Source of Nitrogen 209 



contemporary scientists. It was soon demonstrated 

 by investigations on the Continent and in England that 

 the quantities of ammonia and of other nitrogen com- 

 pounds in the air are very small, and that the amounts 

 brought down in the rain and snow would account for 

 only a small fraction of the nitrogen removed in the 

 crops. Notwithstanding these investigations, Liebig 

 retained his belief in the sufficiency of the nitrogen 

 compounds in the air for supporting vegetation. 



Other theories. — To Boussingault in France and to 

 Lawes and Gilbert in England the facts then known 

 seemed to point in one direction. They had become con- 

 vinced that the nitrogen compounds of the atmosphere 

 were sufficient only for a very meager vegetation, 

 but there was still a possibility that the enormous 

 quantities of the free nitrogen of the air may supply 

 the needs of plants for this element. Accordingly a 

 series of experiments was instituted by Boussingault 

 in 1851, and by Lawes, Gilbert and Pugh in 1857. 

 These experiments were carried out with great care. 

 Determinations were made of the nitrogen in the seed 

 and soil at the beginning of the experiments and in the 

 plants and soil at their conclusion. 



Lawes, Gilbert and Pugh took the precaution to 

 calcine the soil employed, and to remove all the ammonia 

 from the air before it was admitted into the glass cage 

 where the plants were growing. Their results and those 

 of Boussingault agreed fully, all of them indicating that 

 the free nitrogen of the air was not available to the 

 plants in their experiments. These results were accepted 

 as decisive for many years, notwithstanding the ex- 



