CARBON DIOXIDE 



339 



press the plug against the bottom of the cup, leaving the bubble in 

 contact with the rubber {A, Fig. 108) . Keep the capillary closed in 

 this way with the left hand throughout steps 11-17. 



11. Place fresh glycerol in the plunger bearing. 



12. Place one end of the metal spacer around the plunger under 

 the plunger head, and hold it there with the other end sticking out 

 at an angle. Keep the cup end of the syringe pointing upwards at a 

 slant through the steps 13-16. 



(s> 



i 



Fig. 108. A, Rubberized wooden plug for 

 vacuum-sealing the glass cup. B, spacer for keep- 

 ing the plunger extended in a fixed position dur- 

 ing the vacuum extraction. From Scholander and 

 Roughtnn (1943b) 



13. Slowly move the plunger out so that the fluid meniscus 

 under the stopper moves down the capillary very slowly. When the 

 capillary and its opening into the barrel are drained of fluid, slowly 

 draw the plunger out and move the free end of the spacer in until it 

 fits against the syringe barrel {B, Fig. 108) . 



14. Add glycerol to the plunger bearing. 



15. Shake the syringe for 2 min. with the cup end up to prevent 

 fluid from blocking the opening to the capillary. Should the capillary 

 become occluded, clear it by warming the capillary with the hand. 

 Should foaming occur, release the plunger and draw it out again. 



16a. With the capillary free from fluid, pull out the plunger to 

 allow the spacer to fall out. Allow the plunger to rise rather rapidly 

 until the lower meniscus is inside the capillary and the gas pressure 

 is atmospheric. 



16b. Should fluid bridge the opening to the capillary while the 

 plunger is let in, adjust the speed of the plunger so that the bridge 

 moves slowly up the capillary to enable proper drainage to occur. 



17. Remove the plug and move the upper meniscus slowly and 

 evenly to the zero mark when the gas bubble is at atmospheric 

 pressure. 



