My Science School

Let us now look at the varied uses of mercury. Mercury is used as an electrode in the production of chlorine and sodium hydroxide. It is also used in certain electric batteries.

It is used in barometers and manometers. It is also used extensively in thermometers. Mercury is important as a liquid contact material for electric switches. It was also used in mercury-vapour lamps that were used for street lighting.

Mercury forms a special type of alloy with some metals like silver, and tin. These alloys are used in dentistry for filling teeth. Several compounds of mercury are used as disinfectants.

They are also used to make substances including insecticides and rat poison. Mercuric oxide is used in skin ointments, though of course people handle it with a great deal of care now, because of the danger of mercury poisoning.

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Mercury is not a common metal. It is rarely found on Earth’s crust. In fact, it forms only 0.00005 per cent of the crust. However, there are more than 20 minerals that contain mercury. It is found in cinnabar, cordierite, livingstonite and some other minerals, with cinnabar being the most common ore.

Mercury ores usually occur at hot springs or other volcanic regions. Globally, mercury is most commonly produced in Spain; the Almaden mine there is known for its high quality mercury. It is also obtained from the United States and Italy.

Mercury is named after the planet Mercury, which in turn, is named after the Roman God Mercurius, the God of trade, profit and commerce. Mercury is sometimes called quicksilver because of its silver colour. In fact, its chemical symbol ‘Hg’ comes from the Greek word ‘hydrargyrum’ which means ‘water silver’.

You might already know that alchemy flourished in the Middle Ages when people began going crazy over gold. They also believed that mercury could be converted into gold if they found the philosopher’s stone.

Alchemists would heat mercury with nitric acid to prepare mercuric oxide. The reaction produced a thick red vapour, which hovered over the surface of the solution. The mercuric oxide that was formed would fall to the bottom of the liquid in the form of bright red crystals.

Many of the alchemists used these crystals to fool people about the supposed powers of mercury including the power to grant eternal life. Some alchemists also used mercury to demonstrate that gold could be made artificially.

There are evidences that suggest that mercury was known to humans before at least a thousand years. Mercury has been found in Egyptian tombs that date back to 1500 BC. The ancient Chinese and Indians were familiar with the liquid metal. In fact, our ancestors thought of mercury as the first matter from which all metals were formed.

In countries like India, China and Tibet, it was believed that mercury could prolong life, heal fractures, and maintain good health. While the ancient Greeks used mercury in ointments, the Romans used it to make cosmetics.

Our ancestors believed that varying the quality and quantity of sulphur contained within the mercury could produce different metals. They even tried to transform mercury into gold. Needles to say, they were not successful!

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As already mentioned, mercury was widely used to make ointments, cosmetics and even dental fillings. But studies have revealed that the compounds and vapours of mercury are potentially hazardous as it can cause poisoning.

In fact, mercury poisoning is something to be feared as it does not affect just one part, but each and every system of the human body. It can cause other diseases as well.

Health problems caused by mercury depend on how much of it has entered your body, how it entered your body, how long you have been exposed to it, and how your body responds to mercury. There are many possible ways to get poisoned by mercury.

Some cosmetics can be harmful to us as it contains compounds of mercury. The people working in the paint industry are at risk as paint uses some compounds of mercury. Eating fish that have been exposed to mercury in the environment is also very dangerous.

In 1956, thousands of fishermen and their families in the southern Japanese city of Minamata fell ill because they ate fish that had been contaminated with mercury.

We have discussed the harmful effects of lead at length now. But why was lead widely used despite its hazardous impact? Undoubtedly, it was because lead was a useful metal. Let us now look at some of the usages of lead.

In the olden days, lead was used as a building material. It was used as a pigment for glazing ceramics. Water pipes were coated with lead. Today, the most prominent use of lead is to build lead-acid storage batteries. The electrical systems of vehicles, ships, and aircraft depend on such batteries for startup, and in some cases, batteries provide the actual motive power.

Have you heard of sound-proof rooms? Lead is used for soundproofing office buildings, schools, and hotels. It is widely used in hospitals for protection against X-ray and gamma radiation. Lead is also employed as a shield against harmful nuclear radiation.

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Earlier, lead was mixed in petrol for better performance. Lead was useful in helping the car engines better. If the petrol in the car burns too quickly, the engine starts rattling. Adding lead to petrol minimized wear and tear. But it created more problems than the benefits it offered.

Lead was poisonous and burning leaded petrol was a suicidal idea. It also increased pollution considerably. Studies conducted in different parts of the world proved that unleaded petrol caused much lesser pollution than leaded petrol. So, many countries have banned the use of petrol with lead added to it, and now only unleaded petrol is used.

Different additives have now replaced the lead compounds. The most popular additives include aromatic hydrocarbons, ethers and alcohol. However, fuel containing leads continue to be sold for off-road uses, including aircraft, racing cars, farm equipment, and marine engines in some parts of the world.

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The usage of lead has a history of more than a thousand years. Humans have mastered the technique of extracting lead from its ores for more than a thousand years. Lead is hardly found as a free metal in nature.

The main ore of lead is lead sulphide, which is also known as Galena. Galena is crushed to a fine powder, and then mixed with water and some other chemicals. As a result of this, the lead sulphide will float to the top in the form of froth, and the waste rock will sink to the bottom. The froth is then dried and mixed with limestone to remove the sulphur from the lead sulphide. This leaves behind lead oxide.

The lead oxide is further crushed and heated in order to obtain molten lead after removing the oxygen molecules. It is purified further to make it ready for sale.

There is no doubt about the importance of lead in the lives of ancient humans. It was used to make pipes, vessels and a lot of other things. However, lead was also looked at with fear; this metal was vital in many torture mechanisms that were used to punish criminals.

In the Middle Ages, lead was used as an instrument of torture. Hot molten lead was poured into the ears of anyone suspected to be against the religious beliefs of the time. This was because lead melts easily. In Venice, prisoners were held in an attic with a lead roof that would make the cells unbearably hot in summer and unbearably cold in winter. Their screams of agony could be heard all day even outside the prison!

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To find one gram of silver, you need to drill through at least 20 tons of rock! Silver makes up only a tiny proportion of the Earth’s crust. Silver indeed is a rare metal.

Silver is found either as a free metal, or in combination with other elements. We can extract silver from silver ores; the most prominent silver ore is asanthite or argentite. Lead sulphate or Galena is another important source of silver. The principal sources of silver are the ores of copper, copper-nickel, lead, and lead-zinc obtained from Peru, Mexico, China, Australia, Chile, Poland and Kosovo. Peru and Mexico have been mining silver since 1546 and are still major world producers of this lustrous metal.

About 18,000 tons of silver are produced every year. But extracting silver is a tough process. A lot of it comes from the waste left behind after refining copper, lead or zinc. Although silver is relatively scarce, it is the most plentiful and least expensive of the precious metals.

The ancient Roman Empire is known for its magnificent wealth and rich culture. Despite all their glory, many Romans died young. After scientific enquiries, it was concluded that many Romans died young because of poisoning. This happened because they used one metal without knowing about its hazardous effects.

Lead was one of the most popular elements in ancient Rome. They used plates and vessels made of lead. Even water pipes were made of lead. The water in the pipes reacted with lead to form lead carbonate, capable of causing many chronic diseases. Many people died of various ailments and the Empire steadily declined, all without the Romans having any idea of what went wrong.

Of course, there were other reasons too for the decline of the Roman Empire, but it is still believed that lead played an important role in its downfall and collapse.

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Lead is of great use in the production of many products. For decades, it was added to paint to make it last longer and flow easier. Lead was included in fuel to make engines run better. We even used to manufacture water pipes made of lead.

Solder was also made with a lot of lead in it because it melted at a low temperature, and was much easier to use. These are but a few uses of lead. Yet, the use of lead is not encouraged much nowadays. Want to know why?

Though lead is useful, it is a poisonous metal. Even tiny amounts of lead can harm you. Inhaling lead can cause severe stomach ache and consumption of even the tiniest amount of this deadly metal is enough to paralyze you. Young children who breathe or swallow lead suffer brain damage, and become deaf and blind. Therefore, today, we have strict rules for controlling the use of lead.

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Let us now look at the various uses of tin. Tin is used to coat other metals to prevent corrosion. It is an alloying agent. Some of the important tin alloys include soft solder, type metal, fusible metal, pewter, bronze, bell metal, Babbitt metal, white metal, die casting alloy, and phosphor bronze.

Tin is used for making window glasses. The glasses used for making the windows of your classroom and houses are made by using a process which involves floating molten glass on molten tin to produce a flat pane surface. Tin salts are sprayed onto glass to produce electrically conductive coatings. These salt treated panes can be used for panel lighting and for frost-free wind-shields.

Tin is also used to make agricultural goods like fungicides. Some compounds of tin are very useful in the manufacture of paints. Tin is also used to make superconductive magnets that generate enormous field strengths, but use practically no power.

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All of us use tins at our homes. Tins are air-tight containers made of thin metal. If you go to the supermarkets, you would find shelves in the food section loaded with cans of preserved food. What are these tins made of? Tin cans are not made solely of tin, but rather tin-coated steel or tinplate. The properties of tin make it ideal for making cans. Therefore tin is known as canning material.

Tin does not react with oxygen, water, or the acids in food and its salts are completely harmless to humans. This is why millions of tons of meat, fish, fruits and vegetables are preserved in tin cans.

The mining of tin is believed to have begun around Classical times, in Cornwall and Devon. Within the civilizations of the Mediterranean, a thriving tin trade developed, and to this day, tin plays a very important role in our lives, directly and indirectly.

Tin is rarely found in its free form in nature. To obtain tin, tin ores have to be smelted first. Tin oxide or cassiterite is one of the main ores of tin. Let us now take a look at how tin is smelted. The crushed cassiterite is heated and stirred with coke for about 15 hours. The coke provides enough carbon needed for removing oxygen from tin oxide.

The impurities that float to the top are then removed. The molten tin is poured into moulds and is left to cool down. The solidified tin is then refined to remove any impurities that may still be remaining.

Refining tin is another process altogether. To refine tin, it is heated to about 1200 degree Celsius in vacuum. When the tin melts, remaining impurities will boil away to leave behind tin that is 99.85 per cent pure. By using a process called electrolysis, tin can be refined further.