QUALITATIVE AND QUANTITATIVE ANALYSIS 



79 



CARBON DIOXIDE EVOLUTION 



Evolution of carbon dioxide from soil, to which no fresh 

 quantities of undecomposed organic matter are added, is best 

 determined using 1-kilogram quantities of soil. Fresh, sieved 

 soil is placed in small unglazed porcelain pots holding just about 

 1 kilogram of soil. The pots are placed upon wooden bases and 

 covered with bell jars, which are sealed down to the stand with 



r 



D£ 



Fig. 3.- 



-Apparatus for the study of the influence of plant growth upon the 

 evolution of CO 2 from soil. {Neller.) 



paraffin. Air, freed from carbon dioxide by passing through soda- 

 lime and through bottles containing 10 per cent sulphuric acid, is 

 drawn through the bell jars, by means of glass tubes passed 

 through the wooden stands. The air is then drawn through 

 absorption towers containing 50 cubic centimeters of barium 

 hydroxide solution. 



When the decomposition of fresh organic matter in soil is 

 studied, 100-gram quantities of soil may be used. Long-necked, 



