RESPIRATION AND ACIDOSIS 319 



with those obtained by the CO 2 method. The standard 0.02 N NaOH must be 

 protected from atmospheric CO 2 and kept in paraffined bottles to prevent solution 

 of alkali from the glass. The burette should be filled with fresh solution each 

 day. The carbonate-free solution is made by dissolving the NaOH in an equal 

 volume of H 2 O. On standing the Na 2 CO? settles to the bottom. 5.5 c.c. of the 

 clear supernatant solution is diluted to 5 L. and standardized by titration with 

 neutral red against 0.02 N HC1. It is preferable to run the acid into the alkali as 

 the color change occurs without the time lag observed when alkali is added to acid. 



A micro-titration method is also described in which the determination can be 

 made with 0.4 c.c. of plasma. If special care is taken in the calibration of pipettes 

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

 accurate as in the larger titration appear attainable. 1 



Interpretation. The results agree closely with those of the CO 2 capacity method 

 over the range of bicarbonate concentrations (0.03 to o.oi M) ordinarily encoun- 

 tered in man, even in severe acidosis. Below this range the titration continues to 

 give accurate results, while the CO 2 capacity method gives somewhat higher 

 values. For clinical and most experimental purposes, however, it appears that the 

 two methods give so nearly identical results that they may be used interchangeably. 



2. Alkali Reserve. Indirect Method. Alveolar Carbon Dioxide 

 Tension. Fridericia's Method. 2 



Principle. The method of determination is based upon the absorp- 

 tion, by means of potassium hydroxide, of the carbon dioxide from a 

 known amount of alveolar air. The apparatus is so graduated that 

 the decrease in volume may be read in per cent. 



Procedure. The subject must sit quietly in a chair and breathe naturally, 3 

 holding the apparatus (shown in Fig. 103) in front of him with the cock a 

 open and b in a position connecting x with y. After taking a normal inspi- 

 ration he places the mouthpiece m into his mouth and blows as hard and as 

 quickly as possible through the apparatus thus washing it out and leaving it 

 filled with alveolar air. The cock a is at once closed and the whole apparatus 

 is immersed in water for 5 minutes. By this means the alveolar air in x and y 

 is cooled to a temperature which remains constant throughout the experiment, 



1 Testing Standard 0.02 N NaOH for Carbonate. The solutions should be made up 

 using only boiled water, be kept in paraffine-lined bottles, and be protected from atmos- 

 pheric CO 2 by soda-lime tubes. They should be tested for carbonate as follows: 



To 5 c.c. of 0.02 N HC1 in a 200 c.c. round flask, add from a freshly filled burette about 

 4.8 c.c. of the 0.02 N NaOH to be tested, 0.3 c.c. of neutral red solution. The mixture 

 should be strongly acid to the indicator. The solution is rotated for one minute in the 

 flask to permit the escape of CO 2 , and is then transferred to a 50 c.c. Erlenmeyer flask 

 and titrated as in plasma analyses, the total amount of 0.02 N NaOH required to give the 

 end point being noted. 



A duplicate titration is performed in the same way except that there is no agitation 

 to remove carbon dioxide, the 0.02 N HC1 plus 20 c.c. of water being placed directly in the 

 50 c.c. Erlenmeyer flask, and the 0.02 N NaOH being added with a minimum of stirring. 



If there is no carbonate in the standard NaOH solution the two titrations give identical 

 results. The difference should preferably not exceed o.i c.c., and if it exceeds 0.2 c.c. the 

 alkali should not be used. 



2 Fridericia: Hospitalstidende, Copenhagen, 57, 585, 1914; Poulton: Brit. Med. 'Jour., 

 2, 392, 1915. 



3 It is especially important to caution the subject against the very natural inclination 

 to take an abnormally deep inspiration just before blowing through the apparatus, and 

 also to see that, in seeking to avoid this fault, the breath is not held just before the sample 

 is taken. 



