OXYGEN RESPIRATION 37 



opened, and in this way a suitable quantity of potash is sucked 

 into the pipette, after which the end of the pipette is let into 

 the mercury by raising the analysis tube, and mercury is drawn 

 into the pipette for a time in order to remove the lye that 

 adheres to the walls of the capillary tube. After filling the 

 pipette, the potash solution contained within the bulb is thus 

 sealed by the mercury in the capillary tube above it. 



The determination of oxygen in the apparatus of Polowzow- 

 Richter is done by combustion with hydrogen. Hence, hydro- 

 gen and oxy-hydrogen gas are required for the analysis. These 

 gases are prepared by electrolysis according to the detailed 

 directions of Bunsen^ and stored in thick-walled test tubes 

 which are sealed with mercury. 



The apparatus must be carefully calibrated before use. The 

 accuracy of the analysis depends above all on the accuracy of 

 the calibration. The absolute volume of the bore of the 

 measuring tube is unknown and for measuring the percentage 

 composition of the gases to be analysed is unimportant. But 

 it is very important to rectify by suitable corrections the 

 inequality of the volumes contained between millimeter mark- 

 ings, due to the inaccurately cylindrical form of the measuring 

 tube. This is done as follows. One incloses with mercury in 

 an analysis tube a couple of cubic centimeters of air, transfers the 

 analysis tube to the bath C, places it under mercury on the end 

 of the measuring tube, lowers the pear-shaped bulb H and sucks 

 into the measuring tube, by opening the stopcock a, first some 

 air, then a small quantity of mercury, and finally some more air. 

 This procedure is analogous to filling the absorption pipette with 

 potash solution as described above. The volume of the 

 mercury introduced must be scarcely larger than or at best exactly 

 as large as the space between O and o. If too much mercury 

 has been drawn in the surplus is removed with the aid of the 

 screw e. The introduced mercury column is so suspended that 

 the top of the meniscus in the right side coincides with the line 

 O, and by the use of the reading microscope the position of the 

 highest point of the other meniscus in the left-hand, wide side 

 of the tube is then noted. The column of mercury is next 



I Bunsen, R. Gasomethrischen Methoden. 2nd. ed. Pp. 76 and 80. 1877. 



