D-D mixture is apt to cause injury to plants and is therefore used almost entirely before planting. The soil should be thoroughly aerated 10 to 14 days after treatment. If that is done properly, most crops can be planted 3 to 4 weeks after treatment.

DICHLOROETHYL ETHER or 1-chloro-2- (P-chloroethoxy) ethane (C₄H₈C1₂O) is used as an insect fumigant. It is a colorless liquid at ordinary temperatures. It has a mild, distinct, but not particularly objectionable odor. Other properties: Boiling point 178 C., melting point 50 C., specific gravity 1.222 20 /4 C., vapor pressure 0.7 millimeter at 20 C., vapor weight about 4.9 times that of air.

Dichloroethyl ether is a safe fumigant as to danger from explosion. It should not be used near open flames as its decomposition products are dangerous if people breathe them. At high concentrations the vapors are irritating to the eyes, nose, and throat. If such exposure is continued for a long period, anesthesia followed by death may result. At low concentrations there is little irritation.

It is valuable as a fumigant for many soil-inhabiting insects in lawns and gardens and is useful for the treatment of soils in greenhouses. Its high boiling point and low vapor pressure allow such fumigations to proceed over a long period and provide for the retention of toxic concentrations of the vapors in the soil for extended periods. The compound will kill a number of insect species, but it may also injure growing plants. It is best used where no plants are growing. The soil should be aerated before planting. Some plants, roses and carnations among them, are more susceptible to injury than grasses are.

ORTHODICHLOROBENZENE, or 1,2-dichlorobenzene (C₆H₄Cl₂), is a colorless liquid at ordinary temperatures. It has a strong, characteristic odor. Other properties: Boiling point 180-3 C., melting point 17.5 C., specific gravity 1.3048 20 /4 C., and vapor weight about 5 times that of air.

Orthodichlorobenzene can support combustion with difficulty and burns with a sooty flame. Under many conditions it is free from fire or explosion hazards.

It is poisonous to people. Prolonged breathing of its vapors should be avoided. It may be absorbed through the skin. If spilled on the person, the wet clothing should be removed at once and the affected part should be washed thoroughly with soap and water.

It injures growing plants. Its principal use is to treat logs or trees infested with bark beetles, such as the Black Hills beetle and the Engelmann spruce beetle. Such trees are usually in a dead or dying condition. The insecticide is applied to prevent the spread of the beetles to healthy trees. During the Second World War it was used as a fly larvicide, usually diluted with fuel oil, for the treatment of pit latrines and cadavers.

PARADICHLOROBENZENE, or 1,4-dichlorobenzene (C₆H₄Cl₂), is a white crystalline compound at room temperatures. It has a characteristic odor that at low concentrations is not unpleasant. Other properties: Boiling point 173.4 C., melting point 53 C., specific gravity 1.4581 20 /4 C., vapor pressure 0.64 millimeter at 20 C., vapor weight about 5 times that of air.

Paradichlorobenzene is safe from fire and explosion hazards under most conditions of use.

It is harmful to humans. Prolonged breathing of its vapors should be avoided. At high concentrations the vapors cause smarting of the eyes and some throat irritation.

It is used in large amounts against many species, notably the peach tree borer. It is placed in a shallow trench around the tree trunk at a distance of about 2 inches and then covered with soil. As a household fumigant, particularly for clothes moths, it can be scattered on the shelves or suspended in small cloth bags from the hangers in closets. That way allows the heavy vapors to be more uniformly distributed through the closet when the door is closed better than spreading the crystals on the floor. It may be scattered on and under carpets, under furniture cushions, and in closed containers used to store blankets and other woolens. No air should circulate in the space being fumigated for at least 24 hours. Living quarters should be thoroughly aired out before they are used. Open flames should be kept away.

ETHYLENE DIBROMIDE, or 1,2-dibromoethane (CH₂BrCH₂Br), is a colorless liquid at room temperatures. It has a sharp, chloroform-like odor. Other properties : Boiling point 131.6 C., melting point 10 C., specific gravity 2.1701 25 /4 C., and vapor weight about 6.5 times that of air.

Ethylene dibromide has neither a flash point nor a fire point. There is no danger of fire or explosion. It is highly toxic to humans. Prolonged breathing of its vapors even at low concentrations should be avoided. It may be absorbed through the skin. Any clothing that it touches should be removed immediately. Parts of the body wet with it should be washed thoroughly with soap and water. Symptoms of poisoning include headache and nausea. Unconsciousness or death may occur several hours after prolonged exposure. Reddening or blistering may result from contact of the liquid with the skin.

It is, used for the control of many insects. It is effective against nematodes, Japanese beetle larvae, wire-worms, and other soil-inhabiting species. It may be diluted with a light petroleum fraction or xylene and drilled into the soil, using the same methods described earlier for D-D mixture. For other purposes, such as the control of the Japanese beetle where those methods are not practical, it is emulsified with water and applied to the surface of the soil, or infested plant balls may be dipped in a dilute water solution.

Ethylene dibromide is toxic to many plants, and soils treated with it should be aired thoroughly before planting.

It is effective against more than 50 insect species that infest grain in storage or grain mills. For that purpose it is generally mixed with other liquids, such as ethylene dichloride, carbon tetrachloride, carbon disulfide, or methylene chloride. The solutions are sprayed on top of the grain in bins, which should have tight-fitting covers. In grain mills the solutions are sprayed or poured into various parts of the machinery and splashed around the inside of empty bins.

ETHYLENE DICHLORIDE, or 1,2-dichloroethane (CH₂CICH₂CI), is a colorless liquid at ordinary temperatures. It has an odor like that of chloroform. Other properties: Boiling point 83.7 C., melting point 35.3 C., specific gravity 1.257 20 /4 C., vapor pressure 62.9 millimeters at 20 C. Its vapors are about 3.5 times as heavy as air.

Ethylene dichloride supports combustion with difficulty and burns with a. smoky flame. Under many conditions it is not dangerously explosive. Mixtures of 6 to 16 percent with air are inflammable. To eliminate such hazards, it is often mixed with 3 volumes of carbon tetrachloride.

It is toxic to humans. Prolonged breathing of its vapors should be avoided. Some of the symptoms of poisoning are dizziness, headache, or nausea. Exposure to high concentrations may produce unconsciousness and death.

It is widely used to control many insect species, usually mixed with other fumigants, as mentioned previously. It is an effective general-purpose fumigant in buildings and in vaults, where it may be evaporated from shallow pans, placed preferably in elevated locations in the enclosed space. Evaporation may be hastened by heating electrically and by blowing a stream of air over the liquid. Often it is sprayed on the surface of grain bins. Grains and seeds may be so fumigated with little danger to germination. Foodstuffs, especially those having a high fat content, may retain a disagreeable taste and odor after fumigation.

Emulsions of ethylene dichloride are used as soil fumigants. For the peach tree borer, an emulsion is poured on the ground close to (but not touching) the tree and covered with soil. Dosage and concentration are regulated according to the age of the tree. Water solutions are used against Japanese beetle larvae; infested plant balls are dipped in the solution, or it is poured on the soil of potted plants.

Ethylene dichloride is toxic to certain plants. The degree of toxicity appears to be related to plant species and to the type and moisture content of the soil.

ETHYLENE OXIDE, or 1,2-epoxy ethane ((CH₂) ,O), is a gas at ordinary room temperatures. It has a mild odor at low concentrations and a more distinct one when the concentration is increased. Other properties : Boiling point 10.7 C., melting point 111.3 C., specific gravity 0.887 7 /4 C., vapor pressure 76o millimeters at 10.7 C., and vapor weight about 1.5 times that of air.

The vapors of ethylene oxide are inflammable and at concentrations of 3 to 80 percent can form explosive mixtures with air. To reduce such hazards it is usually mixed with carbon dioxide before application or with dry ice at the time of application. A commercial mixture, containing ethylene oxide at the rate of 1 pound to 9 pounds of carbon dioxide, is available in metal cylinders.

Ethylene oxide can harm people. Prolonged breathing of its vapors should be avoided. At low concentrations its effect may be hardly detectable. High concentrations cause severe irritation of the eyes, nose, and throat, and serious injury may result from such exposure.

It is highly effective for destroying insect life in many kinds of stored products, especially packaged cereals, bagged rice, tobacco, clothing, and furs in vaults. For such purposes it is ideal because it is highly effective and leaves no odor, flavor, or deleterious residue in the fumigated product. It may, however, injure foods like nuts, dried fruits, and such fresh fruits as raspberries, blackberries, and bananas. It may lower the germination of grains and of other seeds. It does not affect the milling qualities of grains.

Another important use is to fumigate historical documents in the Federal Archives Building in Washington. It is often best employed in vacuum fumigation chambers or it may be released from cylinders or mixed with dry ice to form slush that is added to grain as the bin or elevator is being filled.

Another use is to destroy molds, fungi, and other plant life in spices.

HYDROCYANIC ACID, or hydrogen cyanide (HCN), is a colorless gas at room temperatures. For most people it has a strong, characteristic odor like that of bitter almonds, but some people cannot detect it. Other properties: Boiling point 26 C., melting point 14 C., specific gravity 0.697 18 /4 C., vapor pressure 610 millimeters at 20 C. Its vapors are slightly lighter than air.

Hydrocyanic acid is inflammable. At concentrations between 5.6 and 40 percent it forms explosive mixtures with air, but in fumigations the concentrations are so low that little danger of explosion in the presence of sparks exists. It is extremely toxic to humans and is very dangerous to use.