368 



NA TURE 



{March 7, 1878 



at producing salpetre by artificial means. To Glauber, a 

 chemist of the seventeenth century, apparently belongs 

 the credit of first preparing nitre artificially. The process 

 as carried out in the present day is in outline as fol- 

 lows : — Soil, containing more or less of vegetable mould 

 and carbonate of calcium, is mixed with a certain pro- 

 portion of stable manure or other refuse animal matter, 

 and disposed in small heaps, care being taken that the 

 mass of soil and manure shall be sufficiently porous to 

 ensure the free admission of air : these heaps are pro- 

 tected from rain, and are from time to time watered with 

 stable sewage. At the end of two or three years the 

 earth is sufficiently rich in nitre to be worth extracting. 

 This tedious process for manufacturing nitre has, during 

 the last few years, been superseded to a considerable 

 extent by the treatment of Peruvian nitrate of sodium 

 with chloride of potassium, by which nitrate of potassium 

 and chloride of sodium are produced. 



It is evident that the artificial nitre-beds just described, 

 merely perform, on an exaggerated scale, an operation 

 which occurs naturally in all ordinary soils. The chemical 

 analysis of drainage waters has taught us that such waters 

 are characteristically rich in nitrates, and that the amount 

 of nitric acid present stands generally in close relation to 

 the quantity of nitrogenous manure previously applied to 

 the soil. The published analyses of the drainage waters 

 from the experimental wheat-field at Rothamsted, show 

 that ammonium salts applied as manure are rapidly con- 

 verted into nitrates by the soil, the quantity of nitric acid 

 in the drainage water being proportional to the amount of 

 ammonium salt applied. The recent application of soil 

 for the purification of sewage is another striking example 

 of the same action. The sewage, as poured upon the soil, 

 contains ammonia, and putrescible organic matter rich in 

 nitrogen ; the sewage which has filtered through a few 

 feet of porous soil is found to contain nitrates, but only 

 traces of orgamc nitrogen or ammonia. 

 . What explanation can we give of this phenomenon of 

 nitrification ? It is clearly a process in which nitrogen is 

 oxidised into nitric acid ; but how is this oxidation 

 brought about ? The old chemists believed that a decaying 

 organic body evolved more or less of its nitrogen in a free 

 state, and that this nitrogen, while nascent, combined with 

 the oxygen of the air to form nitric acid. This view has 

 been held by some down to the present day. Hofmann, 

 in his Exhibition Report of 1862, ofters the same 

 explanation, only substituting for free air the oxygen con- 

 densed on the surface of porous bodies. This theory has 

 been extended by some to include the ordinary nitrogen 

 of the atmosphere, so that on their view nitric acid may 

 be formed in soil from the nitrogen and oxygen of the 

 atmosphere, without the intervention of other nitrogenous 

 matter. According to others the oxidation of gaseous 

 nitrogen is brought about not by ordinary oxygen, but by 

 ozone. Other chemists have inclined to the belief that 

 nitrogen is never oxidised in the soil except when in the 

 form of ammonia, and that the nitrogen of organic 

 matter is always converted into ammonia as a preliminary 

 to nitrification. According to some experiments, the 

 ferric oxide, which gives a red colour to so many of our 

 soils, is itself an oxidising agent, and capable of convert- 

 ing ammonia into nitric acid. 



We need not, however, enumerate all the opinions that 

 have been held on this confessedly obscure subject. 

 Many of the experiments which were thought to support 

 certain views, now appear, in the light of recent evidence, 

 of little value. Before, however, discussing the new 

 facts recently contributed to the subject, we may just 

 indicate those points which have been most clearly 

 established. 



There is very little evidence for supposing that gaseous 

 nitrogen is ever converted into nitric acid in the soil. 

 Nitrous and nitric acid are indeed produced by electric 

 discharges through the atmosphere, thus originating the 



small amount of nitrates brought to the soil by rain, but 

 this appears to be the only reaction capable of producing 

 nitric acid from the direct union of oxygen and nitrogen. 

 According to Carius even ozone is quite incapable of 

 oxidising gaseous nitrogen. Ammonia is, on the other 

 hand, oxidised by ozone, nitric acid being formed ; but 

 that ozone is an agent in soil transformations is certainly 

 unproved, and appears very improbable. There remains 

 the action of ferric oxide, already referred to. This reac- 

 tion deserves further study ; it cannot, however, be con- 

 sidered as generally important, since nitrification certainly 

 occurs with vigour in soils practically destitute of ferric 

 oxide. 



The researches of successive generations of chemists 

 had thus failed to give any satisfactory explanation of the 

 important phenomenon of nitrification. The subject has 

 quite lately been attacked by Schloesing and Miintz from 

 an entirely new point of view ; their results, published in 

 the early part of last year, plainly indicate that nitrifica- 

 tion, instead of being brought about by purely chemical 

 forces is, in fact, the work of a living organism. The 

 evidence adduced in support of this new view is very 

 simple. These chemists show that nitrification, however 

 active, is immediately stopped by the vapour of chloro- 

 form, a substance which previous study has shown to 

 suspend the action of yeast, and of all organised ferments. 

 They also find that when nitrification has thus been sus- 

 pended for many weeks, it can be restarted by the addi- 

 tion of a small quantity of a nitrifying body. In a second 

 communication they further prove that the temperature 

 of boiling water is sufficient to destroy all power of nitri- 

 fication, and that soil which has been once heated to this 

 point produces, in air free from germs, carbonic acid and 

 ammonia, but no nitrates. If, however, this soil is moist- 

 ened with water containing a little unhealed soil, the 

 production of nitric acid again commences. 



This new theory of nitrification has been investigated 

 at Rothamsted with results completely confirmatory of 

 the views put forward by these French chemists. It was 

 found that the vapour of bisulphide of carbon, and of 

 chloroform, effectually prevented nitrification in a moist 

 garden soil through which air was frequently aspirated, 

 while without these vapours the soil produced nitrates in 

 considerable quantity. A solution of chloride of ammo- 

 nium containing a little tartaric acid, phosphate of potas- 

 sium, and carbonate of calcium, was also completely 

 nitrified in a few weeks by the addition of a small quan- 

 tity of soil taken from the " fairy-ring " of a meadow. 

 This solution, when nitrified, was successfully used as 

 seed to produce nitrification in other similar solutions, 

 which, without this addition, produced no nitric acid. It 

 was further shown that light was prejudicial to nitrifica- 

 tion ; solutions kept in a dark cupboard producing nitric 

 acid, while similar solutions standing in daylight produced 

 none. 



The evidence has thus become'very strong that the 

 nitrates in soil owe their origin to oxidation brought about 

 by living organisms. That mycoderms, in their processes 

 of life, may exert a powerful oxidising action upon organc 

 matter, we have already learnt through the researches of 

 Pasteur and others. The most familiar example is that 

 of the acetic fermentation. Vinegar is produced by the 

 oxidation of alcohol during the growth of a very simple 

 organism, the My coder 7na aceti , without the growth of 

 such an organism no vinegar is ever formed. It is by 

 similar low organisms that fermentation of all kinds is 

 brought about. Putrefaction has also been shown to be 

 equally dependent on the presence of microscopic orga- 

 nisms, and except under the conditions suitable for their 

 rapid development putrefaction will not take place. 

 With this abundant evidence before us of the energetic 

 decomposition of organic matter, brought about by what 

 we may term microscopic fungi, we can hardly be 

 astonished to find that the same agency is capable of 



