M. R. Bunsen on the Law of Absorption of Gases. 197 



but a small quantity of dissolved salts, there are some whose 

 absorption-coefficients differ but slightly from those of pure 

 water, and contain carbonic acid gas alone in solution. If such 

 springs, as is usually the case, are saturated with gas, a certain 

 limit for the amount of contained carbonic acid may be found. 

 This limit of the quantity of carbonic acid depends upon, — 1st, 

 the temperature of the spring; 2nd, the depth of the shaft of 

 the spring ; 3rd, the height of the spring above the sea. Springs 

 of the above sort, which are saturated with a stream of chemi- 

 cally pure carbonic acid, and rise without pressure at the level 

 of the sea, give according to their temperature very different 

 amounts of gas. They contain in one litre of water the follow- 

 ing amounts of gas for the corresponding temperatures : — 



Cubic centimetres of gas in 



C. 1 litre of water. 



1796-7 



5 1449-7 



10 1184-7 



15 10020 



20 901-4 



If the same spring under otherwise similar circumstances rose 

 at an elevation above the sea, where the average atmospheric 

 pressure was only two-thirds of the mean height of the barome- 

 tric column, it would contain only two-thirds of the above 

 amount of dissolved carbonic acid. 



Hence it will be perceived that the amount of gas in a spring 

 which is saturated with pure carbonic acid, may be considerably 

 augmented by deepening the spring shaft, and thus increasing 

 the column of water under which the gas issues from the earth, 

 as Bischoff has indeed already shown in his admirable researches 

 on the phenomena of springs. If, for example, the depth of 

 the shaft from the surface of the spring to the ground is 15 

 feet, the water where it bubbles out from the earth will contain 

 one-third more carbonic acid than the above amounts show. 

 The water in rising to the surface loses a part of the dissolved 

 gas in proportion as the pressure diminishes, but the statical 

 equilibrium which ensues in consequence of the'law of absorp- 

 tion requires a certain time for its restoration. Thus the Peters 

 spring in Petcrsthal in the Schwarzwald, which has a tempera- 

 ture of 10° C, contains at the surface of the spring, under a 

 pressure m, 735, 12704 cubic centimetres of carbonic acid in 

 the litre, whereas, according to the absorption-coefficient of car- 

 bonic acid for 10 o, 3, it should only contain 1133-3 cubic centi- 

 metres under the same pressure. The water is therefore ovcr- 

 Baturatcd with carbonic acid. This excess of gas is seen to 



