2-iodo-5-bromopyridine

The physical properties of the crossbow machine are quite exquisite.
Looking at its structure, it is cast in bronze, which is tough and durable. Its texture is dense, which is designed to withstand the force of the strong bow. The bronze one has a high hardness, which can ensure that the crossbow machine will not be easily damaged and deformed between repeated hair stretches, which is an important physical property.
On the crossbow machine, there are teeth, hanging knives, lookout mountains and other parts. The tooth one can hook the bow string, and its material needs to have good friction and stability. This friction force can make the tooth tighten the bow string and not slip when it is ready to go; the stability ensures that the tooth can still maintain the predetermined position under force, ensuring accurate firing. The hanging knife, that is, the trigger, also needs to be made of suitable material, and it needs to have a certain degree of toughness, so that it can operate smoothly when the finger is pulled, and it is durable. Wangshan, as the key to aiming, needs to have precise lines and angles, which depend on the precise processing performance of the production materials, so that the shooter can accurately aim at the target through Wangshan.
Furthermore, the overall design of the crossbow machine conforms to the principles of mechanics. Its size ratio has been carefully considered to achieve the best force and control effect. When the crossbow is attached to the string, the force is reasonably transmitted and distributed through the various components, so that the crossbow machine can maintain structural stability while withstanding strong tensile forces. For example, the length of the crossbow arm and the various components of the crossbow machine cooperate so that at the moment of launch, the force can be efficiently converted into the kinetic energy of the arrow, and the arrow can be launched quickly, with a long range and great power.
In addition, the crossbow machine also has unique characteristics in terms of environmental adaptability. The bronze material can resist the erosion of the natural environment to a certain extent. In humid places, although it will inevitably rust, compared with other materials, its corrosion resistance is still stronger, which can maintain its physical properties for a long time and ensure the normal use of the crossbow machine.
All these, the physical properties of the crossbow machine, its structure, material, mechanical principle and environmental adaptability, all demonstrate the excellent wisdom and exquisite skills of the ancients.

Mercury is cathode and heavy, liquid at room temperature, silver optical flow, like mercury, so it is also called mercury. Its chemical properties are unique and wonderful.
Although mercury is a metal, its melting and boiling point are very different from usual. The melting point is extremely low, about -38.87 ° C, and it is in a flowing state at room temperature, agile like a bead; the boiling point is not very high, 356.6 ° C. This property makes mercury unique in many fields such as metallurgy, and can be separated and purified by distillation.
Mercury has good electrical conductivity and can be used to manufacture various electrical components, such as mercury switches. When the circuit requires specific control, the conductivity of mercury is revealed, and with its liquid flow characteristics, the circuit can be precisely controlled to turn on and off.
Mercury has moderate chemical activity. Although it is not as active as metals such as potassium and sodium, it can also react with a variety of substances. For example, mercury can quickly combine with sulfur powder to form mercury sulfide. This reaction is quite wonderful. The two touch and combine in an instant. The yellow of sulfur and the silver white of mercury blend to form black mercury sulfide. This property is often used in the treatment of mercury leakage. By coating the sulfur powder on the mercury droplets, highly toxic mercury can be converted into relatively stable and low-toxic mercury sulfide to prevent mercury from volatilizing and poisoning.
Furthermore, mercury can form amalgam with some metals. The properties of amalgam are very different from the original metals, such as sodium amalgam, which is more stable than elemental sodium and has changed reactivity. Amalgam is widely used in dentistry and other fields. In the past, silver amalgam used for dental fillings, that is, amalgam of mercury and silver and other metals, has good filling properties and strength, and can effectively repair teeth.
Although mercury has many wonderful chemical properties, its toxicity should not be underestimated. Mercury vapor and mercury compounds are highly toxic. Inhalation or contact can seriously damage the human nervous system, kidneys and other organs, endangering life. Therefore, when using mercury, it is necessary to be extremely cautious and strictly follow safety procedures.

Among the many techniques involved in "Tiangong Kaiwu", the main use of the tube tile as a traditional building material is of great significance.
The primary use of the tube tile is roof covering. For traditional buildings, roof waterproofing is crucial. The tube tile is laid upside down and the overlying tube tile can effectively block rainwater and prevent rainwater from leaking into the house. It provides a reliable rainproof barrier for the building to protect people and things in the house from rainwater. For example, palaces, temples, dwellings and other buildings, regardless of the size, the tube tile is the key to protecting the building from wind and rain erosion.
Secondly, the tube tile has the power of decoration. Its unique shape and arrangement add a unique beauty to the building. In large palace buildings, the tube tiles are large in size, well-made, neatly arranged, showing grandeur and solemnity; in ordinary houses, although the tube tiles are relatively simple, they can also create a simple and elegant atmosphere. The tube tiles are matched with roof ridges, cornice and other building components to form exquisite architectural decoration patterns, reflecting the delicacy of ancient architectural art.
Furthermore, the tube tiles carry cultural meanings. In traditional Chinese architectural culture, building materials often contain specific cultural connotations. The use of tube tiles follows a strict hierarchy system. Different specifications and materials of tube tiles are used in different grades of buildings to symbolize the status of users. For example, the royal palace tube tiles are well-selected and made with exquisite craftsmanship, reflecting the royal dignity and majesty; while the ordinary residential tube tiles are relatively simple and simple, reflecting the differences in grades, and have become an important bearing element of traditional culture.

Mercury is a highly toxic substance, and ordinary people avoid it. However, in the records of "Tiangong Kaiwu", the synthesis method of mercury is also described.
First, the method of refining cinnabar sand. The cinnabar sand is also the natural ore of mercury sulfide. "Tiangong Kaiwu" states: "Whenever mercury is used again, it is called silver vermilion (also known as scarlet). The method is to use a new pot of iron lamps inside, and the new bottle is obliquely covered on the mouth of the lamp. The bottom of the lamp has a small storage of water to serve it. Under the kettle, the charcoal is raised to the fire. The body of silver vermilion flies lightly, and when it meets the bottom of the bottle, it will not retreat." This is to put the cinnabar in a pot, and heat it with charcoal fire. The cinnabar is heated and decomposed, and the mercury is turned into steam. When it encounters the bottom of the oblique bottle above, it condenses to obtain mercury. This process requires attention to the control of the heat. If the fire is fierce, the mercury will easily escape, and if the fire is small, the decomposition will be slow.
Second, the mud-wrapped calcination method. The book says: "If the mercury has risen to vermilion, use the chalk dust, wrap it and make a cake, and then use charcoal to calcinate it. The mercury and the chalk dust are mixed and wrapped into a cake, and then calcined with charcoal. The charcoal combustion provides heat to sublimate the mercury again. When it encounters the container above, it condenses and recovers, and the vermilion and other impurities sink below." This method also requires accurate control of the temperature and time of calcination to ensure the purity and yield of mercury.
Although mercury is toxic, the ancients did not fully understand its toxicity when operating, but they also knew that the operation needs to be cautious. For example, when refining cinnabar, the sealing of the container and the ventilation of the operating environment, although there is no comprehensive protection concept like modern science, they still try their best to avoid danger in exploration. Today, knowing the dangers of mercury, such ancient methods are only used for academic research, and have been used in actual production. Most of them use safer and more environmentally friendly modern processes to extract mercury.

When storing and transporting two ash piles and five ash piles, many matters must be paid attention to.
When storing, first, the material should be placed in a dry and ventilated place. Because the components in two ash and five ash are prone to chemical reactions in case of moisture, resulting in damage to their performance. If lime is damp, it will dissolve too quickly, which will affect the formation of pile strength. Second, different batches and types of materials must be stored separately. This is to prevent mixing and ensure the stability of material properties during construction. If confused, it is difficult to measure the final quality of the pile body.
During transportation, the first heavy packaging is tight. Both ash and ash have certain chemical activity. If the packaging is not strict, it is easy to contact with the outside air and moisture during transportation, causing deterioration. Second, the transportation tool needs to be clean and free of debris. If the transportation tool is unclean, the residual debris will be mixed into the material, or the mixing ratio will be changed, which will affect the quality of the pile body. Third, pay attention to anti-bumping during transportation. Violent bumping or layering of materials will affect its uniformity and eventually make the performance of the pile body different.
Furthermore, the transportation time also needs to be controlled. It should not be too long to avoid unnecessary changes in the material during transportation, which will affect the subsequent construction and the quality of the pile body. In short, in the storage and transportation of two-ash piles and five-ash piles, all the details are related to the quality of the final pile body, so we must not be negligent.