66 PLANT RESPIRATION 



anaerobic respiration, the value of the respiratory quotient in 

 the normal respiration must also be obtained. 



There remains to be described here first, the methods of 

 removal of oxygen and secondly, the methods of determination 

 of alcohol. In general, if no quantitative determinations are 

 to be carried out it suffices to confine the plants in a suitable 

 container and then to absorb the oxygen with alkaline pyro- 

 gallol solution. Ordinary exsiccators are very well suited to 

 this purpose. A concentrated solution of caustic potash is 

 poured into the lower part of the exsiccator and an easily 

 overturned dish of concentrated pyrogallol solution is placed 

 in the lye. The plant material is then placed in position, the 

 exsiccator well sealed, and the Kttle dish of pyrogallol solution 

 is upset. The oxygen is absorbed and the plants are left under 

 anaerobic conditions. Assertions are found in the literature to 

 the effect that some carbon monoxide is formed at times when 

 oxygen is absorbed by alkaline solutions of pyrogallol. This 

 situation can be disregarded since carbon monoxide represents 

 an inert gas for plants.'' 



The atmospheric air must be replaced by an inert gas for 

 quantitative determinations of the products of anaerobic respi- 

 ration. If the work is done in a current of gas it is usually 

 preferable to use hydrogen, because this gas is easy to admit in 

 large quantities and sufficiently pure. The apparatus of Barde- 

 leben (Fig. ii) is more commendable than the ordinary Kipp 

 generator for the continual passage of hydrogen, since the 

 latter cannot be filled with fresh acid without interrupting the 

 gas current and requires a larger amount of acid for the produc- 

 tion of the same quantity of gas than does the Bardeleben 

 apparatus. The latter consists of a large glass cyUnder which 

 is filled with the purest dilute sulphuric acid. Concentrated 

 sulphuric acid is diluted with three times its volume of water 

 and enough copper sulphate is added to color the .solution 

 bright blue. In the acid is set a glass bell jar which is closed 

 above with a one-hole rubber stopper. In the hole of the stop- 

 per is inserted an exit tube with a glass stopcock. Under the 



•^ The concentration of carbon monoxide produced l)y this action must be very 

 low and hence is cjuite negligible.^/i</. 



