(il 



or whether any nitrous or nitric acids have heen produced. Theso pro- 

 cesses are of a purely chemical, technical nature, and therefore would 

 not be properly described in this place In the case of an active and 

 fertile soil, the nitrifying process begins promptly, and, as a rule, con- 

 tinues with unabated vigour until the whole of the nitrogen present in the 

 ammonium salt is converted into nitric acid. In very favourable circum- 

 stances this object will be accomplished in about six weeks. When the 

 organisms in the sample are few in number or deficient in vitality, the 

 nitrification does not begin for a long time, and then goes on with great 

 slowness. By tracing the progress of the fermentation, as described 

 above, it is seen how easy it is to compare various samples of soils in 

 respect of nitrifying power If after four or five weeks no trace of 

 notification has been found, the soils are regarded as being practically 

 deficient in nitrifying ferments. This often happens with samples taken 

 at a depth of three or more feet, or even in the case of surface soils or 

 others subjected to conditions inimical to fermentative life. 



REPRESENTATION OF THE DATA OBTAINED. 



In the actual work which has been done in this department to follow 

 the progress of nitrification in culture solutions it has been found con- 

 venient to determine the rate of the fermentative change by the deter- 

 mination of the nitrous and nitric acids produced. It is evident that in 

 the process of fermentation three cases may arise. In the first place, the 

 nitrous fermentation may occur first, and after its completion the nitric 

 may follow it. This is a condition which evidently would rarely arise, 

 and could only occur when the nitrous ferment was present in such a 

 predominating quantity as to subdue and restrain vitality of the 

 nitric ferment In the second place, the two fermentations could go on 

 synchronously, and in this case the solution when tested would never 

 contain more than the merest trace of nitrous acid. This condition of 

 affairs would only occur when the two ferments were present in about 

 equal numbers and endowed with equal vitality. In the third place and 

 this is the one which commonly occurs the two fermentations go on syn- 

 chronously, but at first the nitrous fermentation is more vigorous, so that 

 there may be a considerable accumulation of nitrous acid in the solution. 

 After a few weeks the nitric fermentation begins to gain in vitality by 

 reason of the fact that the raw material on which the nitrous ferment 

 worked has become nearly exhausted. The quantity of nitrous acid, 

 therefore, which was at first formed would gradually begin to disappear, 

 and finally, if the examination be continued long enough, be reduced to 

 zero at or before the time when the total amount of nitrogen present would 

 be converted into nitric acid. 



In order to represent the progress of the fermentation, it has been 

 found most convenient to use a graphic form * of illustration. The 

 method of doing this is illustrated in a chart showing the progress 

 of nitrification in a sample of soil taken a depth of 15 inches be- 

 low the surface, on the 27th of April, 1895, at the Canebrake station in 

 Alabama. The culture solution was seeded with a sample of this soil on 

 the 3rd of May, and the progress of nitrification is represented in the 

 chart. The figures in the perpendicular column on the left represents the 

 parts per million of nitrous or nitric acid. The continuous line represents 

 the sum of the nitrous and nitric acids. The dotted line represents the 



