192 SOIL CONDITIONS AND PLANT GROWTH 



soils, and by sewage beds. The observations go back to the 

 time when the sources of nitrogen for vegetation were being 

 investigated, and attempts were made to set up a balance 

 sheet showing the relation between the amounts of nitrogen 

 in the plant and the soil at the beginning and at the end 

 of its growth respectively. Reiset, 1 Ville (288^), and Boussin- 

 gault (45) sometimes found less nitrogen in soil + plant at 

 the end of an experiment than in soil + seed at the beginning, 

 and attributed the difference to an evolution of free nitrogen. 

 Some of these early observations were probably faulty by 

 reason of the crudeness of the analytical methods, but Lawes, 

 Gilbert, and Pugh (164) showed that loses of nitrogen un- 

 doubtedly took place sometimes, though not always, when 

 nitrogenous organic matter, wheat-meal, barley-meal, or bone- 

 meal, was made into an " agglutinated condition " with water, 

 and allowed to decompose in presence of air. Practically no 

 ammonia could be detected. Lawes and Gilbert suggested 

 three possible reactions, a suggestion that still holds the field. 



1. An oxidation analogous to that of the action of chlorine 

 on ammonia, by which free nitrogen is evolved. 



2. A reduction similar to that of a great number of sub- 

 stances upon the oxygen compounds of nitrogen, by which 

 the oxygen is appropriated and the nitrogen set free. 



3. These two actions may operate in succession the one 

 to the other. 



Little attention was paid to these results at the time, but 

 later on losses of nitrogen were found to occur in the purification 

 of water and of sewage. Angus Smith 2 in 1863 observed 

 an evolution of gaseous nitrogen from a dilute solution of 

 putrefying blood, and showed that nitrates gave off nitrogen 

 under certain circumstances. The earlier sewage workers, 

 Frankland, 3 and others, did not actually mention any loss of 



1 Reiset, Jahresbericht der Chemie, 1856. 



2 Angus Smith, Memoirs Manchester Lit. and Phil. Soc., 1863, 1867-8, Vol. 

 IV. ; also Report to the Local Govt. Board, 1882. 



3 Frankland, Denison, and Chalmers Morton, Royal Commission, Pollution 

 of Rivers, 1868, Vols. 1-4. 



