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When Gun controlled the water, the main method he used was the method of blocking it. "Shanhaijing · Hainei Jing" says: "The flood is monstrous, and the soil of the emperor of Gun theft is flooded." The so-called blocking means trying to block the flood by means of earth embankments, cofferdams, etc.
When Gun saw that the flood was raging, he thought about the method of blocking it. When he took the soil, the soil was very magical, and it could grow on its own. Gun used it to pile up into embankments, hoping to restrain the flood and make it return to the path. However, the flood was coming, and although this simple method of blocking could resist part of the current in the short term, it was ultimately difficult to withstand the strong impact of the flood. The more water accumulates, once the embankment bursts, the harm caused will be even greater.
Gun has been controlling the water for nine years, but he failed in the end. This is because the method of blocking failed to fully consider the characteristics and laws of floods. Water is fluid, and it is difficult to solve the flood problem fundamentally by forcibly blocking it. Later, Gun's son Yu learned his lesson and changed it to be guided. He took advantage of the situation and succeeded in controlling the water. Although Gun failed to control the water, his action of controlling the water has accumulated experience for future generations, and his spirit of exploration is also worth remembering.

The mirage is formed by the strange energy in the sea, and its physical properties are particularly wonderful.
The mirage is often changeable and gratuitous, just like a tower and a city. When the world sees it, it is mostly thought of as a wonder. This is because the mirage gas is excited by hot and cold air, and the light is refracted. Although it is not physical, it appears in the void, like a dream bubble.
Its texture is formless and insubstantial, but it can be seen in its light and shadow. It is not as strong as gold and stone, nor as soft as clouds and water. It is shown in the virtual shape, as if there is nothing. When the light is suitable, the viewer looks far and wide, and sees its shape like a palace, with cascades stacked, and eaves pecked high, like a fairyland on earth.
And the air of the mirage changes with the climate. The sunny day is clear, or it is difficult to see its trace; when the clouds are hazy and the moisture is dense, it is easier to appear. Because the moisture is conducive to the twists and turns of the light, the mirage can be revealed.
And its colors are gorgeous and colorful, like the rainbow on the horizon. Red, orange, yellow and green, which complement each other, add a magnificent color to the sea and sky. The formation of this color also depends on the action of light. After refraction of light of different wavelengths, it shows different colors.
The physical properties of the mirage, with its illusory shape, insubstantial body, and changing color, exist between heaven and earth, attracting countless people's reverie. The ancients saw it, and it was mostly accompanied by myths and legends. Although people today know its scientific principles, its fantastical scenery is still breathtaking.

Mercury is a chemical substance, also known as mercury. Mercury has unique chemical properties and is worthy of further investigation.
Mercury is the only metal that exists in a liquid state at room temperature and pressure. Its metal activity is weak, and it is at the back of the metal activity order table, so it is difficult to replace with common acids. However, mercury can react with strong oxidizing acids, such as concentrated sulfuric acid and concentrated nitric acid. When it encounters concentrated nitric acid, mercury can be oxidized by it to form mercury nitrate, nitrogen dioxide and water. In this reaction, nitric acid is highly oxidizing and acidic, and mercury is used as a reducing agent.
Mercury has poor chemical stability. In air, although the reaction is slow at room temperature, if heated, it will combine with oxygen to form mercury oxide. This reaction indicates that mercury can be oxidized under certain conditions.
Mercury has significant volatility, which greatly affects its chemical properties. Due to the volatilization of mercury, mercury vapor can be formed in the air. Mercury vapor is toxic, and its chemical activity is higher than that of liquid mercury, and it is more likely to react with other substances.
In compounds, the common valence of mercury is + 1 and + 2. Mercury compounds, such as mercury chloride and mercury sulfide, also have different chemical properties. Mercury sulfide is quite stable, its color is bright, and it is often used as a pigment. Mercury chloride is highly oxidizing and corrosive. Mercury has unique chemical properties and is widely used in many fields. However, due to its toxicity, extreme caution is required when using and handling it to prevent harm to the environment and human health.

Mercury, the most spiritual thing, is quite important in the art of alchemy. The synthesis of mercury is difficult, and it involves many methods.
Ancient alchemists often use cinnabar as the starting material. The cinnabar is red and heavy in color, and its mercury content is high. Place the cinnabar in a pill furnace, control it with heat, and slowly heat it up. After high temperature calcination, the cinnabar decomposes, and the mercury escapes from it. "Baopuzi · Inner Chapter" says: "The cinnabar burns into mercury, and the accumulation changes into cinnabar." This means that cinnabar can be obtained by burning and refining mercury, and mercury and sulfur can be combined to form cinnabar.
There are also those who use bile alum as raw materials. Bile alum, blue and crystal clear, is first ground into powder and mixed with charcoal and other substances. Placed in a furnace, calcined by charcoal fire, the bile alum decomposes, and the mercury element in it gradually emerges, and mercury can be condensed.
There is also a method of lead amalgam. Lead and mercury are combined, and the two are easy to form an alloy, that is, lead amalgam. Later, by ingenious methods, mercury is separated from lead amalgam. Or by distillation, with the difference in its boiling point, the mercury is vaporized and raised, and then condensed into liquid mercury.
Alchemists must be cautious when synthesizing mercury. Because mercury is toxic, if you are not careful, you will endanger yourself. However, seeking the elixir of longevity and the synthesis of mercury are compulsory lessons for alchemists. After countless attempts and explorations, they have obtained many exquisite methods, leaving a heavy stroke on the path of alchemy.

There are many people who should pay attention to the matter of the hidden valley and the transportation of millet in the stable.
When the valley is hidden, the first valley is dry. If the grain is not dry and hidden for a long time, it is prone to mildew. You must wait for the moisture content of the grain to be moderate before entering the warehouse. And the place in the warehouse should be high and dry and ventilated to prevent moisture from invading it. You must also pay attention to the prevention of rats and insects. Rats eat and insects eat, all of which can damage the grain. You can place bait to prevent insects, and set up a machine threshold to catch mice.
As for transporting millet, the distance of the journey is related to the time consumption and the safety of the millet. If the road is long, you must worry about the bumps of the millet. The car should be stable to prevent the dumping of the millet. And when it rains on the way, cover it quickly, and do not let the millet be flooded. The transporter must also be cautious and not slack off. His work and rest should be orderly, so that the transportation of the millet is smooth.
Furthermore, both the hidden valley and the transportation of the millet are related to counting. The number of the hidden valley should be recorded in detail, so that the storage of the warehouse can be known like the back of the hand. When transporting the millet, the quantity of the transported grain must also be known, and it must not be wrong. In this way, all things in the hidden valley and the transportation of the millet can be orderly and not wrong.