CSi REPORT— 1884. 



which amides or albuminoids were employed, the formation of ammonia preceded 

 the production of nitric acid. 



As ammonia is so readily nitrifiable, we may safely assert that every nitrogen- 

 ous substance which yields ammonia when acted on by the organisms present in soil 

 is also nitrifiable. 



Certain Conditions having Great Influence on the Process of Nitrification.— If we 

 suppose that a solution containing a nitritiable substance is supplied witli the 

 nitrifying organism, and with the various food-constituents necessary for its growth 

 :and activity, the rapidity of nitrification will depend on a variety of circumstances: — 

 i(l) The degree of concentration of the solution is important. Nitrification always 

 commences lirst in the weakest solution, and there is probably in the case of every 

 solution a limit of concentration beyond which nitrification is impossible. (2) The 

 temperature has great influence. Nitrification proceeds far more rapidly in summer 

 than in winter. (3) The presence or absence of light is important. Nitrification 

 is most rapid in darkness ; and in the case of solutions, exposure to strong light 

 may cause nitrification to cease altogether. (4) The presence of oxygen is of course 

 •essential. A thin layer of solution will nitrify sooner than a deep layer, owing to 

 the larger proportion of oxygen available. The influence of depth of fluid is most 

 conspicuous in the case of strong solutions. (5) The quantity of nitrifying organism 

 present has also a marked effect. A solution seeded with a very small amount of 

 organism will for a long time exhibit no nitrification, the organism being (unlike 

 some other bacteria) of very slow growth. A solution receiving an abundant supply 

 of the ferment will exhibit speedy nitrification, and strong solutions may by this 

 means be successfully nitrified, which with small seediugs would prove very refrac- 

 tory. The speedy nitrification which occurs in soil (far more speedy than in experi- 

 ments in solutions under any conditions yet tried) is probably owing to the great 

 mass of nitrifying organism which soil contains, and to the thinness of the liquid 

 layer which covers the soil particles. (G) The rapidity of nitrification also depends 

 ■on the degree of alkalinity of the solution. Nitrification will not take place in an 

 acid solution, it is essential that some base should be present with which the nitric 

 .acid may combine ; when all available base is used up nitrification ceases. It ap- 

 peared of interest to ascertain to what extent nitrification would proceed in a dilute 

 solution of urine without the addition of any substance save the nitrifying ferment. 

 As urea is converted into ammonium carbonate in the first stage of the action of the 

 ferment, a supply of salifiable base would at first be present, but would gradually 

 be consumed. The result of the experiment showed that only one-half the quantity 

 of nitric acid was formed in the simple urine solution, as in similar solutions con- 

 taining calcium and sodium carbonate. The nitrification of the urine had evidently 

 proceeded till the whole of the ammonium had been changed into ammonium 

 citrate, and the action had then ceased. This fact is of practical importance. 

 Sewage will be thoroughly nitrified only when a suflicient supply of calcium car- 

 bonate, or some other base, is available. If instead of calcium carbonate a sol- 

 uble alkaline salt is present, the quantity must be small, or nitrification will be 

 seriously hindered. Sodium carbonate begins to have a retarding influence on the 

 commencement of nitrification when its amount exceeds 300 milligrammes per litre, 

 and up to the present time I have been unable to produce an effective nitrification 

 in solutions containing T000 gramme per litre. Sodium hydrogen carbonate hin- 

 ders far less the commencement of nitrification. Ammonium carbonate, when above 

 & certain amount, also prevents the commencement of nitrification. The strongest 

 solution in which nitrification has at present commenced contained ammonium 

 carbonate equivalent to 368 milligrammes of nitrogen per litre. This hindrance of 

 nitrificatiou by the presence of an excess of ammonium carbonate effectually pre- 

 vents the nitrification of strong solutions of urine, in which, as already mentioned, 

 ammonium carbonate is the first product of fermentation. Far stronger solutions 

 of ammonium chloride can be nitrified than of ammonium carbonate, if the solution 

 of the former salt is supplied with calcium carbonate. Nitrification has in fact 

 commenced in chloride of ammonium solutions containing more than two grammes 

 of nitrogen per litre. 



The details of the recent experiments, some of the results of which we have 



