January 1948 &-739
United States Department of Arriculture
Agricultural Research Awcir.' tation
Bureau of Entomology and Plant Quarantine
CARBON DIOXIDE AS A PROPELLENT FOR i...iC[LE SOLUTIONS(
By R. A. Fulton,
Division of Insecticide Investigations
The liquefied-gas aerosols in common use contain approximately 80
percent of Freon-12 (dichlorodifluoromethane) as the propellent, and
usually 2 percent of pyrethrum extract (containing 20 percent of pyreth-
rins) and 3 percent of DDT. They are formulated for the treatment of
enclosed spaces, and leave no appreciable deposit of DDT on ceilings and
vertical surfaces. However, if the percentage of nonvolatile material
in the aerosol is increased by the addition of acetone or other organic
solvents, a coarse mist is produced which will adhere to all types of
surfaces. The liquefied gas Freon-12 has a vapor pressure of approxi-
mately 85 pounds per square inch (gage) at room temperature. When the
content of nonvolatile materials is increased to 50 percent, the pres-
sure is reduced approximately one half, or to 40 pounds per squrze inch.
This reduced pressure is insufficient to carry the particles more than
24 inches. A study has therefore been made of the use of carbon dioxide
to increase the pressure of the solution and thus make the mist effective
for greater distances, and to decrease the cost of the solution by re-
ducing the Freon content. Tests are now being conducted in greenhouses,
on field crops, and on treated surfaces in the laboratory to determine
the advantages and disadvantages of this method of applying organic in-
A number of formulas, in which carbon dioxide has been added to
various solvents and organic insecticides, have been tested to determine
the most effective combination for the particular type of surface being
treated. Two typical formulas are as follows (figures in percent):
Component G-496 G--470
DDT (aerosol grade) 10 9.5
Cyclohexanone 10 -
Velsicol AR-60 ,(chiefly di- and
tri-methylnaphthalenes) 10 9.5
Acetone 65 28.6
Methylene chloride technicala) 47.6
Freon-12 5 4.8
Carbon dioxide is added to bring the pressure to 150 pounds per
l/ A portion of this research was conducted as part of a projr'm
supported by a transfer of funds from the Office of Qu rteoanster Genoer.-l,
U. S. Arny, to the Bureau of Entomology and Plant Qu&rantine.
Formula G-496 leaves an oily deposit on nonabsorbent surfaces, but
on foliage and other absorbent surfaces the deposit soon becomes white.
The deposit from formula G-470 is white soon after the droplets contact
any type of surface.
Formula G-496 absorbs 13.6 grams of carbon dioxide per 100 grns of
solution, whereas G-470 absorbs only 7 grams. If a solution is discharged
on a weight basis, a correction must be made for the increase in weight
due to the absorbed carbon dioxide.
The carbon dioxide-propelled insecticide solutions are prepared in
the malirer described for the Freon-12 types (Goodhue and Sullivan 1,
Fulton et al. 2), except for the addition of the carbon dioxide. The
container is washed with dry acetone and evacuated. The DDT is dissolved
in the solvernts and filtered, and the weighed solution is then drawn into
the container through a copper-tube connection. The container is con-
nectcd to the Freon-12 supply, filled with the desired weight of the liq-
uefied gas and then connected to a liquid carbon dioxide tank equipped
with a reducing valve and gage. The valve is set for 180 pounds per square
inch pressure. The gas is allowed to bubble through the solution by
holding the container in an inverted position. As considerable heat is
generated within the container while it is being filled with carbon dioxide,
it is necessary to cool it in water at approximately 65 F. The reducing
valve is then set for 150 pounds, and as soon as the container has cooled
it is shAken until no more gas passes through the reducing valve. The
container is then ready to be connected to an oil-burner nozzle for use.
Ti-.e delivery rates of the two formulas through different-sized noz-
zles are shown in table 1. The rate of flow for formula G-496 is constant,
whereas for formula G-470 it decreases approximately 10 percent v.hile the
container is being emptied.
Table 1.--Discharge rates and amount of DDT deposited by two solutions
containing carbon dioxide as propellent, when discharged through oil-
burner nozzles of different sizes.
Size of Rate of discharge IDT deposit
nozzle L (Grams per second) (Milligrams er square foot
(Gallons Der Formula G-496 Formula 0-470 Formula G-496 Formula G-470
1.35 1.15 1.26 45 42
1.65 1.62 1.73 52 47
2.00 1.80 2.00 70 65
2.50 2.27 2.33 71 71
3.00 2.51 2,53 4 79
4.00 3.12 3.33 112 105
5.00 3.6 4#26 155 140
When carbon dioxide is used as the principal propellent, the rapid
drop in pressure is eliminated by the addition of a small percentage of
The deposits of DDT obtained on glass plates suspended apprcxiictely
16 inches from the oil-burner nozzles are also shown in table 1. The
container was moved at the rate of 1 foot per second, at vrhich rate there
was no dripping on the glass surfaces.
Carbon dioxide appears to be a satisfactory propellent for iinsecti-
cide solutions containing DDT. The characteristics of the mists produced
are such that they may be used as space sprays or as residual sprays for
protection against crawling insects. Preliminary field tests against the
pea aphid indicate that solutions propelled with carbon dioxide are more
efficient than those depending entirely upon Freon-12 or methyl chloride.
(1) Goodhue, L. D., and Sullivan, W. W.
1942. The preparation of insecticidal aerosols by the use of liq-
uefied gases. U. S. Bur. Ent. and Plant Quar. ET-190,
3 pp. [Processed.]
(2) Fulton, R. A., Berlin, F. D., and Bochert, R. S., Jr.
1947. A laboratory method for filling aerosol containers. U. S.
Bur. Ent. and Plant Quar. ET-245, 2 pp. [Processed.]
UNIVERSITY OF FLORIDA
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