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51
and is in air-tight isolation from the assimilation-chamber, The faste-
ning of the object on to the rod can be performed when the chamber is
either open or closed. In the former case the rod should be in the
position I. In the latter case it is drawn out to the posilion II. The
outer stopper is then loosened and allowed to slip out to the handle,
Ill. The leaf is attached to the rod and pushed into the tube,
whereupon the stopper (r,) is restored to its place. The withdrawal
or inserlion ofthe object from or into the closed assimilation-chamber
has the great advantage that immediately after the conclusion of one
experiment another can be begun with the same leaf in another
chamber. If the stopper r, is provided with two tubes, air can be
sucked through the glass tube and thus the respiration carbon dioxide
produced by the leaf may be gotrid of, and if necessary measured,
immediately before or after an assimilation experiment. The inner
stopper should then of course be drawn out (positions II and III).
The estimation of the carbon dioxide is performed by the in-
troduclion of a certain quantity of diluted baryta solution into the
bottom of the assimilation chamber by means of a glass bowl (b)
secured with paraffin. Through tube Tis introduced a glass tube
f, of equal calibre, reaching down to the bottom of the bowl. The
tube is closed on the outside by a short indiarubber tube and a
glass stopper. The baryta is sucked from a vessel of supply into
a pipette of 15 ccm. capacity, which is introduced into the mouth
of tube T, and then the baryta is allowed to run into the bowl and
spread itself uniformly over the bottom. Afterwards the tube is
closed, and the whole is left to stand as long as is necessary for
complete absorption (with 3, baryta and normal carbon dioxide per-
centage in the air, at least half an hour).
Then the baryta is sucked out into a small wide-necked flask of
50—100 ccm. capacity (IV). A quantity of water free of CO, is
introduced through tube T, and the bowl is rinsed out by gentle
shaking of the apparatus. The rinsing-waler is sucked up into the
same flask as the baryta, the process is repeated once or twice, and
litration then takes place directly into the flask with 3, oxalic acid.
The filling of the apparatus with ordinary air is most easily
effected by letting it stand in the open air for some minutes, with
the lid off, preferably in a windy place. The Ecological Station
offers ideal conditions in regard to fresh and constantly circulating
air. As the composition of the air by the sea remains very nearly
constant as long as the same wind is blowing, I only had to make
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