410 



= 1. In tlie manometer ?«, tlie liquid is equally high in iioth limbs, 

 whereas m, indicates a greater negative pressure than before. The 

 broken equilibrium, generated by tlie action of the sucking-and 

 forcing pump in the closed system is apparently shifted by the 

 opening and closing of /f5 in such a way, that in the res|)iratoi'y- 

 vessel (accordingly on the plants) no effective pressure can arise. 

 As soon as there disappears 0, from the closed system through 

 respiration, ?/i, will indicate it at once. When however an equal 

 quantity of 0, is added at the same time, ?h, will remain at zero 

 and the atmospheric pressure is preserved in the vessel. At the 

 oxygen, electrolytically produced in Z, enters the vessel. With the 

 aid of the resistance in the O^-development can be increased from 

 a minimum to a definite maximum. The intensity of the electrolytic 

 process may be thus regulated, that the Ü, -production keeps pace 

 with the O, -consumption. 



By increasing or reducing the resistance this equilibrium is soon 

 found and the manometer //;, indicates whether this condiiion is 

 preserved. It may happen (for instance by rise or fall of the respi- 

 ration-intensity), that for a moment there is a souiewhal greater or 

 smaller su[)ply of 0, to the apparatus. In this (^ase the height of 

 the manometer ?;/,, indicating as slight a difference as 0.1 cc, may 

 at once be restored by means of the resistance, so that irregularities 

 in the 0, supply, amounting to more than 0,1 cc. need not occur. 



The hydrogen simultaneously produced by the electrolysis in Z 

 is collected in the burette bii. After necessary corrections (in height 

 of barometer, tempeiature, water- vapour tension and pressure of 

 the water-column in the burette) the quantity of hydrogen received, 

 divided by 2, denotes the volume 0,, brought inio the ap|)aratus 

 during the observation. 



The nninometer ?/(, renders some other services. When a solution 

 of kalium-jodide (with some soluble amylum) is used, ?/(, is a 

 sensitive test for the existence of spores of ozon. In the presence 

 of this gas for instance the germ-plants of Pisum sativum do not 

 develop normally, so that it is desirable to prevent ozon from 

 entering the respiratory -apparatus. 



Finally we have in the manometer ??;, a suitable test whether 

 the desired temperature has been completely adopted by the whole 

 apparatus as well as by the objects. If the observations are started 

 before the whole has attained the desired temperature, the fluid 

 will at once rise in the open limb of m^, which signifies, that 

 extension still takes place, while in consequence of the respiration 

 (O, absorption) an immediate decrease of volume should appear. 



