OXYGEN RESPIRATION 45 



dilute nitric acid and then three times with distilled water. If 

 a still smaller degree of accuracy is needed for the purpose of the 

 study, one may desist from the use of the various apparatus for 

 gas analysis and make use of simpler devices. There is, for 

 example, the respiratory apparatus of Godlewski^ which is 

 constructed as follows: a thick- walled, calibrated flask provided 

 with a manometer tube serves as a container. A small vessel 

 containing a measured amount of concentrated caustic potash 

 is suspended within the flask, which is tightly sealed. As soon 

 as the plants begin to take up oxygen and to give ofif CO2, the 

 latter is absorbed by the potash. Consequently the air pres- 

 sure in the apparatus is diminished and the mercury begins to 

 rise in the manometer tube. The lowering of the pressure at 

 the same time yields, by simple calculation, the volume of 

 oxygen absorbed. The carbon dioxide which is given ofif is 

 determined at the close of the experiment. The solution of 

 potash is diluted with a large volume of water and the CO2 

 determined in the form of BaCOs. For the various corrections 

 which are essential with this method the original communication 

 of Godlewski must be consulted. 



In the simultaneous determination of the absorbed oxygen 

 and the carbon dioxide given off, of course there must be used 

 containers into which plants can be sealed air-tight and which 

 provide for the removal of test portions for analysis. Kosty- 

 chev used to advantage conical flasks which are also useful 

 for cultures of lower organisms on liquid or solid media (Fig. 8). 

 The capacity of each flask is 200-500 cc. and each is closed by a 

 two-hole rubber stopper fitted with an entrance and an exit 

 tube.- The distension C in the neck of the flask above the 

 stopper is filled with mercury and a completely air-tight seal is 

 thereby obtained. The outer, vertical side of the exit tube h is 

 calibrated and serves as a manometer. The flask containing 

 the plant material is closed as above, the manometer tube 

 inserted in mercury and the entrance tube a connected by means 

 of a thick-walled rubber tube with the gas pipette (see below) 



1 Godlewski, E. Jarhb. f. wiss. Bot. 13 : 49i- 1882. 



2 For cultures of lower organisms it is practical to place close to the bottom of the flask a 

 side tube closed by rubber tubing and a pinchcock. A change of nutrient solution can 

 easily be effected through it, as is often necessary. 



