An apparatus for fumigating insects with hydrocyanic acid gas in the laboratory


Material Information

An apparatus for fumigating insects with hydrocyanic acid gas in the laboratory
Physical Description:
Livingstone, E. M
United States -- Bureau of Entomology and Plant Quarantine
U.S. Department of Agriculture, Bureau of Entomology and Plant Quarantine ( Washington, D.C )
Publication Date:

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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 30352716
oclc - 781936978
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Full Text
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April 1942 ET-191

United States Department of Agriculture
Bureau of Entomology and Plant Quarantine


By E. M. Livingstone,
Division of Control Investigations l/

In studying the toxicity of hydrocyanic acid gas to the larva
of the cigarette beetle (Lasioderma serricorne (F.)) the apparatus
here described was assembled. No originality in its design is
claimed, for it embodies features contained in apparatus described
by a number of investigators who have worked with various fumigants.
The purpose of this paper is to describe the assembled apparatus,
giving suggestions for its economical construction and practical


The apparatus consists of a flowmeter, hydrocyanic acid gas
generators, fumatorium, absorption bottles, and suction apparatus.
These are connected with glass tubing in the order named in such a
way that air enters the flowmeter, where its volume may be deter-
mined, passes next through the generators where hydrocyanic acid
gas is taken up, then to the fumatorium containing the insect
material, then through the absorption bottles where the fumigant
is absorbed, and finally to the suction apparatus. Figure 1 is
a diagram showing the relationship of these units.


The flowmeter, manometer tube type, is used to measure the
quantity of air passing through the apparatus in any given period.
The flowmeter used in this apparatus is shown in figure 2. Air
passing through a horizontal glass tube, a small portion of which
is constricted, causes a differential in pressure before and after
the constriction. This differential is measured by attaching one
end of a vertical U-tube, which has previously been filled with a
fluid, in this case heptane, to the horizontal tube before the

I/ Special acknowledgment for help or suggestions is made
to W. D. Reed, in field charge, and L. H. Davis, formerly field
aide, Tobacco Insect Investigations, Bureau of'-Entomology and Plant
Quarantine, and to J. L. Horsfall, entomologist, American Cyanamid
and Chemical Corporation.


constriction and the other end after it. The pressure differential
results in a variation between the levels of the heptane in the two
arms of the U-tube, and this variation is proportional to the rate
of air flow and hence serves as a gauge of the quantity of air
that passes through the constricted tube in any given length
of time.

It is obvious, therefore, that the size of the opening in
the constricted tube and the force of suction applied to the tube
affect the rate of air flow. In addition there are other minor
factors that affect the rate of flow, or the variation in the
levels of the heptane in the U-tube, and hence it is necessary to
calibrate each meter of this type in its actual position in the
apparatus of which it is a part.

The flowmeter shown in figure 2 was made up in the laboratory
from two T-tubes; two No. 1, 1-hole, rubber stoppers; a piece of
capillary tubing about 1 inch in length (actually in this case a
piece of the stem of a broken thermometer); a section of glass
tubing of approximately the same diameter as that of the T-tubes;
and two short pieces of tubing for the purpose of making connec-
tions. Details of construction and the use of these materials
will not be set down, as it is believed that the drawing shown in
figure 2 is adequate for directions.

Generators and Trap Bottle

The hydrocyanic acid gas generators, the needle valve for
controlling the rate of air flow, and the trap bottle for collecting
any spray that may pass out of the generators with the air-gas
mixture are illustrated in figure 3. The intake end of the needle
valve is attached directly to the outlet of the flowmeter with a
rubber tube connection. The exit end is attached to the first of
the series of three generators. The needle valve should be capable
of micro-adjustment.

The generators consist of three wide-mouthed 500-cc. bot-
tles, connected in series so that a stream of air may be drawn
through them, each containing a mixture of hydrochloric acid,
sodium cyanide, and water capable of liberating the desired amount
of hydrocyanic acid gas into the air stream. A large excess of
hydrochloric acid is to be avoided. For each milligram of HCN
required per liter of air, 0.1 cc. of concentrated hydrochloric
acid and 0.057 gram of sodium cyanide (96 percent) are added to
100 cc. of distilled water. The amounts of hydrochloric acid and
sodium cyanide should be regarded as only close approximations;
the exact amount of each will vary with each lot of acid and
cyanide. The desired concentration may be readily obtained by
making up small quantities of solutions having the proportions of
acid and cyanide in different amounts for use in preliminary
analyses, and from the results of these the right amount of acid


and cyanide to use to get the wanted concentration may be calculated
or interpolated. Care should be taken to have the air-intake tubes
in each bottle extend nearly to the bottom of the solution; outlet
tubes should be well above the surface of the liquid to guard
against spray entering them. To prevent spray from entering the
fumatorium, a trap bottle, similar to those used to hold the sodium
cyanide solution but empty, is placed between the last generator
and the fumatorium.


From the trap bottle the mixture of air and HCN passes into
the fumatorium. (When the apparatus is immersed in a thermo-
regulated water bath, the gaseous mixture may be passed through
a coil of glass tubing to insure its reaching the temperature of
the bath before it enters the fumatorium.) As shown in figure 4,
the fumatorium is composed of five tubes, 1 inch in diameter and
6 inches in length, joined in series by having the exhaust of the
first lead to the intake opening of the next, and so on. The gas
enters at the top of the tubes, flows downward over the insects,
and passes out near the bottom. Each tube can be isolated from
the rest for the removal of insects by closing the proper stopcocks
located in the connecting tubes. Thus with five tubes joined in
series, as many (i. e. five) different exposures may be made without
diluting the gas mixture, for the insects may be removed from a
tube after first isolating it from the adjacent tubes. The first
lot of insects removed must be taken from the last tube in the
series, the second from the next to last, and so on. The removal
of insects from a tube interrupts the flow of the gas stream
momentarily, but as soon as the insects are removed, the tube is
closed, and the stopcocks are opened again, the flow proceeds.
Such a short interruption in flow did not seriously affect the
results of experiments under way.

Another type of fumatorium, differing from the one described
in design but not in principle, is made up of five U-shaped drying
tubes. The intakes and exits of the tubes are welded together in
a manner to permit the air-gas mixture to flow from the first to
the last. Stopcock glass stoppers are an added improvement to this
type of fumatorium, since rubber stoppers, such as those used in
the fumatorium described above, sorbb" small amounts of hydrocyanic
acid gas. The glass stoppers are used to isolate individual
tules, thus obviating the necessity of having stopcocks in the
tubes connecting the individual chambers of the fumatorium.

Absorption Bottles

The air-gas mixture, after leaving the fumatorium, passes
into one of two absorption bottles (fig. 5), each of which contains
a 5-percent solution of sodium hydroxide. The two bottles are
connected to the exit of the fumatorium with tubes having 3-way


stopcocks. The exits from the bottles are connected to the suction
apparatus by similar means. It is thus possible to direct the
stream of gas through either bottle desired. One bottle is used
for taking or absorbing samples of gas for analysis; at all times
when sampling is not in progress the flow is directed through the
other bottle. Thus all hydrocyanic acid gas is absorbed from
the stream, and only air enters the suction apparatus.

Suction Apparatus

A diagram of the suction apparatus is shown in figure 6.
The siphon bottle is -oinected directly to the exit tubes of the
absorption bottles. It should be emphasized, in setting up the
suction apparatus, that any backward flow of either air or water
in the siphon tube at any time should be prevented. Should this
happen, as when the tube is jarred or suddenly lifted from the
reservoir bottle into which the water is siphoning, air will flow
backward into the absorption bottles, causing the sodium hydroxide
solution in them to be forced over into the fumatorium. This
occurrence may be prevented by allowing the siphon tube to terminate
under water after having made a loop, the bottom of which extends
below the level of the water. For this purpose, as shown in the
diagram, the siphon tube terminates in a 1-liter distilling flask,
after having been looped lower than the exit tube of the distilling
flask. The water coming from the exit tube of the flask may be
caught readily in a measuring cylinder during sampling, or in a
large bottle at other times. In this way, the siphon tube is not
disturbed during sampling.

Calibration of Flowmeter

The flowmeter may be calibrated after the complete apparatus
is assembled, and for this purpose the cyanide solution and the
sodium hydroxide solution may be omitted from their respective
bottles and water substituted in them. The flowmeter is calibrated
by measuring the volume of air (approximately equivalent to the
quantity of water displaced in the siphon bottle) during stated
intervals, when the difference in the levels of the heptane in
the U-tube is held constant. The difference is controlled by the
needle valve between the flowmeter and the generators and may be
measured with a small millimeter rule, or, more conveniently, by
attaching a rectangular piece of stiff millimeter paper behind the
arms of the U-tube. This paper should be slightly wider than the
horizontal distance between the arms of the U-tube and as long as
the tube. It may be fastened to the back of the U-tube with
rubber bands, as such an attachment permits its being slipped
easily up or down the arms, thus ikinrg it unnecessary to adjust
the level of the liquid to the zero of the scale before an experi-
mpnt is bpgun. as would be required were the scale mounted in
a fixed position.


In the experimental work the calibrated flowmeter is used
to obtain the flow of air desired. As a further check on its con-
tinued accuracy during periods of use, occasionally in taking
samples of gas for analysis the amount of water displaced during
the sampling period is actually caught in the measuring cylinder,
as shown in figure 6, and its volume compared with the amount
indicated by the flowmeter. Should a discrepancy occur, the
flowmeter should be carefully cleaned and rechecked until the
readings are accurate. Although the volume of water displaced is
theoretically not exactly equivalent to the volume of gas passing
through the flowmeter, the difference between the two is small
and in practical work may be disregarded.

Samples of gas are taken for analysis at intervals during
the fumigation procedure, usually immediately before the removal
of a test lot of insects from the fumatorium, and at intervals not
greater than 1 hour apart. With most concentrations, the length
of a sampling period is about 15 minutes, during which time the
rate of flow should be about 30 cc. per minute. At the beginning
of a fumigation the apparatus should be flushed out, after the
insects are inserted, by increasing the rate of flow for about
1 minute.


The concentration of hydrocyanic acid gas is determined by
the Liebig method.2/ By passing a known quantity of the gas-air
mixture through a 5-percent solution of sodium hydroxide, the
gas is converted to sodium cyanide, which, immediately as it forms,
dissolves in the water of the solution. The following equation
represents this reaction:

NaOH + HCN = NaCN + H20.

To this solution a few drops of 20-percent potassium iodide
solution are added to serve as an indicator. Instead of adding the
iodide salt in solution, a few crystals of the salt dropped into the
sodium cyanide solution are equally as satisfactory for titration
purposes. The whole is then titrated with N/50 silver nitrate
solution, which by its reaction with sodium cyanide forms a complex
salt, sodium silver cyanide. The silver nitrate is added very
slowly by small drops, and after each drop the solution is gently
shaken. With the addition of each drop the solution momentarily
takes on a slight turbidity, but, until all of the sodium cyanide
has been converted, this turbidity will disappear on shaking.
When all the sodium cyanide has been converted to this salt, any
further addition of silver nitrate reacts with the potassium
indicator to form silver iodide, which, being insoluble, gives a

2/ Scott, W. W. 1925. Standard Methods of Chemical Analysis.
Ed. 4, illus. New York.


permanent, turbid precipitate, the appearance of which indicates
that the end point of the titration has been reached. The titration
is Lest when carried out in a darkened room, where, by means of
a beam of artificial light directed on the solution, the first
appearance of the permanent precipitate is easily observed. The
reactions involved in the titration are as follows:

2NaCN + AgNO3 -= NaAg(CN)2 + NaN03

KI + AgNO3 = KN03 + AgI.

From the data obtained in the analysis the concentration of
hydrocyanic acid gas may be calculated as follows:

1.08 x (Number cc. of_AgN0O3 j Mg. of HCN per liter of air.
Volume gas sample in liters

Dosages expressed in milligrams per liter may be stated in
terms of ounces per 1,000 cubic feet by use of the equation

1 mg. per liter = 1 oz. per 1,000 cu. ft.


To secure temperature control the apparatus may be immersed
in a thermo-regulated water bath.3/

Care should be taken to see that all apparatus is thoroughly
cleansed, rinsed with distilled water, and dried before use, as the
presence of water or alkali in the connecting tubes and fumatorium
will cause errors in concentration by sorbing the gas. Reduce
rubber connections to a minimum where these will be contacted by
the stream of air-gas mixture, as rubber takes up hydrocyanic
acid gas. The ends of glass tubing preferably should be ground
and pushed together as closely as possible within the rubber
connections. Rubber stoppers may be coated lightly with vaseline
to prevent sorption. In order to reduce errors that may be caused
by sorption of the gas by rubber and the glass walls, theapparatus
should be operated for about an hour previous to the start of actual
experimentation to allow their sorptive capacities to become satis-
fied to a large degree. After this period the insect material may
be placed in the fumatorium.

CAUTION: Hydrocyanic acid is a deadly poison, and this fact
should be ever kept in mind when working in the laboratory with this
-- ------------------------ ------- - --- -- -- -- -- ----
3/ Davis, L. H., and Livingstone, E. M. 1937. A Small
Thermo-Regulated Water Bath Heater. U. S. Dept. Agr., Bur. Ent.
and Plant Quar., Circular ET-98 (multigraphed).

",. -/ r BOTTLE

qI -- I -- II I- Ir F


Figure 1.-Diagram showing the arrangement of the component
parts of the fumigation apparatus.


Figure 2.--Diagram showing the type of manometer tube used as
flowmeter in the fumigation apparatus.

Figure 3.-Diagram showing needle vwlve (for controlling rate of air-
flow), hydrocyanic acid gas generators, and trap bottle.

Figure 4.--Diagram showing arrangement of 5 test tubes
connected in series to serve as a fumatorium.

figure 5.--Diagra showing gas absrtion and ampling bottls.


3 1262 092409613



Figure 6.-Diagram of arrangement of suction-creating apparatus.