ALKALI RESERVE 



141 



great enough to affect the value as much as 1 mm. and therefore 

 may be neglected.) 



Calculation. The standard tubes are marked to indicate the 

 carbon dioxide tension in millimeters of mercury, and the readings 

 can be estimated to about 2 mm. 



ALKALI RESERVE 



Indirect Method. Alveolar Carbon Dioxide Tension 

 Fridericia's Method 1 



Principle. The method of determination is based upon the 

 absorption, by means of potassium hydroxide, of the carbon 

 dioxide from a known amount of alveolar 

 air. The apparatuses so graduated that 

 the decrease is volume may be read in per 

 cent. 



Procedure. The subject must sit quiet- 

 ly in a chair and breathe naturally, holding 

 the apparatus (shown in Fig. 12) in front 

 of him with the cock a open and 6 in a 

 position connecting x with y. (It is es- 

 pecially 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.) After taking a 

 normal inspiration he places the mouth- 

 piece ra into his mouth and blows as hard 

 and as quickly as possible through the ap- FIG. 12. Fridericia Appa- 

 paratus, thus washing it out and leaving ratus. (Hawk.) 

 it rilled with alveolar air. The cock a is at 



once closed and the whole apparatus is immersed in water for 

 five minutes. By this means the alveolar air in x and y is cooled to 

 a temperature which remains constant throughout the experi- 

 ment, and the contraction in volume causes the alveolar air in 



Fridericia: Hospitalstidende, Copenhagen, 1914, 57, 585. Poulton: 

 Brit. Med. Jour., 1915, 2, 392. 



