THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 453 
Taking all these experiments together, in which the plants were shaded from rain and 
‘dust, but still allowed free access of air, the total gain of Nitrogen was 0:0192 gramme 
upon 0-2307 gramme supplied in the seed sown. There was a gain of Nitrogen, therefore, 
equal to about one-twelfth of that sown in the seed. Bovussineautt considered that 
part of the gain was due to organic corpuscles, and part to the ammonia im the atmo- 
sphere. He also considered that, bearing in mind the circumstances of the experiment, 
the gain was not sufficiently great to justify the conclusion that there had been any 
assimilation of the free or uncombined Nitrogen of the air. 
5. M. Boussincavt’s collateral experiments to control and explain his results*. 
In order to ascertain the amount of Nitrogen that might be introduced into the mate- 
rials under experiment when the matter used as soil, &c. was not excluded from the 
air whilst cooling after ignition, or when free access of air was allowed during the whole 
period of vegetation, BoussINGAULT instituted the following experiments. 
Sand, powdered brick, powdered bone-ash, and wood-charcoal were each exposed to the 
air for two or three days after being ignited, and then the Nitrogen determined in them. 
The result was that, after this exposure, a kilogramme of sand gave 0°5 milligramme, 
a kilogramme of powdered brick 0-5 milligramme, a kilogramme of powdered bone-ash 
0-84 milligramme, and a kilogramme of wood-charcoal 2°9 milligrammes of ammonia. 
In order to test the influence of the organic corpuscles of the atmosphere, a pot of 
burnt sand, with ashes, the whole moistened with water, was so arranged under a shade 
as nevertheless to allow free access of air, and it was so exposed for two and a half 
months. At the end of this period small spots of cryptogamic vegetation were visible 
on the surface of the sand; but the whole yielded only 0-74 milligramme of Nitrogen. 
Again, BoussincauLt found that unless the ashes used as manure were burnt until 
nearly all apparent traces of carbon were destroyed, they were liable to retain more or 
less and sometimes material amounts of Nitrogen. In some imperfectly burnt ashes 
cyanides, and in some, ferrocyanides were found; in others the Nitrogen seemed to exist 
in neither of these conditions. 
With regard to the much larger gain of Nitrogen indicated in his early experiments 
in free air (1837 and 1838) than in those made more recently, BoussineauLT remarks 
that. the result may be partly due to the comparatively defective methods of analysis at 
the early date, and. partly also to the distilled water used for watering the plants con- 
taining some ammonia. For, at the time of his first experiments, he was not aware of 
the fact, since learned in his analyses of rain and other waters, that water distilled 
from that which contained minute quantities of ammonia did not come over free from 
it until about two-fifths of the whole had been drawn off. 
It will be observed that, in most of the experiments of BoussincavLt thus far passed 
in review, he limited the supply of Nitrogen to the. plants to that contained in the seed 
sown, and to that which they could obtain from the atmosphere, either washed or un- 
* Ann, de. Chim. et de Phys. sér. 8. tome xliii, 1855. 
