338 GASOMETRIC-VOLUMETRIC METHODS 



Acid Phosphate Buffer. Same as for nitrogen (page 336). Carbon 



dioxide has a low solubility in this soln. 

 10% Sodium Hydroxide. 

 Glycerol. , 



PROCEDURE 



1. Lubricate the rear part of the dry plunger with a few streaks 

 of glycerol and place it in the syringe barrel which is moist with 

 water, 



2. Fill the glass cup with distilled water, draw it one fourth down 

 the barrel, ind expel it through the cup. Leave the dead space in 

 the syringe full of the water without trapping any air bubbles. 



3. Pull out the plunger slightly so that the water meniscus at 

 the bottom of the cup is lowered 1-2 mm. down into the capillary. 



4. Hold the pipette against the opening of the capillary, trapping 

 a small air bubble, and draw the sample (13 [A.) down very slowly 

 into the capillary with the air separating it from the water. 



5a. With the meniscus of the sample at the 30 or 35 mark, detach 

 the pipette and suck out the sample from the cup. Slowly move the 

 upper meniscus of the sample to the zero mark, and read the amount 

 of sample b (page 340) in divisions. 



5b. As an alternative procedure, move the sample down to a 

 mark made at 33.3 divisions. Adjust the upper meniscus exactly to 

 the zero mark with a fine suction tip, keeping the lower meniscus 

 at the 33.3 mark. (In this way one third the normal pipette load is 

 used and the carbon dioxide vol. has only to be multiplied by 3 to 

 give the carbon dioxide content in volumes per cent after correc- 

 tions for temperature, etc.) 



6. Deposit a drop of caprylic alcohol on the bottom of the cup 

 and eject the bubble of air above the sample through the caprylic 

 alcohol with the aid of a piece of fine wire if necessary. 



7. Same as step 6 in the oxygen method (page 333) . 



8. Fill the glass cup to the mark with acid phosphate and draw 

 it down very slowly until the upper meniscus is 2 mm. below the 

 bottom of the cup. 



9. Moisten the rubber end of the wooden plug with phosphate 

 buffer and, with a few drops adhering to it, insert it in the bottom 

 of the cup, trapping a small air bubble. 



10. With the plug resting loosely against the bottom of the cup, 

 gently move the air bubble up until it touches the rubber tip. Then 



