Category Science

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!

Picture Credit : Google

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 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.’