On the Application of Manures. 



249 



other. In this manner, when the jar came to be placed over them, 

 and to dip beneath the sm'face of the mercury, the external air 

 was as effectually excluded as when the whole of the plant had 

 been enclosed. 



The results of several experiments, conducted after this plan, 

 are given in a tabular form in the Memoir ; but it may be suffi- 

 cient here to specify one of the most satisfactory of those under- 

 taken. In this case the jar itself contained about 600 cubic 

 inches of air, and the plant experimented on was the common 

 lilac (Syringa vulgaris). The proportion of carbonic acid in the 

 jar was each morning made equivalent to 5 or 6 per cent, by 

 additions through the tube. 



The first day no. great alteration in the air was detected, but 

 on the second day, by eight in the evening, the oxygen had risen 

 to 26 • 5 per cent. In the morning it had sunk to 26 • 0, but bj 

 two P.M. it had again risen to no less than 29*75, and by sunset 

 it had reached 30*0 percent. At night it sunk J percent.; 

 but the effect during the following day was not estimated, as the 

 sickly appearance w hich the plant now began to assume induced 

 me to suspend the experiment. 



In a second trial, however, the branch of a healthy lilac, grow- 

 ing in the garden, was introduced into the same jar, where it was 

 suffered to remain until its leaves became entirely withered. 



The first day the increase of oxygen in the jar was no more 

 than 0*25 per cent., but on the second it rose to 25 '0. At night 

 it sunk to nearly 22-0 percent., but the next evening it had 

 again risen to 27 " 0. This was the maximum of its increase, for 

 at night it sunk to 26 ♦ 0, and in the morning exhibited signs of 

 incipient decay. Accordingly, in the evening the oxygen amounted 

 only to 26 • 5 ; the next evening to 25 • 5 ; the following one to 

 24 • 75 ; and the one next succeeding it had fallen to the point at 

 which it stood at the commencement, or to 21-0 per cent. 



The reason of this decrease was, however, very manifest from 

 the decay and falling off of the leaves ; so that this circumstance 

 does not invalidate the conclusion which the preceding experi- 

 ments concur in establishing- — namely, that in fine weather, a 

 plant, so long at least as it continues healthy, adds consi- 

 derably to the oxygen of the air when carbonic acid is freely 

 supplied. 



In the last instance quoted, the exposed surface of all the 

 leaves enclosed-in the jar, which were about fifty in number, was 

 calculated at not more than 300 square inches, and yet there 

 must have been added to the air of the jar as much as 26-0 cubic 

 inches of oxygen, in consequence of the action of this surface upon 

 the carbonic acid introduced. 



But there is reason to believe that, even under the circum- 



