Till' Afiiioxjjfiere of flu Soil 



The total amount of gas given up is not great; its characteristic 

 feature is the absence of oxygen (except in small quantities) and the 

 high proportion of carbon dioxide. 



Some of the samples obtained had the composition shown in Table III. 



Table III. Composilion of gas held absorbed by soil. 

 Percentage by volume. 



Pasture soil 



Soil covered with vosetation 

 (Broadhalk wildciiicss) 



Rich garden soil 



Arable soil Broadlmlk 

 (lunged plot 



Broadbalk unmanured 



.■{.52 



400 



468 



p Approximate \ Percentage com - 



' volume of position of gas 



Weight 



of soil oentagc 

 used, I of 



grms ! Moisture '» successive 

 - e.xtractions 



gas reniove<i i_ 



22 



20 



extracted later 



24 



407 



IG 



1st .30 0.0. 



2nd 30 



3rd 15 



1st 30 e.e. 



2nd 30 



:!rd l."") 



* 4th 30 



/ .">th 30 



1st .30c.c. 



2nd 30 



3rd l.-) 



1st 30c.c. 



2nd 2.5 



CO, 



1st .30 CO. ' 520 

 2nd 30 84-8 



3rd 22 !K)1 



0, 



19-3 5-5 

 570 2() 

 98-7 0-2 



N, 



0-7 47-3 

 0-2 150 

 0-2 0-7 



75-2 



40-4 



11 



10-3 

 0-7 

 06 

 31 

 70 



84-8 



40-3 



1-6 



78-6 

 501 



It will be observed that the composition varies with the pressure, 

 and that the first samples withdrawn contaii\ more oxygen than the 

 last: the final samples are almost pure carbon dioxide. 



The volume of gas obtainable depends on the amount of moisture 

 in the soil as it is brought in from the field, and decreased as the soil 

 becomes dryer ; from which we may infer that the gas is partly dissolved 

 in the soil moisture, though part may be dissolved in other soil con- 

 stituents. 



Thus it appears that there are two atmospheres in the soil : one 

 present as free gas filling the pores, and practically as rich in oxygen 

 as ordinary air, the other dissolved in the surface films of water and 

 other substances, almost devoid of oxygen and consisting mainly of 

 carbon dioxide with some nitrogen. 



