THE EXAMINATION OF CULTURES 51 



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 CO 2 which has been absorbed by 

 the caustic soda. Measure the portion of the tube first occu- 

 pied with gas and now filled with the liquid. This will indi- 

 cate the quantity of CO 2 . The remainder of the gas is H. 

 (There are also traces of other gases.) Its explosive property 

 can be tested by filling the open bulb with water, covering it 

 with the thumb and again bringing the gas to the open bulb, 

 holding it close to a flame, and removing the thumb. A dis- 

 tinct explosion will be heard. 



The ratio, of CO 2 to H can be determined from the meas- 

 urements. Thus the total amount of gas in the closed branch 

 = 5 cm. The amount absorbed (CO 2 ) = 2 cm. The remain- 

 ing gas, or 3 cm., = H. The ratio of CO 2 to H is, therefore, 

 as 2 : 3, or CO 2 : H : : 2 : 3. 



