DESIGN  OF A SIMPLE PLANT EXPOSURE CHAMBER
   U.S.  DEPARTMENT OF  HEALTH, EDUCATION, AND WELFARE
                Public Health Service

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   DESIGN OF A  SIMPLE PLANT  EXPOSURE  CHAMBER
                            by
                      Walter W. Heck
                      John A. Dunning
                           and
                      Henry Johnson
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
                   Public Health Service
    Bureau of Disease Prevention and Environmental Control
           National Center for Air Pollution Control
                      Cincinnati, Ohio

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National Center for Air Pollution Control Publication APTD-68-6

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                                   ABSTRACT
      The chambers used in plant exposure studies at the National Center for Air
Pollution Control utilize a dynamic, negative-pressure, single-pass flow system
with uniformity of toxicant  flow, mixing,  and distribution in the chamber.  The
simple design, described herein, permits easy installation of numerous chambers
in a  single air-handling system while still permitting individual control of cham-
bers.
Key  Words:  Exposure,  Chamber, Plants, Air Pollution

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          DESIGN  OF A  SIMPLE  PLANT EXPOSURE  CHAMBER

                        PRINCIPLES OF  CHAMBER DESIGN

     The effects of phytotoxic air pollutants on vegetation have been studied in a
variety of exposure chambers.   Many early chambers were either closed-system
designs or small greenhouses redesigned for exposure studies.   Certain basic
design features of the chambers discussed in this paper have been reported.
     Ideal chamber design permits maintenance of natural environmental con-
ditions during plant exposures.  Good design can be achieved by closely following
design specifications that consider the plants to be  studied and the purpose  of the
research.  The most desirable flow characteristics, the toxicants to be used,
and the degree of environmental control desired are other important  consider-
ations.  Versatility combined with simplicity should be the overriding considera-
tion.
     Chambers  should be fabricated from materials having low adsorption
characteristics to avoid possible reactions with the interior of the chamber,
since such side reactions could produce injury not  directly related to the toxicant
being studied.  The chambers should be either easily cleanable or inexpensive,
so that they may be discarded and replaced.
     Dynamic air systems are superior to static air systems, and can be of a
negative- or positive-pressure type.  The negative systems, however, eliminates
the potential hazard of toxicant release into the area in which the exposure  cham-
ber is  situated.
     Toxicant and air must be well mixed before the exposure "atmosphere"
enters the exposure chamber.  Air movement in the chamber may be laminar or
turbulent,  but design for a laminar flow system is  exacting,  since the plants in
the chamber interrupt the laminar flow and cause a modified-turbulent flow.  A
turbulent flow system  (with essentially  instantaneous mixing with air already in
the exposure chamber) can be constructed rather simply.
     Air can be recycled on a percent basis or completely exhausted from the
system.   Recycled air can cause corrosion or  deposit particles on the  air-

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handling equipment, and substances in the air may interact with certain chemical



components of the air-handling equipment to form products capable of producing



abnormal plant injury.  A single-pass  system eliminates most of the problems



encountered with a recycling system and makes monitoring and control of



chamber levels  of specific toxicants easier.  The single-pass system also adds



to the simplicity of total design.





     Gases that are potentially phytotoxic should be added in a diluted form in



the intake duct.   The duct should be designed to aid in the mixing of air and



toxicant and should be capable of accommodating several toxicants at a level at



which they would normally interact no  more than under ambient conditions.





     Lines carrying the toxic  substances should be chemically inert and  heat



resistant to allow the use  of high-temperature liquids in the low-ppm vapor phase.



When toxicants readily adsorb on chamber materials,  lines and chambers should



be well cleaned  or changed before  other toxicants  are used.





     The degree of  environmental control depends on the basic purpose of the



experiment.   Chambers should be  usable outdoors, in greenhouses,  or as in-



serts into special plant-growth chambers.  Where chambers are used under



natural conditions, exposures  should be considered only on days conductive to



producing injury,  unless environmental variations are part of the  experiment.





     When comparisons are desired, most exposures  require environmental



control. Although greenhouse conditions often suffice,  lighting must be controlled



in most geographical locations for a planned program.  Close environmental



control can be obtained by the  use  of a special plenum on the inlet of each ex-



posure  chamber, by insertion  of the chamber into a plant growth chamber,  or



by inserting an exposure chamber  equipped with the special plenum into a plant



growth  chamber.




     Simplified construction and appropriate air-handling allow the use of a



number of chambers in parallel without reducing the utility of the  specific cham-



ber design.

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                     DESIGN  AND CONSTRUCTION DETAILS


      The type of chamber used in experiments for the past 3 years utilizes a
dynamic,  negative-pressure,  single-pass flow system. Flow,  toxicant mixing,
and air are uniform,  and several toxicants can be injected at once.  Simplicity of
design permits easy installation of numerous chambers in a single air-movement
system and individual control of chambers.  With minor modifications, these
exposure  chambers have been used in plant growth chambers to study effects of
pollution on vegetation under  rigid control of environmental conditions.  Cost
breakdown for these chambers is detailed in the appendix.

GENERAL CONSTRUCTION

      A bank of eight chambers  (Figures  1 and 2) was  constructed with a single

air-handling system.  Construction details for the two chamber sizes used
(Figure 3) are identical, and  flow characteristics and performance data are
similar.  The large chambers are  30 by  36 by 30 inches high.  For the sake of
brevity, only the smaller chambers, which are 24 by 24 by  30 inches in size, are

discussed here.

      Details  of construction are shown  in Figures 3 and 4.  The  chamber frame
is made of 3/4-inch-thick plywood.   Plywood ties at all corners join the front
and back.  The base is  made  of 1/2-inch-thick plywood. All joints are nailed
and glued, and wood surfaces are sanded and finished with several coats of
white gloss enamel.  A false  floor  of 1/4-inch pegboard that has been painted

on both sides is placed 6 inches from the bottom of the chamber.

      The frame is covered with J-mil Mylar* film attached with heavy cloth
tape.   The Mylar is wrapped  around the sides and back, and a separate  piece
placed on the top.  The plywood-frame door is also covered with Mylar.  Four
wood  strips are used to position the  door on the front frames, and a clamp is
centered  on each strip.  The  door gasket is fashioned from 3/8-inch-OD Tygon
plastic tubing with heat-fused ends.  This gasket has  good resiliency and has

lasted for several years.
*Mention of product or  company name does not constitute endorsement by  the
 Public Health Service  or the Department of Health, Education, and Welfare.

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ALUMINUM
  INLET
  PIPE
                                                    HIGH-PRESSURE
                                                      BLOWER
                                                    S.P.,  335 Off
        IrlLET HEADER
                                                            (21 18 by 18 by 1-

                                                                 CHARCOAL FILTER
\\AIR PLENUM

18 by 18 by 42
Figure  1.   Schematic showing general  orientation and  construction of exposure chambers
            in greenhouse.   (All dimensions  shown are  in inches.)

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                 Figure 2.  Exposure chamber set up in greenhouse.
      The basic chamber is fitted for specific attachments.  A 1/2-inch opening




is made in the upper front right-hand corner for the air inlet; a 3/4-inch opening



on the right side is available for sampling probes; a 1/4-inch opening at the



lower right rear provides for temperature-sensing elements; a 7/8-inch opening



in the rear on the lower right-hand side accommodates the air outlet; and just



below the latter, a 1/4-inch opening is provided for filling the wet-bulb pan.





AIR-HANDLING SYSTEM





      The air-handling system for chambers used in greenhouses  is detailed in



Figure 1.  A high-pressure blower on the exhaust side of the chambers maintains



4-inch negative static pressure in the exhaust header.  All headers are galvanized



downspout material,  and all joints are soldered and taped to reduce air leakage.



The system has a 3/4-inch-diameter exhaust duct with a gate valve and a calibra-



ted orifice plate, which  has pressure taps to control and measure airflow through



the chamber.  This  design maintains a negative pressure of  0. 1 to 0.2 inch of



water in the  exposure chambers at an airflow of 5 cfm (one change every 2 min-



ute s).




     Air  enters the chamber through a 1-1/4-inch-ID aluminum duct from an



inlet leader at a linear rate of approximately 600 feet per minute.  This high-

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                                           SIDE  ELEVATION
Figure 3.   Details  of exposure  chamber design.   (All dimensions shown are  in inches.)

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                      Figure A.   Greenhouse exposure  chamber
                                 detaiIs.

speed linear flow produces violent turbulence in the chamber and causes essen-

tially "instantaneous" mixing.  The air passes into the  bottom of the chamber

through the pegboard separator.  When all the chambers are  running, a single

chamber can be opened without upsetting the airflow in the remaining chambers

by closing a ball valve in the individual chamber inlet duct.  Air passes into the

inlet header through a cleaning plenum equipped with an initial dust filter and a

charcoal filter.  After the air is filtered,  it is  ozonated to remove reactive

substances; and then  it passes through a charcoal filter to remove the added

ozone.

     The air-handling system for controlled exposure has a 2-inch exhaust duct

with a damper and a calibrated orifice plate, which has pressure taps to control

and measure airflow  through the chamber.  The exposure chamber design and

air movement are the same as those for the greenhouse  system (Figures 5 and 6).

The inlet  system is modified so that each  chamber has an individual  inlet.  The

inlet duct connects to a special plenum, which is designed for close control of

temperature and humidity (Figures 7 and 8).   Air enters the plenum  through a

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                                                               DUCT-PASSAGE
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                                           CHAMBER
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                                                                                                   SIDE SECTION VIEW
                        Figure  5.   Schematic showing two exposure chambers  with  conditioning plenums inside a plant growth
                                   chamber, front and side views.   (All  dimensions  shown are in inches.)

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                      Figure 6.  Exposure  chamber  inserts in
                                 plant growth chamber.

charcoal filter (to which an ozonating device may be attached), then passes over

a set of heaters, through a steam humidifying unit, over the temperature-sensing

device that controls the heaters,  and into the inlet duct.  The control plenum and

inlet duct are well insulated with one-inch fiberglas insulating material.

TOXICANT ADDITIONS

      Toxicants are added through ports in the inlet duct from various toxicant

dispensing systems.   The dispensing systems have an initial dilution system, so

that toxicants enter the  inlet duct in concentrations of about 100 to  1.  A fluted

piece of aluminum foil within the duct above the point of toxicant addition gives

the air-toxicant mix a circular motion before it enters the exposure chamber.

Present inlet duct construction limits the number of toxicants that  can be added,

but a design  change will allow up to 10 different toxicants to be added and mixed

before entering the chamber.

ENVIRONMENTAL CONTROL

      Greenhouse exposure chambers are normally maintained at greenhouse

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          Figure 7.  Details of conditioning  plenum for exposure chambers
                     located within plant growth  chambers. (All  dimensions
                     shown are in inches.)

 conditions.  On a  cloudy day these conditions include low light,  low temperature,
 and high humidity.  On a sunny day a chamber receives about 80 percent of the
 light intensity of the greenhouse, is 4° to 6°F warmer, and has about the same
 humidity as the greenhouse.  All of the experiments with ozone and sulfur dioxide
 exposure at the National Center for Air Pollution Control have shown that supple-
 mental light is essential to obtain statistically significant results when parameters
10

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                  Figure 8.  Plenum attachment to exposure  chamber
                            inserts in  plant growth chamber.

other than light are considered.  An eight-lamp bank of 8-foot-long, 235-degree

reflector,  VHO lamps mounted on  a 2-inch aluminum angle frame with no top is

used.  Ballasts are mounted on the frame.  This bank covers three chambers and

gives 1800 to 2200 foot-candles of  light  in the  center of each chamber (Figures 9

and 10).  Airflow can be varied from 2 to  10 cfm through the small chambers and

from 5 to 20 cfm through the large chambers.

      The controlled-exposure chambers are mounted as inserts inside standard

plant growth chambers.  Inside dimensions of growth chambers currently in use

are 30 by 30 by 66 inches.  Each chamber permits  the use of two exposure  cham-

ber inserts.  Lights can be controlled to give intensities up to about 6, 000 foot-

candles.  Both incandescent and fluorescent lighting can be used; however,  the

incandescent generally has not been used because of the higher heat load.  Light

intensity in the two inserts in a given growth chamber can be varied by shading

one chamber with cheese cloth or another material.  Temperature,  humidity,

and toxicant are controlled independently in the  two exposure chamber inserts.

Temperature and  humidity are initially  controlled in the growth chamber, where

temperatures are maintained  at levels at least 10°F below the  lowest  insert

temperature desired and humidity  is kept as low as possible.  Air is conditioned

in each insert plenum for close control  of temperature and humidity within  the

exposure  chambers.  Airflow can be varied from 3 to 40 cfm through  each insert.

      Wet- and dry-bulb thermistors are situated in front of the  exhaust  duct in

each chamber to monitor temperature and humidity.
                                                                             11

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             ALUMINUM
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EXPOSURE
CHAMBER








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EXPOSURE
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EXPOSURE
CHAMBER








                                                                                             LAMP
                                                                                            'HOLDER
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    EXHAUST HEADER-
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                                           -FROM FILTER
                   -TO EXHAUST FAN
   N— WORK PLATFORM
' 5  IN FRONT OF CHAMBERS
   Figure  9.   Details  of supplemental  lighting  system for greenhouse exposure.
               (All  dimensions  shown are in inches.)

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Figure 10.   Details of lamp bank over greenhouse
            exposure chambers.
                                                                13

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                               PERFORMANCE DATA

     The value of any instrument is measured by its performance under actual
operating conditions.  The principal concern with the exposure chambers dis-
cussed here is maintaining uniform toxicant and environmental conditions through-
out the chamber, and the ability to maintain consistent values over a given period
of time.   The former is an indirect indication of chamber flow characteristics
and the latter is a measure of the stability of the toxicant dispensing and en-
vironmental control systems.
     To determine the operating performance of the exposure chambers dis-
cussed,  ozone was used as a test toxicant.  The chambers were checked empty,
with a plant load,  and at several ozone concentrations.  Ozone was chosen for
several reasons, but the prime consideration was its  reactive nature.   If ozone
mixing is at an acceptable level,  other toxicants should show an equal  or better
distribution pattern.
     Preliminary measurement of toxicant uniformity was made shortly after
the small chamber system was  completed.  Variations within the chamber were
less than ±4 percent both empty and with a plant load.  Chamber concentrations
were compared with inlet levels and expressed as percentage values.  Empty
chamber values  were close to inlet values; loaded chamber values ranged from
as low as 50 percent to as high  as nearly  100 percent of inlet values.   The per-
centage values of loaded chambers seemed to be related to plant sensitivity.  On
days of high sensitivity, a probe held  against the lower leaf surface of tobacco
or pinto bean plants within the chamber showed a value of as low as 20 to 30 per-
cent of the inlet value.  Much of the ozone reduction is possibly due to absorption
into leaf tissues.  This is currently being investigated.
     Environmental conditions  similar to those found in greenhouses exist within
greenhouse exposure chambers.  Under bright  sunlight, the chamber temperatures
run from 4° to 6°F above greenhouse  temperatures at an airflow rate  of one
change every 2 minutes.  Measurements at several points within the chamber
have been markedly consistent.
                                                                             15

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      Environmental control is particularly important within exposure chamber
 inserts to plant growth chambers.  A preliminary design similar to the one here-
 in discussed,  was set up to determine what was necessary for close temperature
 and humidity control.  At an airflow rate of 20 cfm with two changes per minute,
 there was less than ±0. 5°F temperature fluctuation at a given level in the cham-
 ber.  Difference in temperature between top and bottom of chambers  was approxi-
 mately 2°F at a chamber temperature of 70°F.   This was  a consistent variation.
 At higher temperatures the difference was less.  At any given location no tempera-
 ture or humidity variations could be picked up by using a wet-bulb,  dry-bulb
 thermistor sensing device.
      A more detailed measurement of ozone uniformity in both the  large and
 small greenhouse exposure chambers was  recently conducted (Table 1).  Four

         Table 1.  UNIFORMITY  OF  OZONE  DISTRIBUTION  IN  EXPOSURE CHAMBERS3
Chamber and conditions
Large chamber, empty, no per-
forated delivery tube
Large chamber, empty, with
perforated delivery tube
Large chamber, light plant load,
with perforated delivery tube
Small chamber, empty
Small chamber, light plant load
No. of
runs
9
4
5
3
2
Chamber positions"
A
100
97
100
98
100
B
97
99
97
100
98
C
92
95
96
96
98
D
93
100
96
97
100
E
93
97
89
97
100
 aThe values were obtained as comparative values for a given  run, and then all values
  in a run were compared, the highest  value being given the arbitrary value of 100.
  This was done because of variations  between runs.
  Positions A-D were located 2 inches  from the corners at the vertical center!ine of
  the chamber.  Position A at the inlet corner and the other  positions occurring
  counter clockwise around the chamber.  Position E was centrally located at the
  same height as the other positions.
probes were centered vertically in each chamber within 2 inches of the four
corners (A-D); and a fifth probe was placed in the center of each chamber (E).
Results for each probe location were originally calculated  on the basis of the per-
centage of the inlet concentration.  Results of ozone uniformity for the different
runs varied so much, because of environmental conditions and chamber loading,
that all values were corrected so that the highest value would read 100 (Table 1).
16

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The large chambers were checked empty both with and without a perforated
delivery tube installed.  (The inlet duct was connected to a 1-1/4-inch Plexiglas
tube extending across the inside of the chamber.   This tube had eight 1/4-inch
holes for more uniform dispersion of air across the chamber. ) Results show
more uniform dispersion with the tube added.   The  ozone uniformity level at the
center of the chamber was definitely below that at the four chamber corners when
the chamber was tested under plant load conditions.  This is probably a plant
response.  The  perforated tube was not used in the small chambers, and no cham-
ber center effect was noted.  Results show excellent uniformity of mixing within
chambers of both sizes.
      Determination of the rate  of chamber equilibration after  starting  or stopping
toxicant flow into the chambers is also of  interest. The rates  of equilibration for
ozone were determined for all five probe positions for both chamber sizes.  Aver-
age values for the five probe positions are shown for the large chambers in Figure
11.  Results for the small chambers were similar.  The equilibration rate after
starting the dispensing system and the decay rate after stopping the dispensing
system are the  same.   Thus, the length of the exposure can be determined by
knowing the time of starting and stopping the dispensing system.  The time period
for equilibration is so short that for runs  of one or more hours, the lower con-
centrations during  equilibration and decay should not have a. major effect on plant
response.   The  lower concentration during the equilibration and decay time
periods  could have an effect on plant response for exposure  periods under one
hour.  The shorter the exposure period the greater effect these lag periods would
have.
                                    SUMMARY
      The construction details of a simple, flexible plant exposure chamber have
been described.  The chamber utilizes a dynamic, negative-pressure, single-
pass flow system,  which provides uniformity of flow, toxicant mixing, and cham-
ber distribution.  Environmental control of exposure inserts into plant growth
chambers  can be maintained with no apparent light, temperature,  or humidity
fluctuations.  Chamber uniformity of ozone concentration is excellent, and
uniformity of less  labile  toxicants should be greater.
                                                                              17

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                                         EQUILIBRATION   OZONE  ADDITION
                                               EQUILIBRATION   OZONE REMOVAL _
                      234567

                                TIME TO EQUILIBRIUM, minutes
10     11    12
          Figure 11.  Rate of  equilibration and removal of  ozone for large
                      chambers  (average of 5 probe positions).
18

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                            ACKNOWLEDGEMENTS

     We would like to thank Mr. A. R.  Schwarberg of the Health Effects Research
Program, National Center for Air  Pollution Control,  for the schematic drawings
in Figures 1, 3, 5, 7 and 9; and, Dr. O. C.  Taylor of the Air Pollution Research
Center, University of California, Riverside, California, for suggested changes
in design as the result of use of this system at Riverside.
                                  REFERENCES

1.  Heck, W.  W. , E. G.  Pires,  and W. C. Hall.  The effect of a low ethylene
    concentration on the growth of cotton.  JAPCA.  11:549-556. 1961.
2.  Heck, W.  W. and E. G. Pires.  Growth of plants fumigated with  saturated
    and unsaturated hydrocarbon gases and their derivatives.  Texas  Agric.
    Exptl. Station.  MP-603.  1962.
3.  Heck, W.  W. , L. S. Bird, M.  E. Bloodworth,  W. J. Clark, D.  R. Darling,
    and M. B. Porter.  Environmental pollution by missile propellents.  MRL-
    TDR-62-38.  Office of Technical Services.  Dept. of Commerce.   1962.
                                                                             19

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              APPENDIX





CONSTRUCTION COSTS FOR EXPOSURE FACILITIES

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                                   APPENDIX
CONSTRUCTION COSTS FOR EXPOSURE FACILITIES
1.  Construction of an eight-exposure chamber setup for use in the greenhouse.
    (Figure 1)
          1 gallon of white enamel paint                               $  8. 00
          2 charcoal panel filters,  18 by 18 by 1-inch @ $7. 00            14. 00
          4 sheets of 3/4-inch plywood, @ $8. 00 (4- by 8-foot sheet)      32. 00
          1 sheet of 1/4-inch pegboard (4-  by  8-foot sheet)                5. 00
          100 feet of 3/8-inch-OD Tygon* tubing  for  gasketing and
            connections                                                10.00
          32 toggle clamps.   No.  205-U DeStaCo, @$1.80               58.00
          1 Dayton high-pressure blower,  530 cfrn,  1-inch static         54.00
          60 feet of 5-inch round  downspout, $3. 12/10 feet              20. 00
          8 calibrated orifice plates adapted to 3/4-inch copper
            tubing,  estimate $30.00 each                              240.00
          24 feet of 1-1/2-inch-OD aluminum  tubing                     14. 00
          20 feet of 3/4-inch-OD  copper tubing                           4. 00
          1 roll of 1-mil clear Mylar film                               10. 00
          1 roll Mystic tape                                             5. 00
          8 ball valves,  1 1/4-inch @ $9.00                             72.00
          8 gate valves, 3/4-inch No. 607  Hammond, @$3.11            25.00
          1 inclined manometer,  3-inch Meriam Inst. No. 40GE4        50. 00
          8 wet-bulb containers,  @ $5. 00                                40.00
          Labor for construction, covering, setup, and installation     300. 00
                                    i
                                                                      $961.00
2.  Construction of a single exposure chamber without connections.  (Figure 3)
          Paint                                                       $  1-0°
          Plywood                                                      4- °°
          Pegboard                                                      •60
          Tygon tubing                                                   • 40
          Toggle clamps                                                7- 40
*Mention of a trade name or  company is for identification only and does not imply
  endorsement by the USDHEW.
                                                                              23

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           Mylar film                                                 $   1. 00
           Mystic tape                                                     . 60
           Wet-bulb container                                            5. 00
           Construction and covering                                     25. 00
                                                                        45.00
 3.   Construction of a single 8-foot supplemental lighting system for greenhouse
       exposure chambers.  (Figure 9)
           8 sockets, No.  492 and 493  Levitron, @ $2.40                $ 19.20
           25 feet of 2- by 2- by 3/16-inch aluminum angle                25. 00
           8 fluorescent tubes,  FR96T12/CWVHO-235-1,  g $5. 75         46.00
           4 ballasts,  GE No.  7G1201,  @$27.75                         111.00
           Labor:  construction, wiring, etc.                             25. 00
                                                                      $226.20
 4.   Construction of a single exposure chamber insert for use in a plant growth
     chamber.   (Figure  5)
           Chamber construction (#2)                                  $ 45. 00
           2-inch round  downspout                                        1. 00
           Conditioning plenum (#5)                                      87.00
           Calibrated orifice plates adapted to 2-inch copper tubing       30. 00
           Insulation                                                     4. 00
           Installation                                                   50.00
                                                                      $217. 00
 5.   Construction of a single conditioning plenum.  (Figure 7)
           Sheet metal                                                 $  5. 00
           4-1/2-inch diameter charcoal canister filter                   14.00
           2 heaters, strip, @ $5.65                                     11.00
           Thermostat for heaters, Chromalox AR-2534                  22.00
           Steam connection with needle valve                            10. 00
           Construction                                                 25.00
                                                                      $ 87.00
24

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