146 SOIL BACTERIOLOGY 



colorless. If sugar is absent, about two to three hours is 

 sufficient for complete digestion. 



6. In case the contents of the flask are likely to become 

 solid before digestion is complete, cool, and add 10 c.c. 

 more of sulphuric acid. 



7. When digestion is complete, cool, and add 200 c.c. 

 of water. Shake until the mixture is thoroughly in solution. 

 Be sure that none of the digested material remains caked 

 to the sides of the Kjeldahl flask. 



8. Recool, add a teaspoonful of powdered pumice to 

 prevent bumping, and shake thoroughly. 



9. Add 100 c.c., or more if necessary, of a saturated so- 

 dium hydroxid solution. (The stock solution of alkali 

 should be prepared two days or more before it is to be used 

 in order that the sodium carbonate may precipitate out. 

 Avoid the deposit in the bottom of the alkali.) Enough 

 alkali should be added to make the solution react strongly 

 alkaline. A few strips of litmus-paper may be added in 

 order to test the reaction. The alkali should be poured 

 slowly down the sides of the flask. After about half of the 

 alkali is added, it is well to shake the solution. Now add 

 the remaining alkali and connect at once to the condenser. 



10. See that the rubber stopper fits snugly in the flask. 

 Now mix the contents thoroughly by shaking. 



n. Just before connecting the flask have a very low 

 flame burning on the distillation shelf. After the alkali 

 and acid mixture are well mixed, raise the flame. 



12. The proper amount of standard acid should be 

 measured into flasks connected to the distillation shelf 

 prior to adding the alkali. 



13. Distil slowly. After the first fifteen minutes the 

 flame may be raised, but never so high that the distillate 

 collects in the condensing bulbs. Generally the first two- 



