75. Indeed, when the 

 water was surrounded by other water kept continually boiling, 

 the passing of the heated air through it always caused a depres- 

 sion, greater or less, of its temperature ; in one case from 194'' 

 to 158°. The boiling of the surrounding water decreased in 

 violence perceptibly when the heated air was let in to the water, 

 and, ou the other hand, increased, when the stream of hot air 

 was interrupted. 



To all the objections already taken, to the hypothesis that car- 

 bonic acid gas is the cause of the warming of acidulous springs, 

 it may be added, that their temperature does not always exceed 

 that of the fresh- water springs. In April 1833 I found the 

 temperature of the acidulous waters of Meinberg, and of the 

 carbonic acid which is disengaged from them in great quantities 

 and with great violence, to be only 41°.45. Among the obser- 

 vations communicated in Chap. VI. on the temperature of these 

 springs at different seasons, we find that their yearly mean dif- 

 fers but little from that of the neighbouring fresh- water springs. 

 The carbonic acid cannot, therefore, increase their temperature 

 at all, although they contain 0,9 and 1,31 times their volume of 



• Poggend. Ann. vol. xxxii. p. 248. 



