CH. II] GAS ANALYSIS. 37 



KHO. The apparatus is now exposed to bright diffused 

 light for 5 or 6 hours, or it may be exposed to sunlight. 

 When the exposure to light is complete the leaf must be 

 pulled out by the wire, and when the apparatus has cooled, 

 readings are again taken. 



In order to estimate the quantity of CO2 which has 

 been decomposed, about 0"2 or 0'3c.c. of concentrated 

 KHO is injected into the gas-tube; this Pfeffer recom- 

 mends to be done by the heat of the hand acting on a 

 closed pipette. After 2 hours the CO2 may be assumed 

 to be all absorbed, when readings are again to be taken. 

 The volume of the leaf is also to be ascertained by 

 sinking it in a narrow measuring glass and reading off 

 the altered position of the level ; the fluid may be a 

 mixture of alcohol and water which prevents adhesion 

 of bubbles to the leaf The volume of the leaf being 

 known it must be applied as a correction to the readings 

 of the gas-volume. To obtain the result it is necessary to 

 reduce the readings of the calibrated tube (before and 

 after the injection of KHO) to 0°C. and to 1 meter 

 mercury pressure, and to make allowance for water vapour 

 tension, etc. This is to be done according to the formula 

 of Bunsen^ 



1 „ _ fc-m) (6-61-62) 



1 1 + 0-00366*° ■ 

 Where »!= the reduced volume of gas. 



V =the observed volume. 

 m=the correction for meniscus. 

 6 =the barometric reading. 

 6i=the mercury pressm-e in the eudiometer. 

 62= the water -vapour tension at the temperature t°. 

 See Bunsen and Eosooe, Gasometric Analysis. 



