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LABORATORY MANUAL OF MICROBIOLOGY 



Silica gel containing macerated cellulose on surface may also 

 be used for the isolation of cellulose-decomposing bacteria. 



Exercise 58 



The Evolution of Carbon Dioxide from Soil 



Weigh out 100 grams of well mixed soil into 500-cubic centi- 

 meter Erlenmeyer flasks or other suitable vessels. Arrange as 

 follows : 



1. Control, soil alone. No treatment. 



2. Soil plus 1 per cent of glucose, starch, cellulose, alfalfa meal, 

 blood meal or similar substances in the powdered form. 



Bring the moisture content of the soil to two-thirds saturation. 



Fig. 19. — Apparatus for measuring carbon dioxide evolution from soil. 



After the test substance is well mixed with the soil set up the 

 apparatus in such a way that the CO2 evolved will be absorbed 

 in 25 cubic centimeters of 0.2 N Ba(0H)2 solution in a large test 

 tube. The large tower A of Fig. 19 is filled with soda-lime and 

 connected to B with a glass tube. The end of this tube carries a 

 gas washing tube. B is filled about two-thirds full of water and 

 connected to C. In this way moist CO2 free air is carried to C, 

 In flask C is the soil sample. £' is a test tube containing the 

 Ba(0H)2 solution. The gas is dispersed into fine bubbles by 

 means of a Rose end tube. D is a trap to catch the alkali solu- 

 tion in E if there is any back pressure, and the alkali in E sucks 

 back. As soon as possible, after the soil is mixed with the 

 various substances, begin a slow aeration at the rate of one 



