336 GASOMETRIC-VOLUMETRIC METHODS 



Edwards. Scholander, and Roughton Method for Nitrogen 



SPECIAL REAGENTS 



Bicarbonate Solution. Dissolve 11 g. potassium bicarbonate in 100 

 g. water. 



Acid Phosphate Biiffer (about 5 M). Dissolve 95 g. sodium dihy- 

 drogen phosphate (NaH2P04.H20) in 100 g. warm water. 



Hydrosulfite Solution. To 50 ml. of 20% potassium hydroxide add 

 15 g. of a mixture of 10 parts sodium hydrosulfite and 1 part 

 sodium anthraquinone-^-sulfonate. Store well stoppered in con- 

 tact with as little air as possible. 



45% Urea. 



Caprylic Alcohol. 



Aerated Distilled Water. 



PROCEDURE 



1. Same as for oxygen (page 332) substituting the bicarbonate 

 soln. for the ferricyanide. 



2. Dry the glass cups with cotton or filter paper and place a drop 

 of caprylic alcohol in the bottom of the cup without trapping air 

 bubbles. 



3-5. Same as steps 4-6 in oxygen method (page 333). Take care 

 to prevent caprylic alcohol from being drawn down into the capil- 

 lary with the sample. A 120 ;ul. sample is used. 



6-9. Same as steps 7-10 in oxygen method (see page 333) 

 substituting the acid phosphate bufi'er for the acetate. Draw the 

 urea soln. down to the bottom of the capillary but do not let it enter 

 the syringe barrel. 



10. Holding the syringe vertically, attach the rubber cap, and 

 add about 1 ml. hydrosulfite soln. without trapping air bubbles in 

 the glass cup. 



11. Draw a little hydrosulfite into the syringe; the vacvmra 

 created by the gas absorption will draw in the rest of the soln. 

 required for the complete absorption of the carbon dioxide and 

 oxygen. 



12. Push the bubble up into the lower part of the capillary; 

 suck out the hydrosulfite ,from the rubber cap and detach the latter. 

 Fill the glass cup with water, and draw three fourths of it down over 

 the bubble. 



