624 Professor Percy F. FranJcland [Feb. 19, 



contain abundantly bacteria of the form sliown in the diagram. 

 [Lantern-slide of Nitrifying Bacillococcus (Frankland).] 



These results, which were published in March 1890, were followed 

 in about a month by a communication in the ' Annales de I'lnstitut 

 Pasteur,' by M. Winogradsky, who had also separated a very similar, 

 if not identical, nitrifying organism, and a few months later, again a 

 similar separation was made by Mr. Warington. 



But these discoveries had not completely unravelled the problem 

 of nitrification, for the organisms separated in these three independent 

 investigations possessed only the property of converting ammonia into 

 nitrous and not into nitric acid. The nitrous acid is an intermediate 

 body which curiously is rarely found excepting in very minute 

 quantities in soil. The changes will be more clearly understood by 

 reference to the chemical equations : — 



(1) NHg + 30 = H^O + NHO. 



(Ammonia) (Oxygen) (Water) (Nitrous Acid) 



(2) NHO2 + = NHO3 



(Nitrous Acid) (Nitric Acid) 



The organisms separated by Winogradsky, by Warington, and by 

 myself, possessed only the property of efi"ecting the first of these 

 changes, they were absolutely destitute of the power of bringing 

 about the second. 



Now the curious thing is that the first of these changes is by far 

 the most difficult to accomplish by purely chemical means, whilst the 

 second can be brought about with the greatest facility. [Demonstra- 

 tion of addition of acid permanganate to solution of ammonium 

 sulphate, colour not discharged.] [Demonstration of addition of 

 acid permanganate to solution of potassium nitrite, colour discharged.] 



Thus the potassium permanganate has no action on the ammonia, 

 whilst the nitrite it oxidises to nitrate. 



In order to bring about the first change, we have to employ one 

 of the most powerful oxidising agents known to chemists, viz. ozone. 

 [Demonstration : ozone from a Siemens-tube was passed through 

 strong solution of ammonia; the production of nitrous and nitric 

 acids was exhibited by the formation of white fumes, as well as by 

 the sulphanilic acid and diphenylamine tests.] 



We thus see that the power of oxidation possessed by our nitrifying 

 organism is altogether unique, and does not find its parallel amongst 

 purely chemical agents of oxidation. But lioiv then is the nitric acid 

 found in the soil produced, ichen these organisms yield only nitrous 

 acid ? 



At the time when I found that the organism which I had separated 

 produced nitrous acid exclusively, I pointed out that it was doubtless 

 explicable on one of two hypotheses : (1) that nitrous and nitric acids 

 are produced by totally distinct organisms ; or (2) that the same 

 organism produces the one or the other according to the conditions 

 under which it is growing. 



