The Intake of Carbon 221 



collected is to be tested as to oxygen content by means of potas- 

 sium pyrogallate. 1 Unfortunately this solution would also absorb 

 another gas, carbon dioxid, so it is necessary to test first for carbon 

 dioxid. This is accomplished as follows : Clamp pinch-cock (G), 

 remove the series of tubes from the support, and pour out water be- 

 low ((?), invert and fill (E) with a weak solution of potassium hy- 

 drate (an absorbent of carbon dioxid) until the liquid rises in (Z>), 

 then clamp (H) securely, open ((?), and shake so that tLe CO 2 in 

 (F) will be absorbed. Fill (D) with water, close with a finger, and 

 again open the series under water to liberate any tension from 

 absorption of CO 2 . If there is any change in the volume of gas 

 in (F), note this, or indicate by a new label. Next, to absorb 

 the oxygen, proceed in the same manner as before, except that 

 fresh potassium pyrogallate is to be substituted for the potas- 

 sium hydrate solution ; also the shaking, in order to absorb all 

 the oxygen, should be continued for several minutes. When the 

 tension is again released by inversion over water, the difference 

 between the preceding and present displacement will show the 

 volume of O 2 caught during the experiment. Compare this with 

 the volume per cent of oxygen in the air. As a check on the 

 accuracy of manipulation, introduce ordinary air into the tube 

 series, and then determine the volume of oxygen. (If graduated 

 tube (F) is not available, accurate measurements may be made 

 after the experiment is complete by filling, from a graduated 

 pipette or burette, the tube to the points marked with labels 

 in order to determine the volumes indicated.) 



In case the experiment is stopped for any purpose, as on 



1 The potassium pyrogallate solution now strongly recommended by 

 Ganong consists of "1 part pyrogallic acid to 5 parts caustic potash to 

 30 parts of water." With this quantity of caustic potash 1 gram of the 

 pyrogallate may absorb $ gram of oxygen; but for uncontrolled experi- 

 ments it is well to figure at the rate of not less than 1 gram of pyrogallic 

 acid to ^ gram of oxygen. The solution deteriorates rapidly, even in 

 diffuse light, and should be made up immediately preceding its use. 

 It is preferably made by using equal parts of two solutions, each con' 

 tainiug one of the constituents in double strength. 



