ALKALI RESERVE 131 



by fusing a capillary stop cock to a pipette graduated into 0.01 

 c.c. divisions.) 



It is not necessary that exactly 1 c.c. of wash water 

 and 0.5 c.c. of acid shall be taken, but the total volume 

 of the water solution introduced must extend exactly to the 

 2.5 c.c. mark on the apparatus, if the table on page 133 is to 

 be used. 



If the amount of plasma available is small a little more than 

 0.5 c.c. are saturated in a 50 c.c. funnel, and exactly 0.5 c.c. used 

 for the estimation of carbon dioxide. In this case the volume of 

 distilled water and acid used to wash the plasma into the apparatus 

 is halved, so that the total volume of water solution introduced 

 is only 1.25 c.c. and in the calculation the observed volume of gas 

 is multiplied by 2. 



After the acid has been added a drop of mercury is placed in 

 6 and allowed to run down the capillary as far as the cock in order 

 to seal the latter. Whatever excess of sulphuric acid remains in 

 the cup is washed out with a little water. 



The mercury bulb is now lowered and hung at position 3 and 

 the mercury in the pipette is allowed to run down to the 50 c.c. 

 mark, producing a Torricellian vacuum in the apparatus. When 

 the mercury (not the water) meniscus has fallen to the 50 c.c. 

 mark the lower cock is closed and the pipette is removed from the 

 clamp. Equilibrium of the carbon dioxide between the 2.5 c.c. 

 of water solution and the 47.5 c.c. of free space in the apparatus 

 is obtained by turning the pipette upside down fifteen or more 

 tunes, thus thoroughly agitating the contents. The pipette is 

 then replaced in the clamp. 



By turning the cock / the water solution is now allowed to 

 flow from the pipette completely into d without, however, allow- 

 ing any of the gas to follow it. The leveling bulb is then raised in 

 the left hand while with the right the cock is turned so as to con- 

 nect the pipette with c. The mercury flowing in from c fills the 

 body of the pipette, and as much of the calibrated stem at the top 

 as is not occupied by the gas extracted from the solution. A few 

 hundredths of a cubic centimeter of water which could not be 

 completely drained into d float on top of the mercury in the pipette, 

 but the error caused by reabsorption of carbon dioxide into this 

 small volume of water is negligible if the reading is made at once. 

 The mercury bulb is placed at such a level that the gas in the 



