554 Adeney — Dissolved Gases and Fermentative Changes. 



When the necessary adjustments have been made, the height of the mercury 

 in the pressure tube, which, I should Iiere note, is kept moist, is read off, the line 

 of measurement on the burette and the temperature of the water in the jacket, are 

 also noted. The next step is to absorb the carbon dioxide ; the small quantity of 

 solution of potassium hydrate required for this purpose is introduced into the 

 laboratory vessel thus : — the stopcock of the burette is closed, the reservoir of the 

 laboratory vessel is fixed well above the level of the reagent tube, and a pi^oette 

 containing the solution of potassium hydrate is connected to the free end of the 

 rubber tube attached to the reagent tube, and then left supported, as indicated in 

 the drawing. 



As the reservoir is now above the level of the reagent tube, on unscrewing the 

 clamp the mercury will flow into the pipette, and expel any small bubble of air 

 that may have been left in the open end of the rubber tube after attaching the 

 pipette to it. The air having been completely expelled, the clamp is screwed 

 up again, and the reservoir dropped to a level a little below that of the reagent 

 tube. 



On carefully opening the clamp the mercury in the pipette will slowly flow 

 back into tlie laboratory vessel, and after it the required amount of potash solution, 

 care being used so as not to empty the pipette entirely. As soon as this is 

 accomplished, the clamp is closed, and the reservoir raised to about its former 

 level. The surplus quantity of solution remaining in the reagent tube may now be 

 driven back into the pipette, and after it a little mercury, by carefully opening 

 the clamp, which is closed again immediately this has been done. To effect the 

 absorption of the carbon dioxide by the potash, the gas is passed into the 

 laboratory vessel, and then backwards and forwards into the burette three or four 

 times, care being taken not to allow any of the potash into the burette. In about 

 five minutes the carbon dioxide will be completely absorbed, and the remaining 

 gas again measured just as before, and the height of the mercury in the pressure 

 tube noted, the difference of reading before and after absorption giving the 

 pressure exerted by the carbon dioxide at the volume at which the gases have 

 been measured. 



If the volume of this gas has been large, it will reduce the errors of reading in 

 the further process of analysis, if the remaining measurements be made at a 

 volume less than that which was necessary before absorbing the carbon dioxide. 

 The operation of absorbing the oxygen by means of pyrogallic acid is carried on 

 similarly to that for absorbing the carbon dioxide. The remaining gas will 

 consist, at least in moat cases, of pure nitrogen. Its pressure at the volume at 

 which the measurements for the determination of the oxygen were made, is easily 

 determined by deducting from the last noted pressure the height of mercury in 

 the presure tube corresponding to the height of mercury in the burette at the line 



