288 THE POPULAR SCIENCE MONTHLY. 



in life, put up Avith being left behind, although we had the first 

 start, and I have no choice left but to resign myself. 



Tlie presence of carbonic acid in the soil and its periodical motion 

 are for the present a bare fact. Other places, with difierent soils, 

 must be examined under varying circumstances, and for longer pe- 

 riods, before an explanation can be attempted. 



The first question which naturally meets us is that about the origin 

 of this gas. It cannot spring from the humus of the surface, because 

 at Munich and Dresden its quantity is smallest in the immediate 

 neighborhood of the surface, where the humus lies, and increases in 

 proportion to the distance thence. As the amount of carbonic 

 acid in the ground-air generally increases the nearer this is to the 

 ground-water, we should be at first sight inclined to assume that it 

 evaporates from it. Is it not a fact that the ground-water which 

 feeds wells and sources contains this gas ? And is it not well known 

 that many a well's shaft contains so much carbonic acid as to extin- 

 guish a burning candle at the distance of a few feet only from its 

 o23ening ? This assumption, however, is not justified for several rea- 

 sons, according to the researches and exjDeriments made at Munich : 

 1. There are two months in the year when the amount contained 

 in the upper stratiim, which is at the greatest distance from the 

 ground-water, is larger than in the lower. 2. I have examined simul- 

 taneously, at given places, the amount of the gas both in the ground- 

 water and in the ground-air, and have investigated whethej-, accord- 

 ing to the laws of diffusion and absorption, either had a suri:)lus of 

 the gas, and was accordingly in a condition to receive or yield some 

 of it. In every case the amount of carbonic acid in the ground-air 

 was larger by fifty per cent, than in the ground-water, so it is clear 

 that it is the water which receives its carbonic acid from the air, and 

 not vice versa. 



Hereby the question about the origin of the gas is certainly not yet 

 answered, and would have been left equally unsettled if we had to 

 ask, Whence comes all the carbonic acid which is found in the ground- 

 water? All this water is precipitated from the atmosphere, from rain 

 or snow. In entering the soil as meteoric water its amount of car- 

 bonic acid is exceedingly small. By help of Bunsen's analytical tables 

 it is easy to calculate, from the quantity of carbonic acid in the at- 

 mosphere, and the absoi-bing power of water for this gas, that one 

 pint of rain-water at the average temperature and barometrical press- 

 ure can only contain a very small fraction of a grain of carbonic acid, 

 and this has been proved further by analytical experience. But the anal- 

 ysis of the pump-water in Munich which was poorest in carbonic acid 

 showed that it contained on an average l|^to \-^ grain of the free gas. 

 The ground-water at the places of examination stands about sixteen 

 feet from the surface. It is therefore evident that the meteoric water, 

 which is the sole source of the ground-water, must more than centuple 



