SECTION IV 



RELATION OF MICROORGANISMS TO THE SULPHUR 

 CYCLE 



Exercise i 



Reduction of Sulphates with the Formation of Hydrogen 



Sulphid 



1. PREPARE three small bottles of sulphate solution 



(m. 55)- 



2. Inoculate as follows: 



(a) Uninoculated. 



(&) i gram of rich soil. 



(c) i c.c. of sewage slime. 



3. Stopper tightly with paraffined corks. 



4. Incubate at 28 C. for two or four weeks. 



5. At the end of this time remove bottles from incubator; 

 note the change in color and odor. 



6. Hold over the open mouth of the bottle a small piece 

 of filter-paper saturated with a solution of lead acetate. 

 A blackening of the paper shows the presence of hydrogen 

 sulphid. 



7. Remove a few cubic centimeters with a pipet to a 

 test-tube or small Erlenmeyer flask. 



8. Add a few drops of BaCl 2 solution. 



9. Compare the amount of white precipitate in the 

 inoculated cultures with that in the uninoculated control. 



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