M. R. Buuseu on the Law of Absorption of Gases. 199 



From this table it is plainly seen, that if the gas passing 

 through a spring at 15°'l contains only 10 per cent, of carbonic 

 acid with 90 per cent, of nitrogen, the gas dissolved in the 

 spring water will contain 42-948 per cent, of carbonic acid. In 

 this way it is easy, in analyses of mineral waters, to calculate 

 the composition of the gases contained in the water, if the com- 

 position of the gas which is set free in the spring is known by 

 experiment. If the composition of both gases is directly deter- 

 mined, and the experimental composition agrees with that found 

 by calculation, we have a most valuable confirmation of the cor- 

 rectness of both analyses. 



All these deductions from the law of absorption are of course 

 only applicable to cases in which a statical equilibrium between 

 the free and dissolved gases can ensue. This is not only the 

 case in springs through which gases pass, but particularly in rain 

 and dew, and for these is the law applicable with its greatest 

 precision. 



The amount of carbonic acid contained in the air varies, ac- 

 cording to Saussure's numerous experiments, in 10,000 parts of 

 air between 5'74 and 3-15, giving a mean of 4-15. According 

 to this mean value the air is composed of — 



Oxygen 209512 



Nitrogen 79-0073 



Carbonic acid . . . 0-0415 

 1000000 

 From this analysis, by means of equations (7) and (8), we obtain 

 the following table, representing the mean constitution of the 

 gases contained in rain water for the temperatures given in the 

 upper line. 



It is directly seen from this table that the amount of carbonic 

 acid which the plants receive from the rain decreases for increa- 

 sing temperatures. 



The mean yearly amount of rain which falls on the surface 

 of the earth is, according to Eerghaus, equal to a layer of 

 water of only l m, 5 in height. By the help of formula (3) it is ■ 

 found, that with this stratum of water a volume of carbonic acid 

 is conveyed to the earth which lias a height of only 1-293 mil- 

 limetre at 0° and 0'7G pressure; this gives for every square 



