Evening star., 1936-12-31
BY THOMAS r. HENRY,
Stan CORRESPONDENT of The Star.

Stan Correspondent OF The Star.
ATLANTIC CITY, December 81
An instrument that measures instan-
taneously carbon dioxide concentra-
ton in air with a precision of one
part in a million, and which may prove
an invaluable tool in both pure SCI
ence and medicine, was described be-
fore a section meeting OF the Ameri-
can Association for the Advancement
Of Science here yesterday afternoon
hy DR.. E. D. McAllister of the Smith
sonian Institution.
The mechanism already has un-
locked the doors, 1t was reported. to
understanding of fundamental be-
havior Of plant growth which hitherto
had eluded all investigators, and
which is the foundation of all lie on
earth.
A possible future field of usefulness
will be in measuring human basal
metabolism. of extreme importance in
physical examinations, but which re-
quires a long time and is expensive.
With this device such examinations
can be made cheaply and in a few
minutes.
Basis Of Instrument.
The Instruments basis is the fact
that carbon dioxide Is opaque to a
certain narrow band of radiation in
the invisible infra-red spectrum. A
beam of this light is shot through q
quantity Of air. which one desires to
analyze. It fails to get through to
a degree corresponding to the num-
ber of carbon-dioxide molecules which
are encountered. That which does
get through falls upon a spectrograph
which is so arranged as to admit only
radiation of this particular wave
length. Behind the spectrograph is
a thermo couple, one Of the most deli
cate Of all radiation measuring de-
vices.
The radiation falling upon the ther-
mo couple sets up minute electric cur
rents in proportion to its intensity.
which are recorded on galvanometer.
It is so sensitive that as little as one
part Of carbon dioxide per million Of
air can be detected. The same pre-
cision could be reached by micro
chemical analysis, but it would re-
quire half hour or more, and pro-
crossing changes, of the utmost i'm
portance, could not be detected.
The instrument has far.reaching
implications in certain types of micro
chemical analysis, in the study Of
plant life and possibly in medicine.
The fundamental process of life on
earth, it often is stated, is photo
synthesis-the building up by cells
of plant of hydrocarbons out of water
absorbed through the roots and car
bon dionde absorbed by the leaves
from the air under the influence of
light. These hydrocarbons built up
by the plant are the basic food of ami
mails and the basic source of heat and
power obtained from combustion.
"Breathes" Carbon Dioxide.
The plant "breathes" carbon diox-
ide only in the presence of light. The
energy of the light quanta absorbed
enables the plant to combine the
carbon dioxide molecule with the
molecule of the green pigment Of its
leaves, chlorophyll. In darkness car
bon dioxide is exhaled only. The
plant, it might be said, falls into a
sort of sleep.
One of the most important findings
with the new instrument reported by
Mr.. McAllister deals with the Sleep
ing and waking habits" A plant
in most cases a wheat seedlings
placed in an air-tight chamber through
which precisely measured amounts OF
carbon dioxids in air can be sent.
First the specimen is kept in darkness
and the beam of invisible light shot
through the mixture. The galva-
nometer records an increase of the
gas at a constant rate, due to the
plants respiration. Then the light
is turned on. Almost instantly the
carbon dioxide begins to decrease as
its molecules are breathed in and
hooked on the chlorophyll molecules.
But after a nights sleep it requires
about 10 minutes for this decrease
to reach a maximum, constant rate.
In other words, it requires about 10
minutes for the plant to wake up
after q natural duration of darkness.
The length of the period decreases as
the period of darkness Is decreased.
Quite different Is the reverse proc
ess. The plant goes to sleep instantly
the light Is turned off-that is, the
carbon dioxide begins to increase.
The change has been noted in one
sixtieth of a second. Thus apparently
is solved a problem with which plant
Psychologists have wrestled for q long
time. A plant, it seems, is breathing
out carbon dioxide all the time at
q constant rate. and not Just when
it is asleep. Otherwise there would
be . transition period comparable to
that which accompanies waking"
The instrument, Mr.. McAllister ex-
plains, measures precisely the abb
sorption Of carbon dioxide under vari-
Gus intensities and wave bands Of
visible light, different degrees Of tenn
perature and different concentrations
Of carbon dioxide in the air. OF even
greater importance, 1t measures the
process continuously.
Measures Water Vapor Content.
BY use Of another tnfra-red wave
band it measures just as accurately
water vapor content Of the air.
It constitutes perhaps the quickest
and most accurate means Of chemical
analysis known for . limited f,eld Of
gas mixtures.
A hitherto unsuspected one-celled