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GENERAL MICROBIOLOGY 



fermentation tube each day if gas is being formed. (If 

 the level is higher than it was the previous day, the gas 

 (CO2) is being absorbed. Do not allow this absorption 

 to proceed further, but test the gas present for C02 

 and H 2 ). 



6. Measure and record the amount of gas by means of a 

 gasometer (see illustration). The total amount is not 



FIG. 36. Smith's Fermentation Tube Showing use of Frost's Gas- 

 ometer. 



exact quantitatively, as some gas is given off from the 

 open arm of the fermentation tube. 



7. When the maximum amount of gas is formed, test 

 the gas for C02 and other gases as follows: 



Fill the short arm of the fermentation tube with 10% 

 NaOH. Place the thumb over the mouth of the tube and 

 shake vigorously, so that the gas contained in the long 

 arm comes in contact with the NaOH. 



2NaOH+C0 2 = Na 2 CO 3 +H 2 O. 



