NITROGEN AND CARBON DIOXIDE 337 



13. Push the bubble up into the clean capillary very gently. 

 Equilibrate the temperature and read the volume (Fi) in divisions 

 (steps 13, 14, pages 333 and 334). 



14. Run a blank on the reagents by substituting aerated distilled 

 water for the blood; however, use one third the vol. of water, i.e., 

 to the first mark on the pipette (about 40 i-d.) . The blank then 

 equals V — (a//) where V is the uncorrected nitrogen reading, a is 

 the solubility of atmospheric nitrogen in water at room temperature 

 in volume per cent (at 22°, a = 1.2), and / is the correction factor 

 (page 334). The authors of the method found the blai\k to be con- 

 stant and of the order of 1.3 to 1.5 units on the capillary, depending 

 on the instrument used. 



15. Calculate the nitrogen content of the blood from the formula: 



Nitrogen = (T\ - C) (//3) 

 where C is the blank correction for the nitrogen in the reagents. 



CARBON DIOXIDE* 



Certain changes in the syringe analyzer technique were intro- 

 duced by Scholander and Roughton (1943b) to enable the estimation 

 of carbon dioxide. The gases are vacuum extracted from the sample 

 mixed with acid buffer, and the gas volume is measured before and 

 after absorption with alkali. 



This determination requires a rubber-tipped wooden plug, made 

 by dipping the end of a round toothpick in rubber latex, leaving 

 a drop on the tip, and drying it, tip downward, at a moderate 

 temperature in an oven (A, Fig. 108). A spacer for holding out the 

 syringe plunger in a fixed position (B, Fig. 108) is also required. It 

 consists of a piece of light sheet metal, about 1.5 cm. wide and 5.5 

 cm. long, folded into a V-shaped channel. The length of the spacer 

 allows a gas space of about 0.75 ml. in the syringe. 



Srholander and Roughton Method for Carhon Dioxide 



SPECIAL REAGENTS 



Carbon Dio.ride-Free Distiller] Water. Boil the water after adding 



a drop of sulfuric acid. 

 Caprylic Alcohol. 



* See Bibliography Appendix, Ref . 52. 



