Lerts & Bhaxke—The Carbonic Anhydride of the Atmosphere. 187 
One paragraph, however, in his pamphlet, “Die Beschaffen- 
heit der Waldluft ” is of peculiar interest. 
“To obtain a complete insight into the nature of forest air, it 
is necessary that the air should be examined during the time of 
vegetation, not only over the ground but also annORE the leafy tree 
crowns on clear and dull days.” 
“‘ In the Karsten forest, in a plantation of sixty-year-old pine- 
trees, several experiments were conducted in such a way that a 
leaden tube was attached to a tree 25 metres high, reaching from 
the bottom to the middle of the crown. The lower end was attached 
to a baryta tube, and 10 iitres of the ‘crown’ air were drawn 
by an aspirator through the baryta. There resulted, however, in 
these experiments always so little carbonic anhydride, that possibly 
some of it combined, during its long passage through the tube 
with the lead which had become moist. ‘Therefore I shall not 
regard the result of these troublesome determinations as decisive, 
but propose to repeat them in such a way that the baryta tube, 
shall be fastened within the tree crown, and a large quantity of 
air aspirated from below. At the same time I propose to examine 
the ‘ crown ’ air for its content of oxygen.” 
Uniortunately, however, we can find no account of the results 
of these proposed experiments which would have been of very 
great interest, in view of the fact that there is such slight experi- 
mental evidence of any definite effect of vegetation in reducing 
the amount of atmospheric carbonic anhydride. 
The want of this evidence is very probably due to the fact 
that all the observers have experimented close to the surface of 
the ground, and as a consequence their results have been affected 
by ground air. 
Lhe following considerations have occurred to us and may he of 
‘interest :—- 
Assuming that 1 square metre of leaf surface decomposes 1 
litre of carbonic anhydride per hour,' and also assuming that air 
contains 3°3 part of the gas per 10,000, the litre is contained in 
an.air space 1 square metre in area, and 3 metres high. A tree 
1 Ostwald (“* Outlines of General Chemistry,’’ 1890) gives 0°000,000,0537 grm. as 
the amount of starch formed, according to Pfeffer, by one square centimetre of oleander 
leaf per second, which corresponds with an absorption of about 1°6 litres of carbonic 
anhydride per hour for each square metre of leaf surface. 
SCIENT. PROC. R.D.S., VOL. IX., PART II. 1 
