54 



Examine the fermentation tubes and indicate the quantity 

 of gas, and the ratio of gas to liquid in the closed branch. 



Determine the ratio of COj to H in the gas. 



In studying these cultures they should be examined each 

 day and the quantity of gas indicated. Note the bubbles of 

 gas rising through the liquid to the top. When the gas pro- 

 duction has ceased the liquid begins to clear near the surface 

 in the closed branch. The final record should not be made 

 until this occurs. The reaction of the culture should be de- 

 termined and noted. 



Inoculate a tube of bouillon and make a series of three 

 agar plates for Kxercise XXIII from a mixed or impure 

 culture, which will be furnished. 



§ 84. Determine the quantity of gas. It is desirable 

 to determine the quantity of gas collected in the closed branch 

 in terms of the capacity of the tube. To do this measure the 

 length of the closed branch and the length of that portion of 

 the tube filled with gas. Thus if the length of the tube is 

 10 cm. and the length of the portion filled with gas is 3 cm. 

 the gas fills y\ of the branch. This can not be determined 

 until the gas formation has ceased which sometimes requires 

 several (4 to 6) days. 



§ 85. Determine the ratio of the CO^ to H in the gas 

 produced. This can be approximately determined by the 

 use of caustic soda. Remove the plug from the fermenta- 

 tion tube and fill the open bulb with a 2 % solution of caustic 

 soda. Place the thumb tightly over the open end of the 

 tube and tip it up so that the gas will pass through the 

 liquid and come into the open bulb. It is then returned. 

 This should be repeated several times. Remove the thumb 

 , when the open bulb is full and the liquid will rush up into 

 the closed branch to fill the space occupied by the COj which 

 has been absorbed by the caustic soda. Measure the portion 

 of the tube first occupied with gas and now filled with the 

 liquid. This will indicate the quantity of CO,. The bal- 



