310 Miscellaneous. 



came from the decomposition of carbonic acid gas. Theodore de 

 Saussure, nearly at the beginning of the present century, ascertained 

 the fact (which has since been often overlooked) that the volume of 

 oxygen gas produced was not quite equal to that of the carbonic acid 

 decomposed ; and also that nitrogen gas was always evolved, to an 

 amount about equal to that of the oxygen gas which had somehow 

 disappeared. He supposed that this nitrogen came from the sub- 

 stance of the plant — not considering, what is now obvious, that the 

 substance of the plant did not contain, and therefore could not have 

 furnished, anything like this quantity of nitrogen. 



In more recent times, Daubeny was unable to obtain from leaves 

 oxygen gas free from nitrogen ; and Draper states that he found the 

 astonishing amount of from 22 to 49 per cent, of the gas emitted 

 from the leaves of Pinus tceda and Poa annua to be nitrogen. The 

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

 and Gratiolet, who, exposing the leaves of a common Pond-weed 

 (Potamoffeton perfoliatus) in water slightly impregnated with car- 

 bonic acid, found that 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, 815 ; the seventh, 4"34; the 

 eighth, 2 "90 : that is, the oxygen gas grew purer and purer, exactly 

 as if the nitrogen 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 nitrogen. 



Boussingault now devised a new method of proceeding, by which 

 he avoided the difficulty about extraneous nitrogen, &c. The mean 

 results of 25 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, gave 97*2 

 of oxygen gas ; and that 1*11 of nitrogen 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 pyrogal- 

 late and the carbonic acid by potassa, was necessarily and really 

 nitrogen. A series of experiments, devised and executed with this 

 view, brought out the interesting result, that the supposed nitrogen 

 (which, moreover, corresponded very nearly with the amount of 

 oxygen gas that had disappeared) was oxide of carbon, i. e. carbonic 

 oxide ! There is also a little protocarburet of hydrogen. So " foliage, 

 during the decomposition of carbonic acid, does not really emit 

 nitrogen gas, but, with the oxygen gas, emits some oxide of carbon 

 and some protocarburet 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 experi- 



