My Science School

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.

We have heard many stories of people drinking from silver cups and eating from a silver platter. While we use a glass or steel tumbler to drink water, many of our ancestors used tumblers made of silver. More than a practice that showed off wealth, this had something to do with hygiene. Silver has excellent anti-bacterial properties. It kills harmful bacteria in water. In fact, a few millionths of one gram, is enough to purify a litre of water! Our smart forefathers knew this, and that is why they used to store water in silver vessels, and drink from silver cups.

Even today, some people drop a few silver coins in their drinking water to purify it. Though we are sure about the anti-bacterial properties of silver, it is always safer to boil water before drinking it as there are so many germs today.

 

In our society, gold is seen as a symbol of wealth. Most of the gold that we see around us is in the form of jewellery and other artefacts. But gold has more desirable qualities than its beauty which makes it a valuable metal in the industry.

The properties of gold make it vital for the manufacture of components used in a wide range of electronic products including computers, telephones, cellular phones, and home appliances. Gold is used for shielding satellites and spacecraft from solar radiation because it is an excellent reflector of heat.

Gold is a vital element in medical research; it is even used in the direct treatment of arthritis and some other diseases. Gold is also widely used in dentistry; though getting a gold tooth to replace a natural one is rather expensive!

In some Asian countries, gold is used in food and drink, from fruit jelly to coffee. Some sweets are covered with gold leaf.

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You might have seen jewellery advertisements talking about something called carats. But what are carats? A carat is the proportion of gold in an alloy. But why do we mix gold with other elements? Let us take a look.

Pure gold is very soft. It is not possible to make jewellery and other artefacts with pure gold as it is not hard enough. Gold in its pure form breaks easily. So, it is often mixed with copper, silver or other metals to make it easier to work with. Pure gold is always 24 carat. But, most of the jewellery that we wear is made of 22 carat gold. If there is a higher proportion of copper or silver, the gold may be 18, 14, or even 9 carat gold.

The cheapest jewellery will be made of 9 carat gold, and the most expensive, of 22 carat gold. The greater the amount of gold in the mixture, the more expensive it will be.

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Archimedes is famous for the Archimedes Principle, which states that when an object is immersed in a fluid, it will displace a volume of fluid equal to the volume of the portion of the object immersed. There is an interesting tale behind this principle.

Archimedes used this principle to prove that a jeweller was cheating the king. The king suspected that a solid gold crown he ordered was partly made of silver. To find out if it was true, Archimedes took two pieces of pure gold and pure silver of the weight of the crown. He then immersed the gold, the silver, and the crown - one after the other - in a container filled to the brim with water. He then measured the volume of water that overflowed with each material.

Archimedes found that the crown displaced more water than the gold, but less than the silver. This proved that the crown contained some metal other than gold or silver, and that the jeweller had stolen some of the gold given to him, and replaced it with a cheaper metal!

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Around 1500 tons of gold are produced around the world every year. Most of this gold comes from South Africa. Two methods are used to extract gold from the rocks where it is found. Gold can be extracted using mercury. The minerals containing gold are mixed with mercury. The gold will dissolve in the mercury to form an amalgam or alloy of mercury. The amalgam is then filtered and heated so that the mercury evaporates, leaving pure gold behind. In another popular method, the minerals containing gold are added to a sodium cyanide solution.

This solution reacts with the gold to form a new compound. The solution is then filtered to remove impurities. Later, zinc is added to the solution which reacts with the compound to produce pure gold.

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Gold played an important role in the life and culture of ancient Egypt. Ancient Egyptians considered gold divine and indestructible. It was associated with the brilliance of the sun and the sun god Ra was called ‘the mountain of gold’. Gold was widely used in ancient Egypt to make ornaments and other objects of value.

The pharaohs of ancient Egypt used gold lavishly in their tombs, on the floor, on the walls, and in the huge sarcophaguses or burial urns. It was their belief in the magic and spiritual power of gold that led the Egyptians to bury their dead adorned with golden amulets and jewels, making their tombs great treasure troves of gold.

No wonder, ancient Egypt was regarded as one of the richest countries in the world. In fact, Egypt was known as ‘the golden land’.

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The practice of alchemy flourished in ancient civilizations and later, it gained popularity in Europe in the 19th century. The alchemists, people who practiced alchemy, searched for means to transform ordinary metals like lead into gold.

Alchemy flourished in the Middle Ages. This was due to the increasing popularity of gold. Kings, queens and common people desired gold alike. Furnaces were lit in gloomy basements of stone castles and secret experiments were performed with some mysterious liquids. Many alchemists believed that the purity of mind, body and soul was essential to pursue alchemy. They also believed that alchemy could prolong life.

In the Middle Ages, it was believed that a substance called the ‘philosopher’s stone’ could turn other metals into gold. Needless to say, no one ever discovered such a stone, nor did the experiments of the alchemists meet with any success.

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We all are familiar with the stories where kings reward artisans, craftsmen and good subjects with gold coins.

Gold was used as currency in many kingdoms. But where was it used as currency for the first time? Lydia, an ancient kingdom in western Turkey is believed to be the pioneer of gold currency. Lydia was a fertile kingdom, but its greatest asset was the river Pactolus; it carried gold deposits.

Around 643 to 630 BC, the Lydians began producing the first coins. They were quite crude, and were made of electrum, a naturally occurring pale yellow mixture of gold and silver. By about 560 BC, the Lydians had learned to separate the gold from the silver following which, King Croesus issued the world’s first gold coins. Shortly afterwards, in 546 BC, King Croesus was captured by the Persians, who came to adopt gold as the main metal for their coins.

Soon, gold coins were being used in many other ancient countries. But the credit of introducing gold currency lies with the Lydians.