Category Chemistry

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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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.

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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Iron was popular in ancient India. The extraction of iron in India dates back to the 4th century BC. Iron was used to make ornaments, weapons and buildings.

Indian smiths had developed many advanced techniques of processing iron that did not exist anywhere else in the world in those days. Expert craftsmen created many beautiful structures from iron which have lasted centuries without rusting.

In Delhi, there is a famous iron pillar that stands testimony to the high level of skill achieved by ancient Indian ironsmiths. In fact, it has withstood corrosion for the last 1,600 years! This pillar had sparked the interest of many material scientists across the world.

The iron beams in the Surya temple at Konarak in coastal Orissa, and the iron pillar at Mookambika temple are also examples of the skill of the ancient ironsmiths in treating iron so that it became rust- resistant.

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Gold secured a place in the hearts of early humans the moment the sparkling yellow grains were discovered for the first time. Humans have longed for gold ever since then. Men fought for it, women adored it.

We know the story of king Midas. According to Greek mythology, king Midas was granted the boon to turn anything that he touches into gold. He jumped with joy when the leaves and fruits that he touched turned into gold. However, he soon realized that the boon that he had asked for was in fact, a terrible curse.

He could not eat or drink, nor even wash his hands. Everything he touched turned into gold the moment he touched it. The boon was finally taken back after begging the gods for mercy.

The story of king Midas conveys the importance that was associated with gold. He asks nothing else but gold. Ancient kings and queens have always tried to amass as much gold as they could. This is why gold has been called the ‘king of metals’ and ‘the metal of kings’.

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