2,3,5,6-tetrachloropyridine

2% 2C3% 2C5% 2C6 refers to the materials or substances commonly used in the world in the "Tiangong Kaiwu". These four things have their own special uses and are related to people's livelihood.
Both of them have a wide range of uses, or are the basic ingredients for building other things, or play a key role in certain process steps. In building construction, they can be used as adjuvants for bonding materials to make the structure more stable; in brewing, they can adjust the fermentation process, affecting the flavor and quality of the finished product. < Br >
The three, in agricultural production, are often used to fertilize the soil, nourish crops, and promote their robust growth; in handmade production, such as pottery firing, can adjust the texture and characteristics of the clay, making the finished product more aesthetic and practical.
The five, in the way of medicine, or have healing effects, and can be used in medicinal formulas to relieve people's diseases and pains; in industrial manufacturing, it can be used as a raw material for special materials, giving products unique properties and suitable for different field needs.
The six, in textile printing and dyeing, can be used as a mordant to help dyes better adhere to fabrics, making the color bright and lasting; in daily diet, or for seasoning and adding color, enriching the taste and perception of diet.
Although these four things are simple, they are all indispensable elements in the lives of all people in the world and the skills of all workers. They cooperate with each other to promote the prosperity of various causes, and have far-reaching significance for the national economy and people's livelihood. They are widely used, and they are everywhere.

The things referred to by 2% 2C3% 2C5% 2C6 are all natural numbers. Their physical properties are different.
If the husband is "2", it is the beginning of an even number. Its nature is peaceful, and it often means duality and balance. In physical images, such as yin and yang relative to each other, positive and negative phases, there is a principle of "2". For example, the molecule of water is composed of dihydrogen and one oxygen. Hydrogen and oxygen combine in a certain ratio. The number of "2" hydrogen is the property of water.
"3" is an odd number and has stability. In geometry, the triangle is the most stable shape. In the world of things, many systems are based on three, such as the three dimensions of space, length, width and height, which establish the spatial structure of all things. In chemistry, many reactions are also related to "3", such as the properties of trivalent elements, which affect the properties of compounds.
"5" is also an odd number. In the theory of the five elements, gold, wood, water, fire and earth, the basic elements of the world are summarized with "5", and each element generates and resists each other, forming a cycle of the world. In the physical world, there is also a symmetry related to "5" in the crystal structure. The senses of the human body are also "5", which can see, hear, smell, taste, and touch. These five sense the information of the outside world and interact closely with the physical world. < Br >
"6" is an even number and a composite number. In chemistry, the atomic number of carbon is 6, and its unique chemical properties can form many organic compounds and build the foundation of life. In geometry, hexagonal structures are common in nature, such as the structure of a honeycomb, which is expressed in hexagons, saving materials and having good stability.
These four, although simple numbers, have far-reaching effects in the physical world. Either the foundation of structure or the sign of elements, they are all symbols of the mysteries of nature, revealing the laws of the operation of all things.

The substance represented by 2% 2C3% 2C5% 2C6 is tetrahydrofuran. Tetrahydrofuran, a colorless and transparent liquid, has an ether-like odor, and is widely used in the chemical industry.
Its chemical properties are unique. In terms of stability, tetrahydrofuran is quite stable at room temperature and pressure. In case of open flame, hot topic or contact with oxidant, there is a risk of combustion explosion. Cover because its steam and air can form an explosive mixture, in case of open flame and high heat energy, it can cause combustion explosion.
In terms of solubility, tetrahydrofuran is the best organic solvent. It can be miscible with water, alcohol, ether, ketone, ester, hydrocarbon and many organic solvents. This property makes it often used as a solvent in coatings, inks, adhesives and other industries to help dissolve resins, pigments and other substances, so that coatings and other products are uniformly dispersed and improve performance.
From the perspective of reactivity, the presence of oxygen atoms in tetrahydrofuran makes it nucleophilic. Under appropriate conditions, it can participate in nucleophilic substitution reactions, etc. For example, under the action of bases with halogenated hydrocarbons, nucleophilic substitution can occur to generate corresponding ether compounds.
In addition, tetrahydrofuran can undergo ring-opening reactions. Under the action of a specific catalyst, the ring structure of tetrahydrofuran opens, and then participates in the polymerization reaction to form polytetrahydrofuran and other polymers. This polymer is a key raw material in the preparation of polyurethane elastomers.
In short, tetrahydrofuran is rich in chemical properties and plays an indispensable role in many fields such as organic synthesis and material preparation. However, when using it, it is also necessary to pay attention to its flammable and explosive characteristics and operate with caution.

There are several ways to make a four-strong tool.
First, use fine iron as the material. Choose the best fine iron, this iron needs to be tough in texture and has few impurities. Place it in a large furnace and calcine it with fierce fire. When the iron is burned to a red color, like the red of the scorching sun, the craftsman holds a sledgehammer and hammers hard. When a hammer falls, sparks splash everywhere, like shooting stars in the night sky. When hammering, you need to pay attention to rhythm and strength. At first, the force is slightly lighter, so that the shape of the iron gradually becomes formed, and then the force is increased to make the texture tighter. This is repeated until the texture of the iron is uniform and the shape is suitable for the needs.
Second, cast it in bronze. High-quality bronze ore is mined, and pure bronze is refined through multiple processes. Melt the bronze in a special crucible, and wait for it to turn into a hot copper liquid, which is dazzling. At this time, prepare the mold, and the mold needs to be carefully carved in the shape of Sihao, with clear texture and every detail. Slowly pour the liquid copper into the mold, and the action needs to be stable without the slightest shake. When the copper liquid cools and solidifies, carefully take out the casting, and then polish it with a fine grinding stone to make the surface as smooth as a mirror, showing the quaint luster of bronze.
Third, carve it with jade. Find warm and beautiful jade, or Hetian jade, or Lantian jade, look at its color and texture, and choose its beauty. The jade craftsman first outlines the rough outline of the four haos with coarse tools, and then uses fine knives, which are like learning, like grinding. When carving the eyes, you need to concentrate on your breath and carve out its wise and profound state; when carving the clothes, you need to make the lines smooth, as if fluttering in the wind. Every knife and every stroke, you pour your heart and effort, striving to perfectly integrate the beauty of jade with the charm of the four haos, and achieve exquisite jade.

For those with quadrotors, today's exquisite equipment is also, when using it, many matters cannot be ignored.
The first to bear the brunt is the matter of safety. When using this equipment, you must choose an open and undisturbed place, away from crowds, buildings and cables. When covering its operation, the rotor is spinning, with great force and rapid speed. If you accidentally touch people or things, you will definitely be injured. And before taking off, you need to check the aircraft carefully, depending on whether its structure is damaged, whether the rotor is agile, whether the circuit connection is stable, and whether the power is sufficient. If the power is insufficient, there is a risk of crashing during flight.
Furthermore, it is also necessary to be familiar with the method of control. The operator needs to learn its basic instructions first, such as lifting, hovering, and steering. The operation should be stable, and do not operate in a hurry, which will cause the flight to be unstable. Beginners can practice in the simulation environment first, and after mastering the skills, they can operate on the ground.
In addition, the weather conditions also have a great impact. In the event of strong wind, rain, and lightning, it should not be used. Gale can disturb its flight attitude, rain or cause moisture damage to the circuit, and lightning is at risk of damage.
And the limit of the flight area must not be followed. No-fly places, such as airports, military areas, near government offices, etc., must not be entered. This is all about public safety and order.
Although the quad rotor is exquisite and convenient, when using it, safety is the top priority, control is the key, and many factors such as weather and region need to be taken into account in order to ensure its smooth flight and safe use.