OXYGEN 333 



4. Draw the sample from the pipette, which has been filled to 

 the mark (about 40 fA.) into the capillary as shown in Fig. 106. 

 Pull out the plunger gradually so that the sample is slowly and 

 evenly drawn in followed by an air bubble of about 1 mm. length 

 (A and B, Fig. 107) . The air bubble prevents the blood from getting 

 back up into the pipette. If the pipette tip is properly ground and 

 the correct pressure applied during the transfer, no appreciable 

 quantity of caprylic alcohol will be drawn into the capillary. 



5. Remove the pipette quickly, and expel the air bubble {C, Fig. 

 107) through the caprylic alcohol, using a fine wire if necessary or 

 tapping the capillary. 



6. Draw in a column of the caprylic alcohol two divisions in 

 length onto the top of the blood and suck out the rest of the 

 caprylic alcohol from the cup. 



7. Fill the cup to the mark with acetate buffer and draw it down 

 to the bottom of the cup. 



8. Immediately fill the cup to the top with 45% urea and close 

 firmly with the finger. 



9. Shake the closed apparatus vigorously for 2 min. in a hori- 

 zontal position, gradually pulling out the plunger as the gases are 

 evolved to keep the gas pressure in the syringe about 1 atmosphere. 

 About 0.75 ml. is usually evolved (Fig. 104) . The amount of carbon 

 dioxide evolved may be varied by changing the strength of the 

 bicarbonate in the ferricyanide soln. 



10. Carefully release the finger while adjusting the plunger to 

 keep the gas meniscus in the capillary. Let a little urea soln. run 

 down into the capillary, and allow it to remain there until the walls 

 are perfectly clean. 



11. Remove three fourths of the urea soln. from the cup. Fit the 

 rubber cap over the glass cup, and fill it with 10% sodium hydroxide 

 without trapping air bubbles {A, Fig. 105). 



12. Draw a little of the alkali into the syringe. As the carbon 

 dioxide is absorbed more alkali will be sucked in until only a small 

 bubble of the other gases will remain {B, Fig. 105). The absorption 

 requires a few sec, and, before it is complete, carefully move the 

 residual bubble into the capillary to prevent reabsorption of oxygen. 



13. Remove the rubber cup. Empty the glass cup, and set the 

 capillary in a beaker of water at room temperature for 30 sec. (C, 

 Fig. 105). 



