9 



proved by the fact that whereas the filtrate from the soil receiving no 

 nitrogen contained on the average 0.72 gramme of nitric nitrogen, that 

 fn in the pots which contained horse-dung showed only 0.15 gramme of 

 the same foru of nitrogen. On other pots similarly treated mustard 

 was grown, the yield being much reduced by the addition of horse-dung 

 to the soil, whether with or without nitrate of soda. 



In another set of experiments Wagner put 2 kilogrammes of soil 

 into a series ot basins, to all of which he added nitrate of soda containing 

 nitrogen varying by 5 gramme from 0.2 to 1.4 gramme per basin. Cer- 

 tain of the basins received no dung, while others were supplied with 200 

 grammes and 400 grammes of this sub lance, holding I and 2 grammes 

 of nitrogen respectively. The experiment lasted for sixteen days, at the 

 end of which time the soil was extracted with water, and the amount of 

 nitrate of soda that remained unaltered was determined. As a result it 

 was found that where no dung was used practically the whole of the 

 nitrogen of the nitrate of soda was recovered in an unaltered condition, 

 but where horse-dung was present in the soil much of the nitric- 

 nitrogen had disappeared, the percentage disappearance being, as was to 

 be expected, greatest (a) where least nitrate of soda had been used, and 

 (b) in the presence of the large application of dung. Taking the aver- 

 age results, it was found that where the smaller amount of dung was used 

 the nitrate of soda had been reduced to the extent of 26 per cent., while 

 nearly 51 per cent, had disappeared under the influence of the larger 

 dressing. 



Row does Dung cause Waste of Nitrogen ? 



It now becomes of interest to ascertain what becomes of the nitro- 

 gen that loses its nitric form in the presence of dung. Does it take the 

 form of some insoluble compound, or of ammonia, or of free nitrogen ? 

 This part of the subject has been dealt with by Wagner, Maercker, 

 Stutzer, Pfeiffer, Dietzell, and others, and it has been conclusively shown 

 that the nitrogen is dissipated in the elementary form, and, of course, 

 escapes into the air. The method adopted to determine this point is a 

 very simple one, and consists in placing a given quantity ot nitrate of 

 soda and dung in a flask of convenient size, through which air is 

 drawn by means of an air pump. Before entering the flask the air is 

 passed through sulphuric acid in order to get rid of any traces of ammo- 

 nia, and similarly the escaping air and gases are passed through sul- 

 phuric acid of known strength. At the end of the experiment the loss 

 of nitrogen is determined, and the difference between such loss and the 

 ammonia produced may fairly be taken U represent free nitrogen. In 

 every case it has been found that the nitrogen has been liberated in the 

 elementary form, and that such liberation proceeds quite as actively 

 when a constant stream of air is drawn through the mixture as when 

 no such artificial air-circulation is secured. If air is altogether excluded 

 denitrification ceases, and it is hindered more or less in proportion to the 

 amount of aeration; but the free natural circulation of air would appear 

 to create as favourable denitrifying conditions as are secured by more 

 rapid and perfect artificial aeration. 



That the denitrification and liberation of free nitrogen is due to the 



