404 MR. R. RIGG ON THE EVOLUTION OF NITROGEN 



fixed law. At the same time, however, it is certain that nitrogen, whether appro- 

 priated or evolved, is apparently the most uniform, while oxygen assumes the cha- 

 racter of a most fluctuating and passive agent. 



Hence, then, if plants, taken as a whole, contain from three to four per cent, of 

 their weight of nitrogen, and if to this we add the indefinite quantity, so far as we 

 can comprehend, which is evolved during their growth, the question naturally arises, 

 From whence do plants draw this part of their substance, as well as the volume of ni- 

 trogen which they furnish to the atmosphere ? a question of the greatest importance 

 in the practical application of the subject, and one not wanting in interest as a part 

 of the inquiry into the chemical changes which occur during the growth of plants. 



The quantity of animal and vegetable matter which forms a part of all soils suitable 

 for the growth of plants, invariably containing nitrogen, furnishes us at once with 

 one source from whence they may derive a part, if not the whole, of this element, 

 which is either found in their constitution, or given oflf to the atmosphere during their 

 growth. Hence an accurate examination of these soils at different periods might 

 enable us to determine the question as to whether or not the earth supplied the whole 

 of the nitrogen which is employed in vegetable economy. But from the many diffi- 

 culties consequent upon accurately experimenting upon soils previous to and after 

 the production of any plants, and also tlie examination of the plants so produced, we 

 are not able by this mode of proceeding to obtain results in any degree satisfactory. 



In order to free myself from all doubt upon this point, and to ascertain whether 

 the atmosphere did or did not furnish any part, and if any what proportion, of the ni- 

 trogen which enters into the constitution of plants, I had recourse to the ultimate 

 analysis of seeds and young seedling plants. 



Some seeds I steeped in distilled water, and some in filtered Thames river water. 

 When they had absorbed a sufficient quantity of water to favour the first impulse of 

 germination, 1 spread them on glass or china plates, and kept them at temperatures 

 favourable to germination and vegetation, in a room where the only source of nitrogen 

 would be that which was supplied by the seed and the atmosphere. The quantity of 

 dry seed experimented upon varied from thirty to one thousand grains, which were ac- 

 curately weighed. These I allowed to germinate and grow, keeping them regularly 

 supplied with the respective kinds of water only; and that nothing might be lost by 

 the water carrying off any of the soluble parts of the difflerent seeds, that water which 

 was employed in steeping each kind of seed at the commencement was afterwards 

 used in watering the same. 



Some of the experiments I favoured so as to have them germinating and growing 

 quickly, and others slowly. Some of them were terminated at one stage of their 

 growth, and some at another; and some of them were allowed to vegetate as long as 

 the seeds appeared to afford them nourishment. At the end of each experiment the 

 whole mass was enveloped in very thin paper, and dried at a temperature varying from 

 100° to 1 10° Fahr., powdered, and afterwards allowed to acquire the hygrometric state 



