Formalin, an aqueous solution of formaldehyde, is colorless, transparent and corrosive in appearance. Because the formaldehyde contained is highly volatile, it will give off a strong pungent smell immediately after opening the bottle. Formaldehyde is a compound of carbon, hydrogen and oxygen. Under normal circumstances, it is a gas state and has the characteristics of strongly stimulating eye film and respiratory organs. The formaldehyde content of formalin is 35% to 40% (generally 37 formaldehyde). 10% ~ 15% methanol is also added to prevent polymerization.
The use of formaldehyde industry is particularly extensive, so the market of formaldehyde is also very large.The application involves chemistry, agriculture, fishery, medicine and so on.
In chemistry, formaldehyde liquid is a highly irritating toxic gas with flammability and corrosivity. It can detect trace amounts in general air and is very soluble in water. It is usually obtained by chemical oxidation of methanol. Formic acid solution can be obtained by methanol oxidation and formic acid can be obtained by formaldehyde oxidation.
In agriculture, formalin and formaldehyde products with a content of 40% are mainly used to control melon anthracnose, eggplant brown streak, Verticillium wilt, anthracnose, cucumber blight, Fusarium wilt, scab and vine blight. (2) Control bacterial angular spot of Cucumber (3) bacterial wilt of tomato (4) Fusarium Wilt of broad bean (5) purple spot of green onion and onion anthracnose (6) early blight, late blight, scab, bacterial wilt, stem rot, powdery scab of potato, anthracnose of kidney bean and pea and root rot of cabbage.
Applications in fish ponds include (1) pond clearing: the main component of ermalin is formaldehyde, which is a volatile substance, so it has no residual toxicity to the bottom of the pond. Considering cost saving, the formalin liquid price is lower than that of sulfur dioxide, so buy formalin is selected. (2) Immersion: formalin is the best disinfectant for mariculture, which can prevent body surface ulceration and a variety of parasitic diseases. The dosage and disinfection time are: formalin concentration 100 × 10-6～300 × 10-6, disinfection time 5 ~ 30 minutes. (3) Sprinkling: it is commonly used to treat the complications of small melon insect disease of fish and fungal and bacterial diseases of turtles. It is necessary to correctly grasp the concentration and time of use and take water change measures at any time. (4) fumigation: during fumigation and disinfection, the room temperature shall not be lower than 15 ℃ and the relative humidity shall be 60-80%, At this time, potassium permanganate can be added to the container first, and then formalin solution can be added for heating and fumigation. The purpose of disinfection can be achieved by sealing the doors and windows for more than 7 hours, and then opening the doors and windows for ventilation to eliminate the residual smell.
Notes
( l ) Formalin can only be used as soil and seed disinfection, and cannot be used by spray.
( 2 ) If precipitation occurs, it shall be used after heating and dissolving. A certain amount of alkali solution can be added to precipitate more, and fully stirred, placed for 2 days, and used after the precipitation disappears. When formalin after alkali addition is used, the dilution multiple should be appropriately reduced.