418 



ILLUSTRATIVE EXPERIMENTS 



cent, (alcoholic) neutral red. The optical effect of the turbidity of the 

 plasma may be counteracted by placing a sheet of white tissue paper behind 

 the tubes. The plasma mixture is titrated with N/50HC1 (2 c.c. burette 

 with fine nose) till its colour matches the standards. This is done by run- 

 ning the plasma into the flask, adding a few drops of acid and rotating 

 gently but steadily for 1 minute, the flask meanwhile being in communica- 

 tion with the air. This readily allows the thin film of plasma to give up 

 the liberated C0 2 . The fluid is run back into the tube and compared with 

 the standards. The process is repeated as often as necessary. Rotation 

 for at least 1 minute is necessary after each addition of acid. 



Titration value for 0-5 c.c. plasma =0-77 c.c. N/50HC1, 

 i.e. Alkali reserve of = 0-77 c.c. N/50NaHC0 3 

 ,, 100 c.c. ,, =154 c.c. ,, 



= 3-08N 



= 3-08x22-4 c.c. C0 2 , 



i.e. 68-99 volumes per cent, of C0 2 are bound as bicarbonate in the plasma. 



A sharper end-point is obtained by the 

 use of phenol sulphonephthalein as in- 

 dicator. In this case the standard 

 phosphate solutions are made of pH 7-2 

 to correct the protein error. 



43. Alkali Reserve by Van Slyke's 

 Method. The Van Slyke apparatus is 

 illustrated in Fig. 79. It consists essen- 

 tially of a 50 c.c. pipette with three-way 

 stopcocks (e and /) at top and bottom, 

 and a 1 c.c. scale on the upper stem, 

 divided into 0-02 c.c. divisions. The 

 body of the apparatus is connected 

 through heavy walled rubber tubing 

 with a levelling bulb filled with mercury. 

 The whole apparatus is supported on a 

 stand so that, without unclamping, the 

 pipette may be rotated round a central 

 axis. The stopcocks are lubricated with 

 a rubber-vaseline mixture and may be 

 held in place by strong rubber bands. 



Preliminary preparation. Open taps e 

 and / and fill the entire apparatus with 

 mercury by raising the levelling bulb, 

 allowing some mercury to run into a and 

 into b. Shut e, and lower the levelling 

 bulb till the mercury falls half-way down 

 c and d. The bulb is then slowly raised. 

 If the apparatus is gas-free, a sharp click 

 will be heard when the mercury strikes 

 the upper stopcock. If a gas cushion is 



FIG. 79. Apparatus for Estimation of present, open e, and force the gas out, 



and repeat the evacuation process, 

 opening / alternately to c and d. 



Determination. (1) Solutions required. It is convenient to have four 



