DENITIIIPICATION BY PURE CULTURES. 37 



EXERCISE XXVn. 



DENITRIFICATION BY PURE CULTURES OF DIFFERENT SPECIES. 



1. Place 50 cc. of the "Giltay" solution in each of eight 

 250 ee. Erienmeyer flasks. 



2. Plug and sterilize in the autoclave. 



3. Inoculate as follows : 



1 & 2 — sterile. 

 3 & 4 — Ps. pyocyaueus. 

 5 & 6 — B. denitrificans. 

 7 & 8— B. coli. 



4. Incubate for 7-8 days at 20° C. 



5. Divide each culture into three equal portions; deter- 



(a) Total nitrogen by digestion, according to the modified Kjeldalil 



method, 

 (i) Ammonia nitrogen by distillation with magnesium oxide, 

 (c) Nitrate and ammonia nitrogen according to the Ulsch method. 



The total less the ammonia and nitrate nitrogen equals 

 the organic nitrogen. The nitrogen found by the Ulsch 

 method less the ammonia nitrogen, equals the nitrate nitro- 

 gen. 



