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ganisms which transform carbonate of ammonia into nitrous acid. Each 

 genus is necessary in the complete transformation of proteid matter 

 into nitric acid, in which latter form alone nitrogen is chiefly available 

 for plant food. 



FORMATION OF AMMONIA. 



The bacteria which are especially active in the formation of ammonia 

 are found constantly in surface soils and in the air and rain-water. By 

 the activity of these organisms in the decomposition of albumen or of an 

 albuminoid body, large quantities of ammonium carbonate are produced. 

 The organic carbon, which is present in the compound, is also acted 

 upon during the decomposition of the albumen, and by its oxidation cer- 

 tain organic acids are produced, together with carbon dioxide. Any 

 organic sulphur which is present in the original compound becomes con- 

 verted into an acid. As a rule, nitrogen in the decomposition of albumen 

 and albuminoid bodies is not produced in its free state unless, indeed, 

 the de-nitrifying organisms should attack the products of the first oxida- 

 tion. The ammonia ferment naturally produces alkalinity in the media 

 in which it is active, but it has been found that its activity is not wholly 

 destroyed even in the presence of a slight excess of acid, provided the 

 amount of acid present does not exceed one per cent As with the case of 

 the other nitrifying organisms, the ammonia ferment is most active in a 

 warm environment. A temperature of from 80 deg. to 100 deg. F. is 

 found most favourable to the production of a maximum fermentative 

 activity. As the temperature approaches the freezing point the aotivity 

 of the organisms diminishes and finally ceases altogether, but their 

 vitality is not destroyed. Above a temperature of 110 deg. F. the activity 

 of the ferment is also much diminished, and at higher temperatures 

 ceases. A temperature near the boiling point of water continued for some 

 time destroys the vitality of the organisms altogether. 



The demonstration of the fact that the transformation of organic 

 nitrogenous matter into ammonia is due to micro organic activity is 

 easily made in the following simple manner : Two samples of the same 

 soil are placed in suitable vessels. The percentages of ammonia and of 

 oxidised nitrogen which these samples contain are determined by the 

 usual chemical process. One of the samples is then sterilised by heating 

 it for a few hours to a temperature considerably above the boiling point 

 of water. After the lapse of a few weeks or months, the ammonia, or 

 its oxidised products, nitrous and nitric acids, is again determined in the 

 two samples. In the unsterilised sample it will be found, provided the 

 soils be kept moist and at the proper temperature, that there is a marked 

 increase of ammonia. In the sterilised sample no such increase will be 

 found. 



In general, it mav be said that the organic matter in the soil which 

 is the source of the ammonia is not altogether albuminoid or proteid 

 matter, but includes also the nitrogenous constituents of humus. Soil 

 humus is remarkably rich in carbon, and under the conditions favourable 

 to nitrification this is constantly suffering oxidation. As a result of 

 this constant oxidation, the percentage of carbon in humus maintained 

 for a long while under cultivation is much less in proportion to the other 

 constituents of that body than in soils which are regularly fertilised 

 with organic matters or in virgin soils. 



