June 9, 1892] 



NATURE 



37 



Experiments on Continuous Nitrification in Mineral Solutions. 



The separation from these foreign forms was ultimately 

 effected by enormously diluting one of these nitrifying solutions, 

 and then taking out small portions of this diluted material and 

 introducing each of these portions into separate ammoniacal 

 solutions. In some of these nitrification was established, in 

 others not, whilst amongst those in which nitrification 7uas 

 established, some contained organisms which grew upon gelatin, 

 whilst one refused to give any growth on the gelatin at all, 

 although it was seen under the microscope to contain abundantly 

 bacteria of the form shown in the diagram. [Lantern-slide of 

 nitrifying bacillococcus (Frankland).] 



These results, which were published in March 1890, were fol- 

 lowed in about a month by a communication in the Annales de 

 VInstitut 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 nitrons 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) NH3 -1-30 = HjO -f NHO, 

 (Ammonia) (0.\ygen) (Water) (Nitrous Acid) 



(2) NHOo + O = NHO3 

 (Nitrous Acid) (Nitric Acid) 



The organisms separated by Winogradsky, by Warington, 

 and by myself, possessed only the property of effecting 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. 

 [Demonstration 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 oxidizes to nitrate. 



NO. II 80, VOL. 46] 



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

 one of the most powerful oxidizing 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 hoiv 

 then is the nitric acid found in the soil produced, when 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: (i) that 

 nitrous and nitric acids are priduced 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. 



More recent researches of Winogradsky have shown that the 

 first of these two alternative hypotheses is the correct one, for, by 

 making cultivations of soil in a solution containing nitrous acid 

 and no ammonia, Winogradsky has succeeded in isolating a 

 micro-organism which possesses the power of converting nitrous 

 acid into nitric acid, but has no power of attacking ammonia. 

 [Lantern-slide of nitric ferment (Winogradsky).] 



This second organism or nitric ferment, as we may call it, 

 resembles in its activity the purely chemical oxidiziuii agent — 

 potassium permanganate — which, as we have seen, has no action 

 on ammonia, but readily converts nitrous into nitric acid. 



The process of nitrification in the soil now becomes intelligible 

 in its entirety. It is the work of two independent organisms, 

 the first of which converts ammonia into nitrous acid, whilst the 

 second transforms into nitric acid the nitrous acid produced by 

 the first. 



There is a point in connection with the distribution of nitric 

 acid in nature which is exceedingly remarkable, and which forces 

 itself upon the attention of every student of the process of nitri- 

 fication. Although nitric acid is generally so scantily present 

 in the soil, there is one notable exception to this rule, for in the 

 rainless districts of Chili and Peru there are found immense de- 

 posits of nitrate of soda, or Chili--altpetre, as it is called, whijh 

 would appear to represent the result of a gigantic nitrification 

 process in some previous period of the earth's history. The vast 

 quantities of this material which occur in these regions of South 

 America can he gathered from the fact that its exportation has 

 for years been going oti at the rate indicated by the following 

 figures:— During the first six months of 1890 there were brought 

 to the United Kingdom 90,000 tons, and to the European con- 

 tinent 480,000 tons. 



From the presence of such altogether enormous quantities, 

 one is almost tempted to hazard the suggestion that in this par- 

 ticular region of the earth, under some special circumstances of 

 which we know nothing, the nitrifying organisms must have been 

 endowed then and there with very much greater powers than 

 they possess to-day, and it is particularly noteworthy that in a 

 recent examination of soils from nearly all parts of the earth, 

 one coming from Quito, and therefore not far distant from these 

 nitrate fields, was found to possess the power of nitrification in a 

 degree far beyond that exhibited by any other soil hitherto ex- 

 perimented with. Is it not possible, perhaps, that we have in 

 these vigorous nitrifying organisms of the soil of Quito, the not 

 altogether unworthy descendants of the Cyclopean race of nitri- 

 fying bacteria, which must have built up the nitrate wealth of 

 Chili and Peru, and thus countless ages ago founded the fortunes 

 of our nitrate kings of to-day ? 



But these nitrl^ing organisms have also assisted in teaching 

 us a highly important lesson in connection with the mainten- 

 ance of life. 



The facts which I have already referred to concerning the 

 multiplication of micro-organisms in distilled water, and the 

 continuation of the nitrification-process over a period of four 

 years iu purely mineral solutions, are strong presumptive evidence 

 in favour of these bacteria being able to gain a livelihood in the 

 entire absence of organic food-stuffs. I refrained, however, 

 from promulgating such a revolutionary doctrine until I should 

 have had an opportunity of repeating these experiments with 

 materials in which the absence of even the merest traces of 

 organic matter had been assured, for, as chemists well know, 

 even distilled water may contain traces of organic matter. 



Such a rigid proof as I had contemplated has, however, in the 



