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excellently adapted to this end. The objection usually raised against
this principle, namely that the object of experiment is exposed to a
continuously falling CO, tension, is of little importance, provided that
care is taken that the amount of CO, absorbed is small in relation to
the total amount ofCO,. Parallel experiments with my method and
the aspirator method with absorption in a PETTENKOFER tube have
given similar values for the assimilation! (see e. g. Table I, nos. 12
and 13, Table VIII, nos. 10 and 11, Table IX, nos. 6 and 7).
When one has to work with the extraordinarily small quantities
of CO, present in the air, the methods of analysis used by Prerren,
BONNIER and MANGIN, and others are not sufficiently exact. Nor
are the gas-analysis apparatuses constructed for different purposes
by PETTERSSON (1897), KroGH (1908) etc. — though very good in
themselves — suitable for estimations of assimilation in the small
CO, pressure of the air. The apparatus constructed by me, which
combines assimilation-chamber and absorption-room, is arranged as
follows.
The apparatus has the form of a round, open box of zinc, with
double walls. The space between the walls is filled with water by
means of the tube (D, the temperature of the water is shown by a
thermometer. As lid (I) I use a piece of looking-glass, 2—5 mm.
thick, which rests on a raised edge 1 cm. broad, smeared with
vaseline, and is made to seal the vessel hermetically by means of
metal clamps with springs (cl). The dimensions are so chosen that
the volume of air enclosed measures 3 litres. The outer walls of
the box push up a little above the lid of looking-glass: when this
is set on, one can therefore pour water on to a space 2 cm. deep,
which is of great advantage for assimilation in sunlight. By means
of simple arrangements the water can be renewed continually. In
this way over-heating is entirely avoided. The thick envelope of
water round the box moreover remains, during an experiment lasting
1 hour, more or less at so constant a temperature that no special
heating and regulating arrangements are necessary, provided that
the temperature of the water is about the same as that of the sur-
rounding air. If required, the outer walls can be covered with some
heat-isolating material. The raising or lowering of the envelope of
water to the desired temperature is effected most simply by means
of a supply of hot or cold water in the tube (f), the outlet taking
1 My method however gives on an average somewhat higher values, a fact w hich
is probably due to the more complete CO, absorption.
4. — Svensk Botanisk Tidskrift 1921.
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