150 



SOIL BACTERIOLOGY 



by inclining the end of the pipet into the flask and pouring 

 the wash-water on to the beads. Washing should be re- 

 peated until all traces of alkaU have disappeared. Place 

 a few drops on a watch-glass containing phenolphthalein. 

 If there is no change in color, the washing is complete. 



V 



Fig. 10. — Apparatus for determining carbon dioxid. 



Avoid using too large a quantity of water for each washing, 

 otherwise the volume of liquid to titrate will be very large. 



iVo/e.— Carbon-dioxid-free water may be prepared by drawing a current 

 of carbon-dioxid-free air through distilled water for twenty-four hours or 

 longer. 



