409 



the glass cock k, {k, is tlien closed) it reaches tlie absorptionlnbes 

 èj, b, and h,, containing baryta- water. On its waj' back tlie air 

 passes tiiroiigh the wash-flask (/,, containing sulfuric acid like d 

 and the control-baryla-tnbe c, after which it returns to p and 

 recommences its circular course. 



In a subsequent observation k^ is closed and k^ opened, causing 

 the CO, absorption to take place in the tubes b^, b^ and b^. The (> 

 absorption-tubes are fixed to a copper frame with clips. In order 

 to enable us to take more than two observations, without bringing 

 too many tubes in the glass vessel filled with water, which serves 

 as a thermostat, we should have two of these frames at our disposal. 

 If one has served its purpose, the connecting parts 1 and 2 are 

 turned up and rise above the water, where they may be loosened. 

 The whole frame with the 6 baryta-tubes is raised out of the vessel 

 and the other (the tubes of which are meanwhile cleaned and filled 

 each with 100 c.c. baryta-water) is put in. This exchange of frames 

 is brought about in less than a minute, but before taking further 

 observations with the newly-inserted baryta-tubes, we should wait 

 (according to the temperature in the thermostat) 10 — 15 mins. that 

 the tubes and their contents may adopt the temperature of the 

 thermostat. The apjuiratus works ventilating during this time in the 

 following way : Cock k, is closed, while k^ and /■, are opened. If 

 next the pump is set working, the air, leaving the vessel, can only 

 pass through k^, while at k^ air is sucked in, after having first 

 been rid of CO, by means of wash-flasks containing strong KOH- 

 sohitions (not represented in the fig.). There is another advantage 

 in the ventilating action of the apparatus. When in experiments of 

 long duration the observations are stopped in the evening, the 

 apparatus can continue to work ventilating the whole night. Conse- 

 quently the objects are not subject to oscillations of temperature 

 and the next morning the experiment may at once be continued by 

 opening k, and closing k^ and k^. In experiments, lasting 10 — 12 

 hours, it saves a great deal of time, to put the plants into the 

 apparatus the previous night, so that early in the morning the ex- 

 periments can begin at once. After the ventilation during the night 

 all CO, has been driven from the apparatus which may be demon- 

 strated by blind experiments. 



When the outer-air is shut from the apparatus, and the pump is 

 set working, there is immediately produced an effective pressure on 

 the vessel, while the manometer m,, indicates a reduction of pressure. 

 If next k^ is opened, the air pressed in the vessel is blown off. On 

 subsequent gradual closure of this cock, the pressure in the vessel 



