SODIUM 



205 



of pulp separately using, alternately, the open and sealed ends of 

 the thin capillary tube in order to obtain a filter well packed on the 

 sides and in the center. Make the packed filters 0.6-0.8 mm. thick, 

 and see that no spaces are present around the filter mat. 



Fig. 76. Apparatus for determination of sodium. A and C are 

 approximately actual size. B is an enlargement (X20) of the 

 end of a filter tube. From Bott (1943) 



4. Wash and test the filters by filling the tubes, with the aid of a 

 syringe and adapter, with redistilled water. Place them in a round- 

 bottomed centrifuge tube fitted with a mat of clean dry filter paper 

 on the bottom, centrifuge for about 1 min., examine the tubes, and 

 discard any which have not drained completely. Dry the filter tubes 

 at 105° in a clean vessel and store in covered weighing bottles kept 

 in a dust-free container. 



