THE STUDY OF MICROORGANISMS IN THE SOIL 137 



bubble per second. Every 24 hours, titrate the Ba(0H)2 solu- 

 tion to the phenolphthalein end-point with 0.1 iV oxalic acid 

 (6.3 grams per liter). Continue the absorption from day to 

 day until the CO 2 evolution declines to nearly a constant amount. 

 Barium hydroxide reacts with CO2 according to the following 

 equation : 



Ba(0H)2 + CO2 = BaCOs + H2O. O.IA^ Ba(0H)2 = O.IN 

 CO2 = 2.2 milligrams. 



The excess Ba(0H)2 is titrated with oxalic acid. The acid 

 neutralizes only the Ba(0H)2. Ba(0H)2 + (C00H)2 = Ba- 

 (C00)2 + 2H2O. 



The BaCO.s remains unchanged. The difference between the 

 excess of Ba(0H)2, as determined by oxalic acid titration, and 

 the Ba(0H)2 taken at the beginning, will give the amount of 

 Ba(0H)2 acted upon by the CO2. 



An example of the calculation follows : 



Ba(0H)2, O.IA^, factor 1.06 50 cubic centimeters 



Oxalic acid, O.IA^ 12.6 cubic centimeters 



50 X 1.06 53.0 cubic centimeters O.liV 



Back titration (oxalic) 12.6 



CO2 evolved 40.4 cubic centimeters O.liV 



Since 1 cubic centimeter O.IA^ 



Ba(0H)2 takes up 0.0022 gram CO2 



40.4 X .0022 0.0889 gram CO2 per 100 



grams of soil. 



When the CO2 evolution has declined to nearly a constant 

 amount, plot a curve showing the rate of evolution of the gas. 

 Plot milligrams of CO2 as ordinates, and days as abscissae. 



LITERATURE 



The following list includes some of tEe more important books that treat of 

 bacteriology : 

 A. General Bacteriology: 



Benecke, W. : " Bau und Leben der Bakterien," 2d Ed., Leipzig, 1924. 

 Buchanan, E. D. and R. E. Buchanan: "Bacteriology for Students in 

 General and Household Science," rev. Ed. 560 pp., 360 figs., New York, 

 1926. 

 Buchanan, R. E., and Fulmer, E. I.: " Physiology and Biochemistry of 

 Bacteria," 516 pp., Baltimore, 1928. 



