326 GASOMETRIC-VOLUMETRIC METHODS 



placed on the bottom of the vessel, or the absorbent may be placed 

 in the loop and the sample on the bottom. 



An index drop of 2% Turgitol, or other wetting agent, is intro- 

 duced through the compensation chamber with a hypodermic needle. 

 Then a drop of water is placed in the compensation chamber, and 

 finally the opening is greased and sealed with a fiat piece of glass. 

 The instrument is operated in a manner similar to that employed 

 with the larger apparatus. 



2. Gas Analysis 



(a) Scholander Micrometer Burette Gas Analyzer 



Scholander (1942b) employed his micrometer burette to develop 

 an apparatus by means of which 10 /xl. of a gas mixture may be 

 analyzed for its various components with an accuracy of about 

 0.1% of the total sample. Specific absorbents for each component 

 are used, and the volume change resulting from the absorption of 

 each gas is measured. 



Apparatus. The apparatus is shown in Figure 101 (available 

 from 0. Hebel, Edward Martin Biological Laboratory, Swarthmore 

 College) . The micrometer spindle is replaced by a ^/le in. drill rod 

 (2) , which displaces about 50 /xl. by its full traverse. Each microm- 

 eter scale division corresponds to approximately 0.02 /xl. and esti- 

 mates are safely made to 0.005 /xl. The capillary bore is around 0.25 

 mm. and the bulb (3) has a capacity of about 50 /xl. The absorption 

 chamber (1) has a bore no greater than 2.5 mm. The fine line (4) is 

 used for reading. The drill rod must fit perfectly tight through a 

 fiber washer (5) and the mercury vessel must be completely freed 

 from air. The waterjacket surrounding the burette is clamped so 

 that it can be tilted by the handle (6) . 



Scholander uses separate 2 ml. syringes to hold the respective 

 liquids required, i.e., mercury, a manometer liquid of 2% Turgitol 

 (wetting agent), 0.5 N sulfuric acid, and gas absorbents such as 

 0.25 A'' potassium hydroxide which has been shaken well with air 

 (for carbon dioxide) and hydrosulfite (for oxygen). (The latter is 

 prepared by adding a mixture of 10 parts hydrosulfite and 1 part 

 sodium anthraquinone-/?-sulfonate to a small test tube filled with 

 0.25 N potassium hydroxide, containing a drop of mercury for mix- 



