LIBRARY ULIBR ARY -245
STATE PiL eqD STATE PLANT BOARD
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantiie
A LABOEATORT METHOD FOR KILLING AXWOL CONTAINERS
R. A. Fulton, P. D. Berlinoand R. S. Bochert, Jr.
DiTvision of Insecticide Investigations
The filling of containers with liquefied-gas aerosols for expert-
mental purposes has always presented certain difficulties, chief among
which are inaccuracies in weighing and contamination by moisture. The
contamination of hexaethyl tetraphosphate aerosols by moisture may
lead to serious corrosion problems and the formation of solid particles
which will clog the nozzles. An accurate laboratory method has been
developed which overcomes these difficulties and i' suitable for fill-
ing all sizes of containers and for all types of s andard formulas.
Most of the liquefied-gas aerosols in use contain Freon-12 (di-
chlorodifluoromethane) as the propellent. This liquid boils at -21.70
FP. (-29.5' C0) and has a gage pressure of 6704 pounds per square inch
at 68* F. (20' C.). Methyl chloride, which is used in the hexaethyl
tetraphoBophate aerosols, boils at -10.7' F. (-23.7 C.) and has a gage
pressure of 56.32 pounds per square inch at 690 F. (20 C.0). Methyl
chloride is not suitable, safe, or recommended for use in general-
purpose aerosols and should be used only where due precautions are
taken to protect the operator.
The predetermined amounts of pyrethrum extract, DDT, or other in-
secticides plus any solvents needed are first weighed, and the solution
is warmed, if necessary, to dissolve all the material. The container
to be filled is washed several times with acetone. Many of the refill-
able containers have a 1/8-inch brass pipe plug in the bottom for use
in cleaning and filling. The 5-pound containers are washed by evacuation,
drawing in 200 to 300 ml. of dry acetone, and shaking. The acetoneis
then removed by connecting the valve to a compressed-air supply and forcing
the acetone from the container under pressure. This process is repeated
until the acetone from the container is clear. The container is then
dipped in hot water and connected to a vacuum pump for 30 minutes. A
short length of copper tubing with a flared fitting is attached to the
evacuated container. The wvreighed solution containing the insecticide
and solvent is then drawn in. Care must be taken not to admit air,
because this will increase the initial presEure of the system and after
a portion of the aerosol has been dispensed the pressure will drop,
thus decreasing the rate of flow of the aerosol through the nozzle.
When many bombs are being filled with the same formula, the equip-
ment shown in figure 1 is used. The aerosol concentrate is placed in
the reservoir (A). The measuring flask (B) is calibrated for the solu-
tion being used. To prevent moisture from being absorbed by the solu-
tion, calcium chloride tubes (C) are placed in the stoppers of both the
reservoir and the measuring flask.
To fill the aerosol container (not shown) the aerosol concentrate
is first measured in flask j. The dried container is then evacuated
and connected to the copper tube from the measuring flask by means of a
refrigeration quick coupler (DP). The contents are slowly drawn into the
container. When the liquid is near the bottom of the flask, care must be
taken to avoid air being drawn into the container. The container is then
disconnec-t.d and placed on the balance for the filling operation. .
The filling apparatus shown in figure 2 was designed to eliminate the
possibility of injiu-' fr;jm the escaping propellent liquefied gas at the
end of the operation. Electric solenoid valves insure positive cutting
off of the liquefied gas when the desired amount has been measured into the
After the concentrate has been added, the aerosol container (a) is
placed on the balance (H) and connected to the flexible refrigeration hose
(Z) with the container valve closed. Solenoid valve C is then opened by
turning the switch at E to fill the system, including the hose, with the
propellent. The container is then weighed, and additional weights
equivalent to the amount of propellent to be added are placed on the
The propellent reservoir (A) is then heated with the steam jacket
(B) and the valve on the aerosol container is opened to allow the propellent
to flow in. The container is under partial vacuum, and until the natural
boiling point of the propellent is reached there will be a pronowiuced cooling
of the container. Wlien the desired amount has been added, the switch for
valve C is turned off to stop the flow of the propellent to the container.
The valve on the aerosol container is then closed and solenoid valve C-l
is opened. A 5-pound aerosol container (;) is then placed in a container
() of dry ice to cool it below the natural boiling point of the propellent,
thus acting as a vacuum pump. By this mean, all the liquid in the filling
system is remo]al and collected in the container I. Valve C-1 is left open
for approximately 5 sEconds and then closed. The aerosol container (G) may
then be discornr-ectel without danger of freezing the hand or having liquid
spurt in the eyt:. The, complete operation for filling a 5-pouid aerosol
container requires ,prpioximtely 30 seconds.
3 1/4-inch SAE 7/.i6-20 thread quick couplers.
2 solenoid valves, 3/16-inch orifice Detroit Lubricator Co.
115-230 v., a.c., No. 683-3, or equivalent.
1 double vall switch
1 laboratory balance, 10 kilogxdm3 L',picity
3 1/4-inch fle:1ble refrigeration hO1,L, 24 Inche.s long.
10 't. of Cr-pLJLr tQiibLC.
Figure 1.--Calibrated apparatus for aerosol concentrates.
UNIVERSITY OF FLORIDA
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