SODIUM AND POTASSIUM ( COMBINED) 267 



PROCEDURE 



I. Transfer sample of tissue containing 1 X 10"^, to 4 X 10~^ 

 milliequivalent of the alkalis into the bottom of a quartz tube. If 

 necessary, about 8 ix\. water can be placed in the tube to receive the 

 tissue. 



2. Add about 10 ix\. ashing reagent with the simple hand pipette 

 and place in an oven at 106° to evaporate the water. 



3. When dry, place in the incineration oven at 440-460° for 30 

 min. The grayish-white ash may contain dark particles of carbon, 

 but these do not influence the analysis. 



4. Add 100 ^1. distilled water to the ash with a calibrated con- 

 striction pipette, and stir carefully with a thin glass rod ( 1-2 mm. 

 diameter. 



5. Cap the tube and centrifuge for 5 min. at 2000 R.P.M. 



6. Draw off 70-80 fA. of the supernatant with a calibrated 

 constriction pipette and transfer to a glass reaction tube of the 

 usual type (page 166). 



7. Add 15 ju.1. precipitation reagent with another standardized 

 constriction pipette and introduce a stirring "flea." 



8. Cap the tube and let stand 2 hr., stirring the mixture from time 

 to time; then remove the "flea" with the electromagnet. 



9. Centrifuge as before and transfer 70-80 lA. supernatant to a 

 quartz tube using the same pipette as previously. 



10. Evaporate the water at 106° and incinerate for 1 hr. at 360°. 



II. Add 50 ix\. titration medium and titrate the chloride with the 

 silver nitrate soln. using the electrometric procedure (page 282). 



12. Run control experiments, omitting the sample, to obtain a 

 correction for alkalis in the reagents; the titration value of these 

 control runs should not exceed 0.2 /xl. silver nitrate soln. 



13. Standardize the silver nitrate soln. by carrying a known 

 quantity of pure potassium chloride through the steps in the 

 procedure. 



note: If in the above procedure it is assumed that pipettes having a 

 capacity of 101.1, 73.0, and 15.2 n\., respectively, were employed the calcula- 

 tion becomes: 



101.1 X 88.2 



Original content = titration value X 



73.0 X 73.0 



