THE SOOCES OE THE XITBOGEX OF YEGETATIOX, 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 gam of Nitrogen, therefore, 

 equal to about one-twelfth of that sown in the seed. Boussixgault considered that 

 part of the gain was due to organic corpuscles, and part to the ammonia in 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. Boussixgaitlt'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, Boussixgault 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 

 0-8-i 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, Boussixgault found that unless the ashes vised 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 ; hi 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, Boussixgault 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 Boussixgault 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 China, et de Phys. ser. 3. tome sliii. 1855. 



