February 1948 E-74?2
United states Departmient of Agriculture
Agricultural RTesearch Administration
Bureau of Ento,. logy and Plant Q.uaaraLtine
A REVIEW OF DDT FORMITATI01iS
By R. D. Chisholm
Division of Insecticide Investigations
The outstanding effectiveness of DDT against many different insects
has resulted in the development of many methods for the formulation of
this compound to meet the requirements of specific insect problems. The
purpose of this paper is to review some of the formulation problems on
the basis of general classifications and to present examples of formulas
that have been used successfully. Some of these examples include the
mention of proprietary materials, but this implies no recommendation for
the use of any given material.
Three grades of DDT are recognized--technical, purified or aerosol
grade, and pure (Haller et al. 10). Technical DDT is a mixture containing
about 70 percent of 1-trichloro-2,2-bis(p-chlorop-enyl)ethane (commonly
referred to as p,p'-DDT), the major impurity being the o,pR.-isomer,
and has a setting point of at least 89 0. Purified or aerosol DDT is a
partially refined grade, containing more than 90 percent of p,p'-DDT,
and has a melting point of not less than 1030. Pure DDT is a highly
purified grade of p,'-DDT, melting point 108.5-109.0 (cor.), and is
used chiefly as a standard of comparison for special studies. The
chemistry of DDT has been described elsewhere (Haller and Busbey 11).
DDT formulations that have been used most generally may be classified
as water-disperuible powders, dust mixtures, solutions, emulsions, and
aerosols. The aerosols have been discussed elsewhere (Goodhue 8, 9,
Hazen and Goodhue 12, MoGovran et al. 16), but examples of formulations
of the other classes are presented in this paper. Certain characteristics
of DDT formulations have been presented by workers of this Bureau (2).
Several methods, which include micronizing, wet ball-milling, and
hammer milling, have been used to reduce DDT to particle sizes needed in
water-dispersible powders for insecticide use. The method required is
dependent upon the purity of the DDT and the proportion desired in the
finished product. In the following discussion these powders are classified
as containing (1) 90 percent or more of DDT end (2) 50 percent or less
of DDT. Some changes in procedure may be required in processing DDT from
different sources because of variations in its physical properties.
powders containing 90 percent or more of DDT. Water-dispersible
powders containing about 97 percent of DDT (Salzberg et al. 18) may be
prepared by micronizing the compound and then coating the particles to
prevent caking during storage. Highly purified aerosol-grade DDT
(melting point 106 C.) may be micronized without pretreatment. Less
pure grades acquire a high electrostatic charge during micronizing, which,
in addition to the softening caused by friction incident to grinding,
results in excessive packing in the mill. Packing can be greatly reduced
by pretreating the DDT/with an aqueous solution of an antistatic agent,
such as Aresklene 400-/ or Duponol ME, and then drying and grinding.
About 1/2 pound of agent is required for each 100 pounds of DDT. After
grinding, the DDT particles are coated by applying a film-forming agent
in aqueous solution in a heavy-duty paste mixer, drying the paste, and
grinding the cake. This coating procedure is illustrated as follows:
97.5 pounds of micronized DDT, 0.5 pound of Aresklene 400, and
2 pounds of Methocel 400 dispersed in 40 pounds of water are mixed until
a smooth paste is formed. If deflocculation and coating of the particles
are not complete, as may be determined by microscopic examination,
additional surface-active agent (about 1/2 pound of Aresklene 400)
may be required. The paste is placed in trays and dried in a Current of
air heated to 50` The dry material may be micronized or disintegrated
in a hammer mill after it has been cooled sufficiently with solid carbon
dioxide to prevent packing in the mill.
The product is free-flowing and will resist caking during storage
for several months at 65 C. It is prepared for use by mixing with water
to form a paste and then diluting the paste to the desired concentration.
Products of this nature are of value in cases where cost is not important
and a minimum of inert residue is essential.
Water-dispersible powders containing about 90 percent of DDT (Salzberg
et al. 17, 18) and sufficient surface-active agent to give a dispersed
water suspension of 1 percent of DDT have been prepared by micronizing a
mixture of DDT, an anticaking agent, a dispersing agent, and a wetting agent.
Typical formulations are as follows:
(a) (b) (c) (d)
DDT 90 90 90 90
Anticaking agent 7 6 7.5 6.5
Wetting agent 0.5 0.5
Wetting-dispersing agent 5 3 -
Auxiliary dispersing agent 1 1
Polymeric film-forming agent 2 2
l/The composition and sources of proprietary compounds are presented
in table 1.
Formulas (a) and (b) are in general useful only in soft or mooeratel-
hard water. Formulas (c) and (d) can be used in all types of water,
including sea water. If DDT of high purity (melting point 106 C. or abu,-)
is used, formulas (a) and (c) will give products of good dispersibility.
DDT of lower quality (melting point 103-106 C.) will usually disperse
more readily if formulated according to (b) or (d), which contain an
auxiliary dispersing agent.
Anticaking agents are low-bulk-density diluents, the probable function
of which is to separate the DDT particles and thus prevent packing in the
mill during grinding or coalescence during storage. One of the most
effective anticaking agents is Santocel 45-M, a silica aerogel having a bulk
density of about 7 pounds per cubic foot. This material is incompatible
with some dispersing agents that are highly effective for DDT, such as
glue, gelatin, and some types of polyvinyl alcohol. Other anticaking agents
that are more or less effective and require modifications in the formulas
presented above are 0-730, Celite 209, Sec-A-Sil, Silene, Super Absorbit,
and Superba. These modifications may require the use of a larger proportion
of auxiliary dispersing agent to prevent flocculation when the product is
diluted with water,
Some of the agents suitable for these formulas are as follows:
(1) Wetting-dispersing agents: Alkyl or alkyl aryl sulfonates, such
as Aresklene 400, Igepon T, Nacconal NRSF, Santomerse D, and Santomerse No. 3.
(2) Auxiliary dispersing agents: Polymeric aryl sulfonates, such as
Darvan No. 1 and Daxad No. 11.
(3) Polymeric film-forming agents: Elvanol 51A-05 or Methocel-400 (must
be a nonfibrous type to permit uniform blending with the DDT).
(4) Wetting agents may be any of the wetting-dispersing agents listed
above or other types that effectively reduce the surface tension of water.
The products obtained from the formulas presented are free-flowing
and are prepared for use by mixing with water to form a paste and then
diluting the paste to the desired concentration.
Wet ball-milling and dry hammer milling may be used for grinding
mixtures containing 90 percent or more of any of the grades of DDT plus
surface-active agents. The first process involves the additional step
of drying the paste and regrinding the cake. From the practical stand-
point this method may be too costly, provided the paste is not useful,
but for the preparation of' anall batches for experimentation it provides
a simple procedure. The time required for grinding is dependent upon
the type and proportion of DDT in the slurry, the concentration of surface-
active agent, and the particle size desired. In general 16 hours
(overnight) will be satisfactory for an aqueous slurry containing 30 to
50 percent of DDT and 1 percent of a polymeric dispersing agent plus
0.5 percent of a wetting agent (both based on the weight of DDT). The
several polymeric dispersing agents mentioned previously and the wetting
agents listed, to which Igepal C and Triton X-100 may be added, have been
found to be efficient.
Hammer-milling mixture .)f high DDT content (Salzberg et al. 18) 2'/
requires precooling with solid carbon dioxide to prevent packing in the
mill, and involves the hazard of moisture condensing on the cold particles
under humid conditions. Most of the particles in the products are smaller
than 20 microns, but the proportion larger than this may be too great for
best results. Experimental batches have been prepared according to the
following formula: DTfr (technical) 90 pounds, 3atocel 45M 8 pounds, and
Igepon AP Extra Concentrated 2 pounds. The ingredients are blended by
conventional method; and solid carbon dioxide (as much as 90 pounds may
be required) broken into conveniently sized pieces is distributed through
the mixture. After being chilled for about an hour, the mixture is ground
in a hammer mill equipped with a screen having circular perforations
1/8 inch in diameter. The product is brought back to room temperature and
aerated to eliminate any entrained carbon dioxide.
The foregoing formula and procedure may be modified to include 7 to
9 percent of Santocel 45-M and 1 to 3 percent of a liquid surface-active
agent such as Triton X-100, Triton X-155, Tween 85, or G7596D. For this
purpose the DDT and the surface-active agent are dissolved in a volatile
solvent, such as benzene, or the DDT is wetted with a more concentrated
solution of the surface-active agent. In either case the solvent is allowed
to evaporate and the impregnated DDT blended with the required amount of
Santocel 45-M. The mixture is processed as described above.
In general, formulations of water-dispersible powders made with
high-purity DDT (aerosol grade or better) present fewer blending and
grinding difficulties than those containing technical DDT. Such difficulties
may be largely overcome by extracting (Salzberg et al. 18) the technical
DDT with an equal weight of 95 percent denatured alcohol. The degree of
purification obtained by this method suggests that a considerable proportion
of the impurities which cause nonuniform blending or packing in grinding
are located on the surfaces of the DDT particles.
Powders containing 50 percent or less of DDT. Water-dispersible
powders containing 50 percent or less of DDT may be prepared from any grade
of DDT. The method of preparation is dependent upon the purity of the
DDT, the method of grinding, the particle size required, and the proportion
of DDT in the product. Since technical DDT is the cheapest grade, it is
generally used for such powders, but the physical properties of lots
obtained from different sources are likely to vary sufficiently to require
modification of processing methods. In general, a DDT that is not sticky
and is relatively free of hard-packed agglomerates is processed most easily.
2/ United States Bureau of Entomology and Plant Quarantine. 1945.
Final report, May 1944 to October 31, 1945, to Office of Scientific Research
and Development. Section 2, pp. 5-7. (Unpublishedc4
Mixtures containing about 50 percent of DDT may be micronized to
give products of desirable particle sizes. Hammer milling often results
in high losses due to packing in the mill unless an anticaking agent
is used and mill temperatures are carefully controlled. In both methcds
the ingredients are mixed as uniformly as possible and then ground.
Products containing 10 percent or less of DDT may be ground succesAru.
by either method. The ingredients may be intimately blended by a
preliminary coarse grinding followed by a fine grinding.
The kind of diluent to be used depends on the physical properties
of the DDT and on the DDT content and the desired storage quality of the
product. The diluent may be of low or high bulk density. The first type
is illustrated by the anticaking agents, which have been mentioned earlier
in this paper. Examples of the second type are pyrophyllite, talc,
calcite, and clays. Mixtures of both types are often used to prepare
products which have practical bulk-density values and will also resist
caking on storage at high temperatures. It is possible to use either type
alone for products containing 50 percent of DDi but diluents of low bulk
density may be impractical because of the excessive space occupied by the
product. The use of high-bulk-density diluents alone may give products
that become packed or lumpy on storage. The possible exceptions are
kaolin-type clays, which are intermediate in bulk density. For products
containing 10 percent or less of DDT the high-bulk-density diluents are
Since DDT is not wetted by water, surface-active agents are usually
added when the DDT and diluent are blended prior to grinding. Exceptions
are mixtures containing kaolin-type clays, which will be mentioned later.
A number of satisfactory surface-active agents have been mentioned in
connection with 90-percent products. These formulas may be modified to
give a mixture containing 50 percent of DDT. Since DDT is preferentially
wetted by oil, the formulation of DDT in spray mixtures which also contain
oil emulsions requires the incorporation of a protective agent, such as
glue or one of the film-forming dispersing agents, to prevent the formation
of curdy masses in the spray tank. It is best to blend the protective
agent with the DDT-diluent mixture prior to grinding. Another method
consists in wetting the ground mixture with a glue solution (1 pound of
semiliquid fish glue per gallon of water) (Fleming and Chisholm 7).
One pint of the solution is enough for 2 pounds of a 50-percent DDT
mixture. The DDT mixture and the solution, plus about an equal volume
of water, are stirred together to form a paste, which is then diluted to
the volume desired for spraying. One quart of summer-oil emulsion has
been used in 100 gallons of this spray.
Powders containing equal weights of technical DDT and a kaolin-type
clay, such as Cherokee, Homer, Sheridan 6, Topton, or Type 41, are
readily mixed with water without the aid of wetting agents. However,
protective agents are required when they are used with oil emulsions.
Cherokee clay acts to some extent as a dispersant. Products of this nature
have been stored for 3 to 4 months in open containers at 55 C. without
losing their flowability or wettability.
Dust mixtures containing 10 percent or less of technical DDT are
prepared by grindilL a blend of this material with a diluent or by
diluting a previously ground concentrated mixture. The blends may be
hammer-milled in batches without serious packing in the mill. Continuous
grinding may develop enough heat to cause troublesome packing, in which
case some means of controlling mill temperatures may be required. Dilution
of concentrated mixtures is often used, as thereby it is possible to obtain
a lower grinding cost per pound of DDT. Any of the diluents mentioned above
or others of similar nature may be-used. Some of the concentrated mixtures
may tend to pack and be distributed in agglomerates, but uniform distribution
may be accomplished by passing a preliminary mix through a hammer mill or
by brushing through screens.
In the selection of a solvent for the preparation of DDT solutions,
not only must its ability to dissolve at the temperature at which it is
used and at which it is stored be considered, but also its phytooidal
effect and its fire hazard, as well as other factors. Technical DDT is
generally used in the preparation of solutions because it is cheaper than
the other grades. It often contains insoluble material, which may require
removal by filtration to prevent clogging of small orifices or to yield
a clear solution. In exact formulations an allowance should be made for
the amount removed by filtration.
DDT solutions often contain more than one solvent. In this event it
should be recognized that the DDT capacity of a system containing both
high- and low-capacity solvents (Salzberg et al. 19) may not equal the sum
of the DDT capacities of the components. Likewise, more high-capacity
solvent is required to raise the solubility of DDT in a system containing
kerosene from 5 to 10 percent than to raise it further from 10 to 20
percent. Furthermore, the DDT capacities of solvents vary widly at normal
and subnormal temperatures. Consequently, it is suggested that each DDT-
solvent system be subjected to testing.
DDT solutions are often prepared, as concentrates for later dilution
with cheaper solvents which may be of low capacity. (Jones et al. 13,
Salzberg et al. 19). The following high-capacity solvents have been
found to dissolve between 100 and 105 grams of DDT per 100 grams of
solvent at 250-26 C.: Cyclohexanone, tetrahydrofuran, thiophene, methyl
ethyl ketone, isophorone, mesityl oxide, and dimethyl formamide. Of
these solvents only cyclohexanone and isophorone have flash points above
37.8 C., The first-named has been used most extensively. Solvents
having DDT capacities ranging from 45 to 70 grams per 100 grams of solvent
at 250-26 C. are APS-202, Aro-Sol, cyclohexene, ethylene dichloride,
Koppers 327, 1-methylnaphthalene, Velsicol AR-50, Velsicol AR-60, Solvesso
Toluol, Solvesso Xylol, Solvesso 100, and xylene. Combination systems
containing Solvesso Toluol or Solvesso 100 have DDT capacities above the
calculated amounts. Mixtures containing 80 pounds of Solvesso Toluol or
Solvesso 100 and 20 pounds of cyclohexanone have DDT capacities of 100 arid 75
grams of DDT, respectively, per 100 grams of solvent. The combination with
Solvesso 100 gives a 42-percent DDT solution with a flash point above
51.7C.. Another combination that has been used extensively, particularly
in atomized foliage sprays, consists of DDT 1 pound, xylene 1 quart, ar,
enough kerosene to make 1 gallon of solution (Shoals and Craighead 22).
Since the composition of technical DDT is variable, the solubility of a
specific lot in a given solvent may differ from published data based on
Of the low-capacity DDT solvents, petroleum fractions such as Stoddard's
solvent, kerosene, and low-gravity fuel oils have been used most extensively.
DDT is more soluble in kerosenes obtained from aromatic naphthenic-base
petroleums than in those obtained from paraffinic petroleums (Fleck and
Haller 6). In general, the solubility of DDT in kerosene increases as
the aniline point decreases. The solubility of DDT in 100 ml. of kerosene
at 270-500C. ranges from 4 grams for odorless kerosene to 16 grams tor
To DDT solutions that are to be applied on ponds and other bodies
of water it may be desirable to add a spreading agent (Salzberg et al.20).
Oleic acid, Pentamul 87, Pentamul 126, and Triton X-100 have been used
for this purpose in from 1 to 2 percent concentration.
DDT emulsions are generally prepared by diluting with water an emulsi-
fiable concentrate consisting of a solution of DDT in an organic solvent and
an emulsifying agent. High-capacity solvents are generally used in such
systems. One formulation that has been used extensively consists of DDT
25 percent, Triton X-100 10 percent, and xylene 65 percent (all by weight)
(Jones and Fluno 14. This system is readily emulsified on pouring into
water. Other emulsifying agents that are at least equally as efficient as
Triton X-100 for use with DDT-xylene or DDT-Solvesso solutions are Alkanol
WXN, Ammonyx 00, Triton X-155, and a mixture of equal amounts of Span 20 and
Tween 20 (Jones and Fluno 1, Salzberg et al. 17. U. S. Bur. Ent. and Plant
Quar. 23). One such concentrate (Salzbert et al. 2_) consists of a 90:10 mix-
ture of Solvesso Toluol and cyclohexanone 50 percent, DDT 44 percent, and
Ammonyx 00 6 percent (by weight). The proportion of emulsifying agent may
be reduced by about one-half if extremely small particle size or permanence
of the emulsion is not essential or if agitation can be maintained following
dilution with water.
Emulsions of this type which contain volatile solvents, upon
evaporation of the water and solvent, leave on the sprayed surfaces a
coating of noncrystalline DDT, which later crystallizes. Emulsions made
with less volatile solvents, such as light lubricating oils, coat the
surfaces with a solution on evaporation of the water. Such products may
be made by dissolving the DDT in a commercial emulsifiable mineral oil or
by adding a concentrated DDT solution to such commercial products.
In the formulation of DDT emulsions the use of solvents appreciably
soluble in water should be avoided, because they may cause precipitation
of DDT and clogging of spray equipment.
DDT is a relatively stable compound, and is thus compatible with most
materials that might be used with it in spraying. Chemical analyses of
the DDT deposits obtained in apple orchards sprayed with 17 formulations,
to which nicotine-bentonite or wetting agents had been added in some cases,
have shown that the DDT was substantially undecompoied (Fahey 3). After
deposits consisting of DDT and an equal weight of Bancroft clay, bordeaux
mixture, Celite, hydrated lime, limonite, pyrophyllite, or sulfur were
exposed, little or no decomposition of the total deposits could be detected
chemically (Chisholm and Koblitsky 1). It was concluded that DDT is
compatible with these materials. Some decomposition may have taken place
however, at the surface of a technical DDT deposit that became light tan
in color after exposure to brilliant sunlight for 64 hours. An indication
of decomposition has also been observed in reduced toxicity to flies of
deposits from DDT solutions after exposure to sunlight (Lindquist et al.
15). Since this reduction was most pronounced when high-boiling solvents
were used, auxiliary solvents used in conjunction with kerosene-DDT residual
sprays should be of the boiling range of kerosene or lower. The use
of strong alkalies with DDT should be avoided to prevent possible
dehydrohalogenation (Cristol and Haller 2). In alcoholic solution DDT
readily reacts with alkalies with the loss of 1 mole of hydrogen chloride
per mole of DDT and the formation of l-dlchloro-2,2-bis(p-chlorophenyl)
ethylene, which is of little or no value as an insecticide. A similar
reaction takes place at temperatures a little above the melting point of
DDT in the presence of iron and chromium oxides and chlorides which act as
catalysts (Fleck and Haller 4, 5). DDT residues from xylene emulsions
and from aqueous suspensions were less affected by light than were those
from solutions. Furthermore, certain solvents, such as nitrobenzenes and
chlorobenzenes (Fleck and Haller 5), accelerate decomposition in the presence
of these catalysts.
Table l.--Composition and sources of proprietary materials used in DDT
Name Composition Source
Diluents (High Bulk Density)
United Clay Mines
R. T. Vanderbilt Co.
United Clay Mines
Southeastern Clay Co.
Diluents (Low Bulk Density)
Dehydrating silica gel
Aluminum Co. of America
Monsanto Chemical Co.
Pittsburgh Plata Glass
Alexite Engineering Co.
Binney and Smith Co.
Aromatic petroleum fraction
Socony-Vacuium Oil C0o.
Sun Oil Co.
Standard Oil Co. of N.J.
Darvan No. 1
Daxad No. 11
Oleyl dimethylamine oxide
Sodium salt of polymerized
polyaryl sulfonic acids
Polymerized sodium salts of
E.I. du Pont de Nemours
Onyx Oil and Chemical Co.
Monsanto Chemical Co.
R. T. Vanderbilt Co.
Dewey and Almy Chemical
- 10 -
IameQ Composition Source
Sodium alkyl sulfates,
principally lauryl sulfate
Elvanol 51A-05 Polyvinyl alcohol
G-7596-D Polyethylene derivative of
Igepal C Polyether alcohol condensate
Igepon AP Extra Sodium salt of sulfonated
Concentrate ethyl oleate
Igepon T Sodium salt of sulfonated
Methocel (400 cps.)Methyl cellulose
Nacconal NRSF Sodium alkyl aryl sulfonate
Santomerse No. 3
Pentaerythritol soya bean
fatty acid monoester
Decylbenzene sodium sulfonate
E.I. du Pont de Nemours
Atlas Powder Co.
General Dyestuff Corp.
Dow Chemical Co.
National Aniline Chemical
Heyden Chemical Corp.
Monsanto Chemical Co.
Sorbitan monolaurate Atlas Powder Co.
of sorbitan monolaurate do.
Polyoxyalkylene derivati ve
of sorbitan trioleate do.
Alkyl aryl polyether alcohol Rohm and Haas Co.
Alkyl phenoxy polyethoxy-
- 11 -
(1) Chisholm, R. D., and Koblitsky, L.
1947. The effect of light on DDT residues. Agr. Chem. 2(9):35-37.
(2) Cristol, S. J., and Haller, H. L.
1945. The chemistry of DDT--A review. Chem. and Engin. News
(3) Fahey, J. E., and Rusk, H. W.
1947. Ratio of labile chlorine to total chlorine in DDT spray-
residue deposits in southern Indiana apple orchards.
Assoc. Off. Agr. Chem. Jour. 350(2):349-354.
(4) Fleck, E. E., and Haller, H. L.
1944. Catalytic removal of hydrogenchloride from some substituted
alpha-trichloroethanes. Amer. Chem. Soc. Jour. 66:2095.
(5) ---- and Haller, H. L.
1945. Compatibility of DDT with insecticides, fungicides, and
fertilizers. Indus. and Engin. Chem. 37: 403-405.
(6) ---- and Hailer, H. L.
1946. Solubility of DDT in kerosenes. Indus. and Engln. Chem.
(7) Flaming, W. E., and Chisholm, R.D.
1944. DDT as a protective spray against the Japanese beetle.
Jour. Econ. Ent. 37(1): 155.
(8) Goodhue, L. D.
1946. The evaluation of liquefied-gas aerosol formulations.
Soap and Sanit. Chem. 22(2): 13355, 155, 165.
(9) ---- and Ballinger, W. R.
1946. Accelerated aging test for insecticidal aerosols containing
DDT. Indus. and Engin. Chem., Analyt. Ed. 18:131-132.
(10) Haller, H. L., Bartlett, P.D., Drake, N.L., Newmann, M.S., Cristol, S.J.
1945. The chemical composition of technical DDT. Amer. Chem.
Soc. Jour. 67:1591-1602.
(11) --- and Busbey, Ruth L.
1947. The chemistry of DDT. U.S. Dept. Agr. Yearbook 1943-1947
(12) Hazen, A. C., and Goodhue, L. D.
1946. Insecticidal aerosols stability in storage studied by
accelerated aging tests. Soap and Sanit. Chem. 22(8): 151,
UNIVERSITY OF FLORIDA
1 2 111 111111 I I 1111111 II $1 1EIN I I
3 1262 09239 2298
(13) Jones, H. A., Fluno, H. J., and McCollougi, G. T.
1945. Solvents for DDT. Soap and Sanit. Chem. 21(11):10.
(14) --- and Fluno, H. J.
1946. DDT-xylene emulsions for use against insects affecting man.
Jour. Lcon. Ent. 39(6): 735-740.
(15) Lindquist, A. W., Jones, H. A., and Madden, A. H.
1946. DDT residual-type sprays as affected by light. Jour. Scon. I
Ent. 39(1): 55-59.
(16) "cGovran, E. R., Fales, J. H., and Goodhue, L. D.
1946. New formulations of aerosols dispersed by liquefied gases.
Jour. Econ. Ent. 39: 216-219.
(17) Salzberg, P. L., and Patterson, G. D. (E.I. du Pont de Nemours and Go.)
1945. DDT formulations. U. 8. Dept. Corn., Off. Tech. Serv., Pub.
Bd. Rpt. 27405. 26 pp. /Processed.7
(18) ---- Patterson, G. D., and Walker, I. F. (E.I. du Pont de Nemours
1945. DDT formulations--Water-dispersible powders. U. S. Dept.
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(19) --- Patterson, G. D., and Freed, W. V. (E.I. du Pont de Nanours
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U. S. Dept. Corn., Off. Tech. Serv., Pub. Bd. Rpt. 5897.
10 pp. /Processed.7
(20) ---- Patterson, G. D., Freed, W. V., and Walker, I. F. (R.I. du Pont
de Nemours and Co.)
1945. DDT formulations--Spreading agents for larvicidal oils on
water. U. S. Dept. Corn., Off. Tech. Serv., Pub. Bd. Rpt.
5944. 6 pp. /Processed.7
(21) ---- Patterson, G. D., and Freed, W. V. (E.I. du Pont de Nemours
1945. DDT formulations--Surface-active agents for emulsifiable
DDT concentrates. U. S. Dept. Corn., Off. Tech. Serv.,
Pub. Bd. Rpt. 27,402. 7 pp. /processed.7
(22) Sheals, R. A., and Craighcad, F. C.
1944. A preliminary report on aerial application of DDT for the
control of forest insects during 1944. U. S. Bur. Ent.
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(23) United States Bureau of Entomology and Plant Quarantine.
1946. DDT and other insecticides and repellents developed for tLe
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affecting animals. U. S. Bur. Ent. and Plant Quar. E-714,
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