1 Bromo 3 Chloro 2 Iodobenzene

Mercury, bromine, and iodine each have unique physical properties.
Mercury, at room temperature, is a liquid metal with a shiny silver light and a heavy texture. Its fluidity is very good. If the beads are scattered, they can roll freely. The melting point of mercury is extremely low, -38.87 ° C, and the boiling point is only 356.6 ° C. And mercury is volatile to a certain extent, and it can slowly emit mercury vapor in the air. Its density is quite high, reaching 13.59 grams/cubic centimeter, so it can roll on the surface of many substances without seepage.
Bromine is the only non-metallic element that is liquid at room temperature and pressure. Its color is dark reddish-brown, and it has a strong pungent smell, which is unbearable. The melting point of bromine is -7.2 ° C, and the boiling point is 58.78 ° C. Bromine is volatile, and the reddish-brown mist produced by its volatilization is often seen in the air. Bromine is slightly soluble in water, but easily soluble in organic solvents, such as carbon tetrachloride, etc. It can show a unique color in organic solvents.
Iodine, usually a purple-black solid, with a metallic luster. Its melting point is 113.5 ° C, and its boiling point is 184.35 ° C. Iodine has a special property, that is, it is easy to sublimate. After a little heating, it will directly change from a solid state to a gaseous state, forming a beautiful purple vapor. The solubility of iodine in water is very small, but it increases in the solution of potassium iodide. And iodine will show a characteristic blue color when it encounters starch. This property is often used as a

Mercury is a liquid with a silvery white and metallic luster. It is the only metal that is liquid at room temperature. Its density is quite high, and it is more than several times heavier than water.
Bromine is a dark reddish-brown heavy liquid. It is also liquid. Under normal temperature and pressure, it evaporates reddish-brown vapor, which smells pungent. Its chemical activity is not weak, and it can react with many substances.
Iodine is usually a purple-black solid with a metallic luster. Although it is solid, it is easy to sublimate when heated, and it directly changes from solid to gaseous, showing a beautiful purple vapor. Its chemical properties are more active and can react with a variety of elements and compounds.
These three, mercury, bromine, and iodine, are all substances with distinct characteristics in the field of chemistry. The unique liquid metal properties of mercury play an important role in many industrial and scientific applications; the volatility and chemical activity of bromine make it play a key role in chemical synthesis; the sublimation properties and chemical activity of iodine are indispensable in the fields of medicine and chemical analysis. And all three have their specific positions in the periodic table of chemical elements. Their properties are not only different from each other, but also have some similarities because they belong to the same family, which are all interesting and important for chemical research and application.

1. ** Mercury (mercury is mercury) from Dan sand (mercury sulfide, HgS) **
- Dan sand (mercury sulfide, HgS) can be used as raw material to refine mercury. The ancients said: "Dan sand burns into mercury." The method is to put Dan sand in an airtight container and heat it. Dan sand is decomposed by heat, and the reaction formula is\ (HgS\ stackrel {\ Delta }{=\!=\!=} Hg + S\). Since mercury is volatile, mercury vapor is collected and condensed to obtain mercury. During this process, the heat needs to be controlled. If the heat is too strong, mercury is easily dissipated, and if the heat is insufficient, the decomposition of Dan sand is incomplete.
2. ** Refining silver vermilion with mercury (a variant of mercury sulfide) **
- Mercury and sulfur can combine to form silver vermilion. The specific operation is to take an appropriate amount of mercury, place it in an iron pot, heat it, slowly add sulfur powder, and continuously stir with a shovel. Mercury reacts with sulfur\ (Hg + S =\!=\!= Hg S\). During the reaction, the two can be seen combining, and the color changes from black to red. This red is the color of silver vermilion. It should be noted that the reaction process will produce toxic gases and should be operated in a well-ventilated place.
3. ** Use mercury to smelt lead amalgam (an alloy of mercury and lead) **
- Take lead blocks, heat them to melt, and make them liquid. Then slowly pour an appropriate amount of mercury into the molten lead liquid, and stir with a long-handled spoon. Because mercury can form alloys with various metals, mercury and lead fuse to form lead amalgam. In this process, temperature control is extremely critical. If the temperature is too high, mercury is easy to volatilize; if the temperature is too low, the fusion of the two is not good. Lead amalgam was used in some ancient processes, such as the gilt process. Lead amalgam can be applied to the surface of utensils, and the mercury evaporates when heated, leaving a gold layer, which acts as a decorative protector.
4. ** Alchemy with Mercury **
- In ancient alchemy, mercury was often an important raw material. Alchemists put mercury and other drugs, such as lead pills (\ (Pb_3O_4\)), realgar (\ (As_4S_4\)), etc. in the alchemy tripod, sealed, and heated for a long time. They believe that through the complex refining process, mercury can react with other drugs to generate medicinal pills with magical effects. However, these medicinal pills contain heavy metals, and long-term use will not only fail to prolong life, but will cause serious damage to the human body.

1 + - + mercury + - + 3 + - + arsenic + - + 2 + - + cadmium and zinc are useful in many fields.
Mercury is used in alchemy, and it was used in ancient times to seek longevity. Although it is absurd, it is also seen in one of the mysterious alchemies of ancient times. In the field of medicine, there used to be mercury-containing agents used to treat diseases, but now the toxicity of mercury is known, and its use is decreasing. In industry, mercury can be used to make instruments, such as thermometers, barometers, etc. Due to its special physical properties, it can accurately display values.
Arsenic, in ancient times, was often used as a raw material for poisons. There are many records of poisoning with arsenic in history. However, in medicine, arsenic agents have also been used to treat certain diseases. Nowadays, scientific research has shown that they have unique effects in the treatment of leukemia and other diseases. In agriculture, arsenic-containing pesticides were used to repel insects and protect seedlings, but due to the great harm to the environment and biological hazards, they are now mostly abandoned.
Both cadmium and zinc, cadmium was widely used in the electroplating industry in the past to prevent metal corrosion. However, cadmium is toxic, pollutes the environment, and endangers life. Zinc is more widely used. In the metallurgical industry, it is often fused with other metals to make alloys and enhance the properties of metals. In the human body, zinc is an important trace element, which is related to growth and development, immune function, etc. In agriculture, zinc fertilizer can promote crop growth, improve yield and quality.
These substances, either due to toxicity and need to be used with caution, or due to their unique properties, are indispensable in various fields. They should be used scientifically to weigh the advantages and disadvantages and use them rationally to ensure the well-being of humans and the environment.

"Tiangong Kaiwu" is a scientific and technological masterpiece written by Song Yingxing in the Ming Dynasty. The book records many process technologies and material storage conditions. However, the expression "1 + - + mercury + - + 3 + - + alum + - + 2 + - + sulfur" is quite peculiar, and it is not found in the conventional record method of "Tiangong Kaiwu". However, based on the description of the characteristics of various substances in the book, the following speculations can be made.
Mercury is a liquid metal at room temperature, which is volatile and toxic. Therefore, its storage should be placed in a sealed container to prevent volatilization from escaping and harming the human body and the environment. And it needs to be stored in a cool place, because the temperature will accelerate its volatilization.
Alum substances, mostly containing crystal water, are relatively stable in nature. However, moisture should be avoided to prevent changes in crystal water and affect its quality and performance. It should be placed in a dry and ventilated place to ensure that its chemical properties remain unchanged for a long time.
Both sulfur and arsenic refer to arsenic, that is, arsenic trioxide, which is extremely toxic; although sulfur is relatively weak in toxicity, it also has a certain irritating odor. Arsenic storage needs to be strictly sealed, stored in a place with special personnel and clear labels. It is strictly forbidden to mix with food and medicine to prevent accidental consumption. Sulfur should be kept away from fire sources and oxidants, because it is flammable and mixed with oxidants may cause violent reactions.
Although "Tiangong Kaiwu" does not specify the storage conditions for such a specific ratio of substances as "1 + - + mercury + - + 3 + - + alum + - + 2 + - + sulfur", according to the book's understanding of the properties of each substance, the above storage points are crucial to ensure material safety and quality.