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The sea is the water of the vast desert. In the sea and river, its physical properties are unique.
The salinity of seawater is quite high, because over the years, many minerals have been carried and gathered here by rivers, and the evaporation has retained the salinity, resulting in a very high salinity. And the density of seawater is greater than that of fresh water. This characteristic makes the buoyancy of objects in seawater greater. For example, a boat sailing in the sea can move forward steadily due to buoyancy.
The temperature distribution of seawater is uneven. The surface layer is affected by solar radiation, and the temperature is relatively high. The deeper it goes, the temperature gradually drops, and to the deep sea, the water temperature is often maintained at a lower level.
As for river water, it originates from the convergence of mountains, rivers and streams, and is mostly fresh water. It contains relatively few minerals, so it has a light taste. The river water flows with a certain flow rate, and its kinetic energy can be used for hydropower generation. The temperature of river water is significantly affected by seasons and regions. The temperature in summer is often higher than in winter, and the temperature in different river basins is also different.
Due to the nature of freshwater, river water is closely related to the surrounding ecology, nourishing the vegetation on both sides of the river and providing habitat for many organisms. Although seawater is highly saline and unsuitable for direct drinking by organisms, it has given birth to a unique marine ecosystem, and many marine organisms adapt to the high-salt environment to survive and multiply. The differences in physical properties between the sea and the river create their own unique ecology and functions, which play an important role between heaven and earth.

Mercury is a chemical substance with many unique chemical properties. Mercury is liquid at room temperature and is the only liquid metal. This property makes it unique in many fields.
Mercury is relatively stable chemically and does not easily react with oxygen at room temperature. However, under heating conditions, mercury can combine with oxygen to form mercury oxide. "Tiangong Kaiwu" says: "Where mercury is used to raise the vermilion, it is called silver vermilion (i.e. mercury sulfide)." This shows that mercury can react with sulfur, and the two combine to form mercury sulfide. This reaction is often used to treat mercury leaks to reduce the toxicity and volatility of mercury.
Mercury can form amalgam with a variety of metals, and the formation of amalgam is based on the property that mercury can dissolve other metals. " There are also records about the application of amalgam in Tiangong Kaiwu. For example, in the gilt process, gold is first dissolved in mercury to make a gold amalgam, and then coated on the surface of the utensils. Heating causes the mercury to evaporate, and the gold remains on the utensils.
Mercury compounds also have various chemical properties. For example, mercury oxide is easily decomposed by heat, and mercury and oxygen are regenerated. Mercury chloride has strong oxidation and toxicity, and has specific uses in chemical experiments and industrial production. Mercury sulfide is stable in nature and bright in color, and is often used as a pigment.
The chemical properties of mercury not only give it specific value in traditional processes and modern industries, but its toxicity also needs to be treated with caution. When handling and using mercury and its compounds, strict safety regulations must be followed to prevent mercury poisoning and other hazards.

In the "Tiangong Kaiwu", mercury, commonly known as mercury, is mobile and unstable. It has a wide range of uses in the world, and it is especially important for alchemists when it comes to alchemy. Ancient alchemists wanted longevity, and they often used mercury and other substances to make alchemy, believing that taking it can prolong life and become immortal. Although there is no scientific evidence for this, mercury has a very important position in alchemy.
In the field of medicine, mercury also has its uses. In the past, doctors used mercury compounds as medicine to treat scabies, sores and other diseases. Because mercury has the ability to sterilize and disinfect, it can inhibit the growth of bacteria and help sores heal. However, mercury is toxic, and if the dosage is improper, it can cause human damage, so it is rarely used in medicine today.
Furthermore, mercury plays a significant role in the metallurgical industry. Because mercury can form amalgamates with many metals, it can be used to extract precious metals such as gold and silver. In ores, gold and silver often coexist with other things, and mercury is used to treat ores. Mercury combines with gold and silver to form amalgamates. After heating, the mercury volatilizes to obtain pure gold and silver. This is a commonly used method in ancient metallurgy, which facilitates the refining of precious metals.
Mercury also contributes to the field of lighting. In the past, mercury lamps used mercury vapor to discharge and emit light. Its luminous efficiency is quite high, the light is bright and the color rendering is good, and it is widely used in public places such as squares and streets for lighting. However, mercury is a toxic substance. If the lamps are discarded improperly, mercury leakage can easily cause environmental pollution, so it has been gradually replaced by environmentally friendly lighting lamps.
In summary, mercury has been used in alchemy, medicine, metallurgy, lighting and other fields. However, due to toxicity issues, its application has undergone many changes.

If you want to make a sea boat and a river boat, the method depends on each other. The sea boat travels in the vast sea, and the waves are rough, so it needs to be sturdy and durable, and can withstand the wind and waves.
The method of making a sea boat, the first selection of materials. It is appropriate to use tough and thick wood, such as nanmu, camphor wood, etc., which is hard and can resist seawater erosion and wind and waves. The structure of the boat body must be stable, and the keel is thick and straight, running through the head and tail, so that the spine of the boat will not fall apart due to turbulence when sailing in the sea. The boards on both sides should also be thick to resist the crashing of the waves.
Furthermore, the design of the boat type is very important. The sea boat should be pointed at the bottom, which is shaped like a blade, has less resistance when breaking the waves, and can quickly shuttle between the waves. And the stability of the pointed-bottomed boat is good, which can reduce the risk of rollover. The sail cannot be ignored, and should be designed flexibly according to the wind force and heading. With the system of multi-masted and multi-sail, the wind can be fully utilized, and the angle of the sail can be adjusted when the wind direction is different, so that the boat can travel smoothly.
As for the river boat, it travels in the river, and the water flow is relatively stable, but the river channel width is different, so it is slightly different from the sea boat method. In terms of material selection, although there is no need to pursue the extremely hard and corrosion-resistant wood like the sea boat, it must also be tough in texture and can adapt to the river environment.
The shape of the river boat is mostly flat-bottomed. The flat bottom is conducive to sailing in shallow beaches and narrow rivers, and it is not easy to be stranded. The hull of the boat is smaller and more flexible than the sea boat, so that it can be turned and passed through the curved and changeable river. The setting of the sail, according to the characteristics of the river wind, does not have to be as complicated as the sea, so that it can be powered by the wind.
To sum up, the sea boat and the river boat have different methods in terms of material selection, ship type design and sail configuration due to the different water environments they are located in. Only in this way can the boat travel freely in their respective waters.

The preservation and transportation of water is related to people's livelihood, and it is also a priority for hydraulic workers. Water, the source of life, needs to be preserved and transported with caution.
In the preservation of water, the protection of the first water source is the first priority. Mountains and rivers and springs are the source of water, and they should be kept clean and prevented from all kinds of pollution. If the source of water is filthy, the stored water must also be unclean, endangering people and animals. Furthermore, the water storage device must also be strong and dense. Ponds, ponds, and wells are all places for water storage, and their walls should be thick to prevent leakage. In the past, there were farmers who built ponds to store water, but the walls of the ponds were not solid, and the water seeped out every day, causing no irrigation of crops and no collection of particles. Therefore, the water storage device is related to the retention of water and cannot be ignored.
As for the transportation of water, the repair of the channel is essential. The road should be straight and flat, so that the water flows smoothly and does not cause congestion. And the material of the channel should be resistant to water corrosion. If rotten wood or brittle stone are used as the canal, it will collapse after a long time, and the water will overflow. In ancient hydraulic engineering, in the repair of the channel, it was often built with precision masonry and covered with plaster to make it indestructible. In addition, the observation of the terrain is also the key. Water flows to the lower part, and it can be drawn according to the terrain to save effort and be efficient. If it is done against the terrain, it will take a lot of effort, and the water will not be far away. Such as Zheng Guoqu, the hydraulic worker Zheng Guo planned ingeniously according to the topography of Guanzhong, so that the clear water flowed smoothly, irrigated the fields and made the Guanzhong fertile fields.
Furthermore, in the preservation and transportation of water, special personnel are required to perform duties, and frequent inspections are required. Watching the water dry up, the lack of inspection tools, and the blockage of the road. If there is any omission, make up for it in time. In this way, the water can be safely preserved, transported smoothly, and the well-being of the people can be sought, so that the mountains and rivers are moist and the fields and rivers are lush.