138 METHODS FOR THE ANALYSIS OF BLOOD 



MICRO-TITRATION l 



When it is desirable to employ only small amounts of plasma, 

 0.400 c.c. may be transferred to a test-tube of about 20 mm. 

 diameter, and 1 c.c. of 0.002 N HC1 added. The tube is laid in 

 a nearly horizontal position, so that the layer of liquid extends 

 for about 10 cm. along the lower side. The tube is then rotated 

 or rolled back and forth vigorously, but not so roughly as to cause 

 foaming, for not less than 1.5 minutes, in order to cause the car- 

 bon dioxide to escape. Three drops of indicator are then added, 

 and the solution is titrated in the test-tube with 0.004 N NaOH 

 to a pH of 7.4, using as a color standard a like volume of phosphate 

 solution in a similar tube. 



The 0.004 N NaOH is so rapidly altered by contact with either 

 glass or atmospheric carbon dioxide that it is advisable to make 

 it fresh for each series of analyses by diluting 10 c.c. of 0.1 N NaOH 

 to 250 c.c. with distilled water that has been freed of CO2 either 

 by boiling or by shaking in an evacuated flask. The control 

 titration of the 0.004 N NaOH against the 1 c.c. of 0.02 N HC1 

 should be performed immediately before the plasma titration. 



The calculation is the same as in the larger titration. The 

 number of c.c. of 0.004 N NaOH used is subtracted from the 

 number of c.c. (approximately 5) required to neutralize the HC1 

 in the control titration. The difference divided by 100 represents 

 the molecular concentration of bicarbonate in the plasma, while 

 the difference multiplied by 22.4 indicates the volume per cent 

 of bicarbonate CO2. 



With care in the calibration of pipettes, and especially in the 

 control of the 0.004 N NaOH, results nearly and perhaps quite as 

 accurate as in the larger titration appear attainable. 



ALKALI RESERVE 



Indirect Method. Alveolar Carbon Dioxide Tension 

 Marriott's Method"* 



While this method is open to criticism because of the liability 

 of error in the collection of the sample and, more fundamentally, 



1 Jour. Biol. Chem., 1919, 38, 177. 



2 Marriott: Jour. Am. Med. Assn., 1916, 66, 1594. 



