Remember the T-1000 terminator made of liquid metal, who fought with an ancient model of the destroyer, played perfectly by Arnold Schwarzenegger? But such a “liquid” metal actually exists, and is not just a figment of someone’s fantastic imagination. This metal is called - gallium, and it has some pretty interesting properties.
This brittle metal has a melting point of just 29.76 C, and if you hold it in warm hands for a certain time, it will begin to melt. The existence of gallium was first predicted back in 1871 by the great Russian scientist Dmitri Mendeleev, the father of the periodic table of elements. At that time, none of the “great scientific minds” could have imagined that such a metal could exist in nature, and our Russian chemist was even able to accurately predict several of its main key properties, or rather its low density and melting point. 
Gallium does not occur in nature in its pure form, but its compounds are found in negligible quantities in bauxite and zinc ores. Gallium is a soft, ductile, silver-colored metal. At low temperatures it is in a solid state, but melts at a temperature not much higher than room temperature (29.8°C). From the discovery of the element in 1875 until the advent of the semiconductor era, gallium was primarily used to create low-melting alloys. Currently, all gallium is used in microelectronics. Gallium arsenide, the main element compound used, is used in microwave circuits and infrared applications.
Nowadays, gallium is mainly used in the semiconductor industry, in the production of the most advanced digital gadgets that we use every day. By the way, gallium can be found freely available on the Internet (if you dig very hard), for those who want to conduct their own experiments. You just need to be more careful with it, although gallium metal is considered a non-toxic metal, some sources claim that prolonged exposure to this metal on unprotected skin can cause serious skin diseases: skin contact with gallium leads to the fact that ultra-small dispersed particles of the metal remain on it. Outwardly it looks like a gray spot. 
Gallium is expensive; in 2005, a ton of gallium cost on the world market $1.2 million USA, and due to the high price and at the same time great demand for this metal, it is very important to establish its complete extraction in aluminum production and processing of hard coals into liquid fuel. Due to the low melting point, gallium ingots are recommended to be transported in polyethylene bags, which are poorly wetted by liquid gallium. 
In the video you can see how small pieces of gallium begin to melt in your hand:
and how a gallium spoon dissolves in tea:
An interesting experiment can be carried out not only with the melting, but also with the solidification of gallium. Firstly, gallium is one of the few substances that expand when solidified (just like water), and secondly, the color of the molten metal is quite different from the color of the solid.
Pour a small amount of liquid gallium into a glass vial and place a small piece of solid gallium on top (a seed for crystallization, since gallium is capable of supercooling). The video clearly shows how metal crystals begin to grow (they have a bluish tint, in contrast to the silvery-white melt). After some time, the expanding gallium bursts the bubble.
The middle part of the video (the growth of gallium crystals) was sped up ten times so that the video was not very long:
Gallium is a chemical element with atomic number 31. It belongs to the group of light metals and is designated by the symbol “Ga”. Gallium does not occur in nature in its pure form, but its compounds are found in negligible quantities in bauxite and zinc ores. Gallium is a soft, ductile, silver-colored metal. At low temperatures it is in a solid state, but melts at a temperature not much higher than room temperature (29.8°C). In the video below you can see how a gallium spoon melts in a cup of hot tea.
(Total 7 photos + 1 video)
1. From the discovery of the element in 1875 until the advent of the semiconductor era, gallium was primarily used to create low-melting alloys.
2. Currently, all gallium is used in microelectronics.
3. Gallium arsenide, the main element compound used, is used in microwave circuits and infrared applications.
4. Gallium nitride is used less in the creation of semiconductor lasers and LEDs in the blue and ultraviolet range.
5. Gallium has no biological role known to science. But, since gallium compounds and iron salts behave similarly in biological systems, gallium ions often replace iron ions in medical applications.
Gallium is one of the rarest metals on our planet. It is impossible to find it in its pure form on Earth. It is found only in the form of compounds in zinc ores and bauxite. In the periodic table of Mendeleev, this element occupies an honorable thirty-first place. The metal has a unique property - its melting point is only 29.8 degrees Celsius. This is a little more than our usual room temperature. In the video you can see how a gallium spoon dissolves in a cup of hot tea in just a matter of seconds.
1. The metal was first discovered in 1875.
2. It was originally used to create low-melting alloys. With the advent of the era of semiconductors, gallium began to be increasingly used in microelectronics.
3. For the manufacture of semiconductor lasers and LEDs in the blue and ultraviolet range, gallium nitride is usually used.
4. The boiling point of gallium is much higher than that of mercury. This property allows the metal to be used in quartz thermometers (instead of mercury) to measure high temperatures.
5. A ton of gallium costs more than a million dollars and its price rises every year.
6. Prolonged contact of skin and gallium can cause acute poisoning with a fatal outcome. Its symptoms are short-term excitement, followed by retardation, impaired coordination of movements, adynamia, areflexia, changes in respiratory rhythm, complete immobility of the lower extremities. Then the person falls into a comatose state and never comes out of it.
7. Due to the fact that gallium melts very easily, it is transported only in special polyethylene bags.
Definition
Gallium (lat. Gallium), Ga, chemical element of group III of the periodic system of D. I. Mendeleev Dmitry Ivanovich, serial number 31, atomic mass 69.72; silvery-white soft metal.
Physical properties
Crystalline gallium has several polymorphic modifications, but only one (I) is thermodynamically stable, having an orthorhombic (pseudo-tetragonal) lattice with parameters a = 4.5186 Å, b = 7.6570 Å, c = 4.5256 Å. Other modifications of gallium (β, γ, δ, ε) crystallize from supercooled dispersed metal and are unstable. At elevated pressure, two more polymorphic structures of gallium II and III were observed, having, respectively, cubic and tetragonal lattices.
The density of gallium in the solid state at a temperature of T=20°C is 5.904 g/cm3, liquid gallium at T=29.8°C has a density of 6.095 g/cm3, that is, upon solidification, the volume of gallium increases. The melting point of gallium is slightly higher than room temperature and is equal to Tmelt = 29.8 °C; gallium boils at Tbp. = 2230 °C. 
One of the features of gallium is the wide temperature range of existence of the liquid state (from 30 to 2230°C), while it has a low vapor pressure at temperatures up to 1100÷1200°C. The specific heat capacity of solid gallium in the temperature range T÷24°C is 376.7 J/kg K (0.09 cal/g deg.), in the liquid state at T=29÷100°C - 410 J/kg K (0.098 cal/g deg).
Being in nature
Gallium is a typical trace element, sometimes it is also classified as rare.
Clarke (numerical estimate of the average content in the earth's crust) of gallium in the earth's crust is quite large and amounts to 1.5·10-3% (mass.). Thus, its content is higher than molybdenum, bismuth, tungsten, mercury and some other elements that are not usually classified as rare. 
The main source of gallium is bauxite (hydrated aluminum oxide). It is interesting that bauxite ores, regardless of their location and characteristics of origin, are characterized by a constantly uniform distribution of gallium in them - 0.002-0.006%. Nephelines from apatite-nepheline ores of the Khibiny Mountains contain gallium in significant quantities (0.01-0.04.
The world's main gallium reserves are associated with bauxite deposits, the reserves of which are so large that they will not be depleted for many decades. However, most of the gallium contained in bauxite remains unavailable due to a lack of production capacity, the volume of which is dictated by economic reasons. Actual reserves of gallium are difficult to estimate. According to experts from U.S. Geological Surveys global gallium resources associated with bauxite deposits amount to 1 million tons. China, the USA, Russia, Ukraine, and Kazakhstan have significant reserves of gallium.
Receipt
Gallium is a trace element that is a constant companion of aluminum and zinc, so its production is always tied to the processing of aluminum or sulfide polymetallic (especially zinc) ores. Typically, the extraction of gallium from zinc concentrates is associated with many difficulties, causing the high price of the metal, therefore, for several decades, the main source (95) of obtaining gallium has been waste from the aluminum industry, and the share of the so-called integrated waste processing (along with the extraction of zinc, indium , Germany) accounts for about 5% of production capacity.In addition, there are technologies for extracting gallium from flue dust and ash from coal combustion, as well as coking waste.
Application
Gallium does not yet have widespread industrial use.
The potential scale of by-products of gallium in aluminum production still significantly exceeds the demand for the metal.
The most promising application of gallium is in the form of chemical compounds such as GaAs, GaP, GaSb, which have semiconductor properties. They can be used in high-temperature rectifiers and transistors, solar batteries and other devices where the photoelectric effect in the blocking layer can be used, as well as in infrared radiation receivers. Gallium can be used to make optical mirrors that are highly reflective.
Gallium is expensive; in 2005, on the world market, a ton of gallium cost 1.2 million US dollars, and due to the high cost and at the same time great need for this metal, it is very important to establish its complete extraction in aluminum production and processing of hard coals. liquid fuel.
Gallium has a number of alloys that are liquid at room temperature, and one of its alloys has a melting point of 3 °C, but on the other hand, gallium (alloys to a lesser extent) is quite aggressive to most structural materials (cracking and erosion of alloys at high temperature), and As a coolant, it is ineffective and often simply unacceptable.
Gallium is an excellent lubricant. Almost very important metal adhesives have been created on the basis of gallium and nickel, gallium and scandium.
Gallium oxide is part of a number of strategically important laser materials of the garnet group - GSGG, YAG, ISGG, etc.
Gallium thermometers allow, in principle, to measure temperatures from 30 to 2230 ° C. Gallium thermometers are now produced for temperatures up to 1200 ° C.
Element No. 31 is used for the production of low-melting alloys used in signaling devices. The alloy of gallium with indium melts already at 16 ° C. This is the most fusible of all known alloys.
Which is 29.76 o C. If you place it in a warm palm, it gradually begins to change from solid to liquid form.
A brief excursion into history
What is the name of the metal that melts in your hand? As noted above, such a material is known as gallium. Its theoretical existence was predicted back in 1870 by a domestic scientist, the author of the table of chemical elements, Dmitry Mendeleev. The basis for the emergence of such an assumption was his study of the properties of numerous metals. At that time, not a single theorist could have imagined that the metal that melts in the hands exists in reality.
The possibility of synthesizing an extremely fusible material, the appearance of which Mendeleev predicted, was proven by the French scientist Emile Lecoq de Boisbaudran. In 1875, he succeeded in isolating gallium from zinc ore. During experiments with the material, the scientist obtained a metal that melts in his hands.
It is known that Emile Boisbaudran experienced significant difficulties in isolating a new element from zinc ore. During his first experiments, he managed to extract only 0.1 grams of gallium. However, even this was enough to confirm the amazing property of the material.
Where is gallium found in nature?
Gallium is one of the elements that does not occur as ore deposits. The material is very dispersed in the earth's crust. In nature, it is found in extremely rare minerals such as gallite and zengeite. During laboratory experiments, a small amount of gallium can be isolated from the ores of zinc, aluminum, germanium, and iron. Sometimes it is found in bauxite, coal deposits, and other mineral deposits.
How to obtain gallium
Currently, scientists most often synthesize the metal, which melts in the hands, from aluminum solutions that are mined during the processing of alumina. As a result of removing the bulk of aluminum and carrying out the procedure of repeated concentration of metals, an alkaline solution is obtained, which contains a small proportion of gallium. Such material is isolated from solution by electrolysis.
Areas of application
Gallium has not yet found application in industry. This is due to the widespread use of aluminum, which has similar properties in solid form. Despite this, gallium looks like a promising material because it has excellent semiconductor properties. This metal can potentially be used for the production of transistor elements, high-temperature current rectifiers, and solar panels. Gallium looks like an excellent solution for making optical mirror coatings that will have the highest reflectivity.
The main obstacle to the use of gallium on an industrial scale remains the high cost of its synthesis from ores and minerals. The price per ton of such metal on the world market is more than $1.2 million.
To date, gallium has found effective use only in the medical field. The metal in liquid form is used to slow down bone loss in people suffering from cancer. It is used to quickly stop bleeding in the presence of extremely deep wounds on the body of victims. In the latter case, blockage of blood vessels by gallium does not lead to the formation of blood clots.
As noted above, gallium is a metal that melts in the hands. Since the temperature required for the material to transform into a liquid state is slightly more than 29 o C, it is enough to hold it in your palms. After some time, the initially solid material will begin to melt literally before our eyes.
A rather fascinating experiment can be carried out with the solidification of gallium. The presented metal tends to expand during solidification. To conduct an interesting experiment, it is enough to place liquid gallium in a glass vial. Next you need to start cooling the container. After some time, you will notice how metal crystals begin to form in the bubble. They will have a bluish color, as opposed to the silvery tint that is characteristic of the material in its liquid state. If cooling is continued, the crystallizing gallium will eventually rupture the glass vial.
Finally
So we found out what kind of metal melts in the hand. Today, gallium can be found on sale for conducting your own experiments. However, the material should be handled with extreme caution. Solid gallium is a non-toxic substance. However, prolonged contact with the material in liquid form can lead to the most unforeseen health consequences, including respiratory arrest, paralysis of the limbs and a person entering a coma.