Category Chemistry

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.

Though our ancestors believed that tin plague was caused by witchcraft, we now know that it is caused by a change in the structure of the metal. After scientific studies, metallurgists found that tin- and some other metals too – has different crystalline forms at different temperatures.

At normal temperatures, the crystals that make up the metal are stable. The metal exists in the form of white tin in normal temperatures. But, when the temperature drops below 13 degrees, the crystals take a new form; the internal stresses caused by the change in temperature causes the metal to disintegrate into a grey powder. After many experiments, scientists found out that this condition can be corrected with an ‘injection’ of a substance called bismuth.

When bismuth is added to tin, it stabilizes the metal so that the tin crystals will no longer become unstable and disintegrate when exposed to severe cold. Tin can also be stabilized using antimony, another element.

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Tin plague can be really annoying and destructive. Captain Robert Scott’s was not the only expedition that was destroyed by tin plague. Tin plague had once devastated Napoleon’s plan. This phenomenon actually caused an army to lose a war.

In 1812, Napoleon invaded Russia and marched to Moscow. However, his attempt to capture the city of Moscow failed, and one of the reasons given was that his soldiers were disheartened and uncomfortable because they could not stand the cold.

Napoleon had brought a million greatcoats for his troops, but these coats all had tin buttons. You can now imagine what happened, right? In winter, the tin buttons just crumbled away leaving Napoleon’s soldiers shivering and in no mood to fight!

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We know of humans, animals and plants falling sick. But is it possible for a metal to fall sick? What is tin plague? Let us now find out the answers to these questions.

Just like you become weak when falling sick, tin grows weak in chilly weather. In very cold weather, ordinary white tin turns to a powdery grey substance that disappears after some time. This phenomenon is known as tin plague. Tragically enough, tin plague had caused the death of many members of an expedition to the South Pole that was led by Captain Robert Scott. They carried kerosene in cans soldered with tin. Kerosene was important for the expedition as it could be used to start fires in the freezing climate.

In the extreme cold weather, tin turned to a powdery dust. As a result, the cans sprung leaks and all the kerosene just dribbled away. It was a horrifying tragedy, for it meant that the members of the expedition had no kerosene to start fires to cook and warm themselves; they died of hunger and cold.

If you coat some paper with silver chloride and expose it to light, you will find out that the silver chloride will turn black where the light falls on it. If you cover it with something like a leaf, the part covered by the leaf will remain white.

If compounds of silver like silver bromide, silver chloride or silver iodide are exposed to light, they break down to form tiny particles of silver that look black. An English scientist called William Talbot used this reaction to make photographs.

To develop a photograph, a thin layer of silver bromide is deposited on a sheet of photographic paper, and exposed to light. This produces a negative image from which the photograph is printed. Digital photography succeeded this technique which is no more in use now.

Silver is one of the most romantic and sought after precious metals. In many cultures, silver is an auspicious gift. Silver’s superior properties make it a highly desirable industrial component. Silver has both industrial and decorative uses.

Since a long time, silver has been used to make exquisite jewellery and elegant tableware. The mirror in which you see your face every day is coated with silver. In ancient times, wealthy people had mirrors and many other everyday objects made of pure silver.

Silver is a very good conductor of electricity, so it is widely used in industry, especially in electronics where it is used for printed circuit boards and electrical contacts. It is also used as a catalyst and is important in the production of solar energy. Another fascinating aspect of silver is the use of silver iodide in fighting tropical storms.

Silver played an important role in the history of Argentina, a South American country at the bottom of the continent. The name Argentina comes from the Latin ‘argentum’, meaning silver. ‘Argentina’ therefore means the ‘land of silver’. But how did this country get its name? Let us take a look.

In the early 1500s, Spanish conquistadors had heard tales about a land ruled by a White King that was rich in silver. They set on a voyage up a river in search of this wealthy kingdom. They discovered a group of native Indians, who presented them with so many silver objects that the river was named ‘Rio de la Plata’ or Silver River. In time, the country itself was called La Plata which means ‘silver’ in Spanish. When the rule of Spain ended, the name was changed to Argentina, from the Latin word ‘argentum.’

In olden days, silver was used to make coins in many kingdoms. The practice of using silver coins slowly gained popularity. But silver was a rare metal. Later it was found out that the cost of silver used for making these coins was a lot higher than the value of these coins. But, there was a solution to this problem-add another element to silver!

            Finally, after a lot of experiments, it was found out that copper could be mixed with silver to make coins that looked like silver, which was much cheaper than the older practice. Since then, copper-silver alloy is used to make silver coins.

Today, if a silver coin is actually made of pure silver, the metal would cost more than 20 times the value of the coin. However coins of pure silver are still available. People buy them as an investment.