Category Chemistry

               Mercury is the only metal that exists in a liquid state. All other metals like iron, copper or aluminium are all solids. Mercury is also called ‘quick silver’. Although it is a liquid yet it possesses all the metallic properties. It is also a conductor of heat and electricity. It freezes at –39°C and boils at 359°C. It does not stick with the walls of the glass vessels. It shines like silver. It is 13.6 times heavier than water. All these unique properties make mercury very useful for us.

               Mercury is used in thermometers. It can measure temperatures from –39° to 359° Mercury is also used in barometers which measure the pressure of the atmosphere. Normal atmospheric pressure equals 760 mm of mercury. Although mercury is poisonous, yet it is used in the manufacture of several medicines and disinfectants. About one-third of the total production of mercury each year is used for medicinal purposes.

               In nature, mercury is usually found in a combined state. Its chief ore is cinnabar. It is a red ore and is obtained from many kinds of rocks. In olden days cinnabar was used for making red pigments. When the alchemists were trying to make gold by artificial methods, they invariably used mercury in their experiments. Today mercury is used in the manufacture of several paints, caustic soda, chlorine and electrical equipments. The vermilion that Indian ladies use is nothing but a compound of mercury. 

          Diamond is the most precious and enduring substance in the world. It is the hardest material known so far. It cannot be cut by any metal or for that matter by any other thing except by another diamond only. Metal saw impregnated with diamond powder is used for cutting diamonds.

          Diamond which is a pure crystalline form of carbon is obtained from mines. At 900°C, it starts burning slowly and combines with atmospheric oxygen to form carbon dioxide. At 1000° C, it gets converted into graphite. At higher temperatures the rate of formation of graphite is faster.

          It is a good conductor of heat but a bad conductor of electricity. Its thermal conductivity is five times greater than that of copper. Diamonds vary in colour; they are either colourless or found in green, brown, white, yellow, pink and sometimes black.

          Until 1955, diamond was obtained only from mines but later certain synthetic methods for its manufacture were also developed. Diamond obtained from mines is called natural diamond, whereas the one made by synthetic methods is called artificial diamond. Africa is the biggest source of natural diamonds. About 80% of these come from this continent. Before they come to the market for sale, they are cut into different shapes and polished. The shine of diamonds remains intact even after hundreds of years.

          Synthetic diamonds were made for the first time in the world by the General Electric Co. of USA in 1955. In the synthetic process, diamonds are produced from graphite. In high temperature furnaces graphite is heated to about 3000° C under high pressure. By doing so graphite is converted into diamond. Synthetic diamond resembles the natural diamond in many respects. These are generally used in jewellery and industry. Industrial or inferior diamonds are also used for drilling and grinding. The weight of the diamond is measured in carats. One carat is equal to about 200 mg.

          Iron is found everywhere on earth. It is not only present in the minerals but also in animals and plants. It is found even in the human body. Man began to use iron about 1200 B.C. after the Bronze Age.

          Five per cent of the earth’s crust is iron. It is estimated that the earth’s core contains huge quantities of iron and nickel. It is not found in a free state but occurs in a combined state with other elements. Its chief ores are: magnetite, haematite, limonite, siderite and iron pyrites. In India, these ores are mainly found in Bihar and Orissa. To obtain the iron from these ores, they are first finely ground with coal and limestone and then heated to a high temperature in a blast furnace. The melted iron comes out from the bottom of the furnace which, on cooling, becomes solid. The iron so obtained is called ‘pig iron’ and ‘cast iron’. It contains 5% of carbon. After reducing the percentage of carbon from 2 to 0.2% it is converted into steel. The process of the manufacture of steel from cast or pig iron is called “Bessemer Process”, named after Sir Henry Bessemer, who invented it in 1850.

          Iron and steel are very useful for us. They are used in all the industries in some form or the other. Appliances of our daily use such as knives, scissors, blades, locks, buckets, utensils are all made from iron. Ships, planes, trains, buses, cars, scooters etc. are also made from this useful metal. This is also used in the construction of bridges and buildings. Various kinds of nuts, bolts, pipes etc. are also made from iron.

          Stainless steel which is a very useful metal contains 18% chromium, 8% nickel apart from steel. In India, for making stainless steel, manganese is used instead of nickel because availability of nickel is rare in our country. Stainless steel has some special characteristics – chromium stops it from rusting and it is also not affected by acids and alkalies. Other steels are made with manganese, nickel and tungsten. Iron compounds are used to make pigments, inks and film for cameras. Iron oxide is used to make the tapes for tape recorders. 

          Bread is a popular food in almost all the countries of the world. Its ingredients vary from country to country. In most of the countries, however, bread is made from wheat or rye flour. In some other places it is also made from rice, barley, potatoes, peas and beans.

          According to the recorded history, the making of bread was started around 3000 B.C. in Egypt. Yeast was also discovered there only. Nowadays the common bread is made from dough prepared by kneading flour with water. A little yeast, sugar and salt are added to it. The yeast causes the dough to rise by forming bubbles of carbon dioxide gas in the dough. The dough is then formed into the shape of a loaf and baked in a loaf tin in the oven. In the process of baking the gaseous bubbles burst resulting in small pores inside the bread. It is mainly the yeast which gives the bread its taste and flavour. You can see these pores very easily in any bread piece.

          Cakes also have pores in them, but they are produced by the baking soda and not by the yeast. Baking soda, which is the mixture of tartaric acid and sodium bicarbonate, is used in the preparation of cakes. When this mixture is added to the dough and it is baked, carbon dioxide is produced. The bubbles of this gas burst on baking causing small pores. 

          A material that burns combines quickly with oxygen in the air. Burning, then, is a rapid process of oxidation. Most materials that burn are made up of mainly carbon and hydrogen. Combustion is another name for burning.

          In 17th century combustion was explained by other theory. Antoine Lavoisier, a French Chemist, discovered in 1774, that oxygen is essential for combustion. Some substances combine with oxygen extremely slowly. In that case no light and very little heat is produced. Rusting of iron is an example of such a slow oxidation.

          For a fuel to burn, certain conditions must be met. First, a substance that can burn must be present. Second, a good supply of oxygen must be present. Third, the fuel must be treated until it reaches its ignition temperature. The ignition temperature is also called the kindling point.

          Some substances like paper have low kindling points while other fuels like coal must be heated considerably before they can burn. Some substances like white phosphorus have a very low ignition point that is why it is kept under water.

          It would be almost impossible to count the number of ways in which fire is used. Fire provides light and cooks the food. Fire is used to heat water to make steam. Steam is used to run umpteen kinds of engines. Fire is used in industries for separating metals from their ores. Fire is also used in automobiles, boats and airplanes.

          When fire is under control it might be called man’s best friend. But once it gets out of control it is undoubtedly his worst enemy. Every year fires kill thousands of lives. It can destroy buildings and forests in large a proportion if it gets out of control.