BOTANY. 289 



first step towards the elucidation of the matter was made by Cloez 

 and Gratiolet, who, exposing the leaves of a common pond weed in 

 water, slightly impregnated with carbonic acid, found the first day 

 15.70 per cent, of the gas eliminated was nitrogen ; the second, 13.79 ; 

 the third, 12.00; the fourth, 10.26; the fifth, 9.53; the sixth, 8.15; 

 the 8th, 2.90. That is, the oxygen gas grew purer and purer, exactly 

 as if the azote retained in the tissues of the plant, or in the water, 

 was gradually expelled by the oxygen. Similar experiments were 

 made by Boussingault, in 1844, confirming these results ; and also, 

 later, a set of comparative experiments, with and without leaves, 

 which confirmed the truth of the conjecture as to the source of most 

 of the nitrogen. But, after all, he could not obtain any oxygen gas 

 free from azote. 



Boussingault now devised a new method of proceeding, by which 

 he avoided the difficulty about extraneous nitrogen, etc. The mean 

 results of twenty-five experiments, which are detailed particularly 

 in the memoir, made with a variety of plants, are, that 100 measures 

 of carbonic acid gas, decomposed by foliage under the light, give 97.2 

 of oxygen gas; and that 1.11 of azote had appeared, which, from the 

 plan of the experiments, could not have come from the water, nor 

 have been contained in the plant. 



At this point, Boussingault raised the question whether this gas, 

 which remained after the absorption of the oxygen by the pyrogailate 

 and the carbonic acid by potassa, was necessarily and really nitrogen. 

 A suite of experiments, devised and executed in this view, brought 

 out the interesting result that the supposed azote, which, moreover, 

 corresponded very nearly with the amount of oxygen gas that had 

 disappeared, was oxide of carbon, that is, carbonic oxide ! There is 

 also a little protocarburet of hydrogen. So, " foliage during the de- 

 composition of carbonic acid does not really emit nitrogen gas, but 

 with the oxygen gas emits some oxide of carbon and some protocar- 

 buret of hydrogen, and these combustible gases, like the oxygen, are 

 produced only under the light of the sun. . . . In other terms, to 

 keep strictly within the conditions of the experiments, these gases 

 constantly accompany the oxygen of which the sun determines the 

 production, when it acts upon a vegetable submerged in water im- 

 pregnated in carbonic acid." Is this also the case when carbonic 

 acid is decomposed by foliage in the air ? 



Boussingault concludes his paper with the remark, that the earlier 

 observers looked at their discoveries rather from the hygienic than 

 the physiological point of view ; that, while Priestly announced his 

 brilliant discovery by the statement that plants purify the air vitiated 

 by combustion or by the respiration of animals, it is curious enough 

 that a century afterwards it should come to be demonstrated, before 

 the Academy of Sciences, that probably the leaves of all plants, and 

 certainly those of aquatic plants, while emitting oxygen gas, which 

 ameliorates the atmosphere, also emit one of the most deleterious of 

 known gases, carbonic oxide ! He closes with the pregnant and nat- 

 ural query, whether the unhealthiuess of marshy districts is not attrib- 

 utable, at least in part, to the disengagement of this pernicious gas by 

 plants. 



We add, that what strikes us with most surprise, is to learn that if 

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