My Science School

           Ordinary water does not remove dirt from things because grease and water do not mix. So soap is one of the most common cleansing agents used all over the world. People use soaps and detergents to clean their skin, clothes, utensils and many other objects. How does soap remove dirt?

          Soap is basically a fatty acid salt which can be obtained by boiling fats or oils together with an alkali. When oil is allowed to react with caustic soda solution, the chemical reaction produces soap and glycerin. Both are separated. When soap is applied on a cloth, its molecules break into fatty acid ions and sodium ions. Fatty acid ions are repelled by water but are attracted towards greasy dirt particles. They surround each grease molecule and remove it from the surface of the cloth. These are carried away by the water and consequently the cloth gets cleaned. Other actions, such as agitating, squeezing or rubbing and rinsing help loosen dirt and grease so that water may carry them away.

          Today, chemical cleaners called detergents are more and more in use instead of ordinary soaps. Detergents clean better than soaps in hard water, (the ‘hardness’ of the water is caused by the presence of calcium and magnesium salts. Soap does not make much lather in hard water) but they do not, by themselves, make suds. Suds are not necessary for cleaning but substances that make suds are added to detergents.

          Many substances are added to a crude soap to make it suitable for use as toilet soap. Coconut oil is added to make it lather quickly. Dyes, perfumes, water softeners and germicides, which are tiny substances that kill germs, are also added. 

          Man has been using artificial lights ever since he discovered fire. In the beginning, it used to be just the log fire, and then the wick on the edge of a stone bowl filled with animal’s fats and then the candles. A great step in this field was made by Thomas Alva Edison who invented the modern electric bulb in 1878. And by 1930, the scientists of America and Europe had developed the wonderful fluorescent tube.

          A fluorescent tube light consists of a long glass tube coated with a fluorescent material. Two tungsten electrodes are fitted at the end of this tube. The tube is evacuated and filled with a little amount of mercury and argon gas. When the tube is connected with the electric line, tungsten electrodes get heated up and start producing electrons. These electrons collide with mercury atoms and produce ultraviolet and visible light. Ultraviolet light, on colliding with fluorescent material, is turned into visible light. The colour of this light depends upon the fluorescent material.

         These tubes are coated with calcium tungstate to produce blue light. A coating of calcium silicate produces pink colour while that of zinc silicate produces green light.

         A fluorescent light is definitely an improvement on the ordinary bulb. Its electric consumption is very low but the light-producing efficiency is better than the bulb.

 

          Cement, today, is by far the most useful of all the building materials. It is being used in all countries throughout the world as a binding material in the construction of buildings and civil engineering. It is a grey coloured powder. When mixed with water and allowed to settle for some time, it becomes as hard as stone. The principal minerals in cement are lime (which comes mainly from limestone), silica and alumina (which are provided by clay). Cement was discovered by the Romans around 250 B.C. They made it by mixing slaked lime and sand with volcanic ash. As it was obtained from a place named Pozzuoli, it was called pozzolana. Upto the middle of the 18th century, it was in common use. In 1757 an improved version was developed by John Smeaton, a British engineer. It was obtained by heating a mixture of slaked lime and clay. It remained in use for many years.      

          The most common kind of cement was made by an Englishman, Joseph Aspdin in 1824. When set, its colour would become similar to that of Portland stones. Hence, it was called Portland cement. Portland cement is made by mixing one part of clay and three parts of limestone in a very hot oven. Both the raw materials are powdered with the help of a crushing machine and mixed together by a blending mill. This mixture is then sent to the hot oven called a kiln. It is heated to about 1500-1600° C to form a hard mass called clinker. When the clinker cools down, it is grounded into a fine powder with mineral called gypsum in a grinder. About 3% of gypsum is added to it to regulate the time that the cement takes to harden. This is known as the Portland cement.

          In India, the Indian Cement Company was established at Porbunder in 1914. Today, cement is being manufactured on a large scale to meet its increasing demand. As a result of its increasing demand, scientists have also been able to develop special cement from rice husk. 

          Pure ghee and vanaspati ghee are a part of our daily food. Pure ghee is expensive while vanaspati ghee is comparatively cheaper. Because of this, pure ghee is often adulterated with vanaspati ghee and common consumers are cheated. Do you know how you can test the purity of pure ghee?

          Vanaspati ghee is manufactured by the hydrogenation of vegetable oils. In the process of hydrogenation, nickel powder is used as a catalyst and hydrogen is passed. By this process, unsaturated vegetable oils get saturated and are converted in what we call as vanaspati ghee. To test the presence of vanaspati ghee in pure ghee, we carry out the chemical test for nickel particles which are always present in traces in vanaspati ghee.

          To detect the presence of vanaspati ghee in pure ghee, we make use of hydrochloric acid and 2% solution of furfural in alcohol. These chemicals are easily available in the market.

          About 5 ml. sample of ghee is heated in a test tube. When it melts, about 5 ml. of hydrochloric acid is added to it. The tube is then shaken well. Now 5 to 6 drops of furfural solution are added and the test tube is again shaken well for four to five minutes. Now, if a pink colour develops, the ghee being tested is not pure. It means it contains vanaspati ghee, i.e. nickel particles. If there is no change in the colour, the ghee is pure. This system of detection is widely used by the ghee traders.

 

All elements are made up of tiny invisible particles called atoms. According to the scientists, at the centre of an atom there is a core called the nucleus around which the electrons revolve in different orbits. The nucleus is made up of two types of particles called protons and neutrons. All atoms of a particular element have the same number of protons in the nucleus. However, the number of neutrons in the nucleus can vary without changing the chemical nature of the element.

The number of protons in an atom is called its atomic number while the total number of protons and neutrons is called its mass number or atomic weight. Chemical properties of a substance depend upon the electrons outside the nucleus while the physical properties on its mass number. Atoms of the same element having the same atomic number but different mass numbers are called its isotopes. For example, hydrogen has three isotopes – protium, deuterium and tritium. Protium has only one proton, deuterium or heavy hydrogen has one proton and one neutron while tritium has one proton and two neutrons. Tritium does not exist naturally. It is produced by artificial means.

All the isotopes of the same element have the same chemical properties but different physical properties. Almost all elements are mixtures of isotopes. Oxygen and chlorine have two isotopes each. 

Isotopes of some elements are radioactive in nature, i.e. they emit invisible radiations and decay into isotopes of other elements. Isotopes of an element are separated by an instrument called mass spectograph. Particle accelerators are used to prepare ‘radio isotopes’.

Radio isotopes are very useful. Cobalt-60 and Radium isotopes are used to burn out cancerous growths. Carbon-14 is used to determine the age of the dead plants and animals. This process is called radioactive dating. Isotopes of iodine are used for the treatment of goitre. Artificial radio-isotopes are used to study the chemical reactions. They are also used as tracers to study the movements of compounds in plants and animals. With the help of isotopes many diseases are diagnosed. This branch of medicine is called nuclear medicine.

Manufacturers of precision instruments use some isotopes to detect tiny flaws in metal castings and to make extremely fine measurements.

 

          An alloy is an intimate mixture of two or more substances, at least one of which is a metal. The mixture is usually more useful than each ingredient on its own. Almost all alloys are made by mixing constituent elements in the required proportions in the molten state. Man has known a few alloys like brass and bronze since ancient times. Brass is an alloy of copper and zinc while bronze is an alloy of copper and tin.

          Most metals in their pure form are often too soft to be used for practical purposes. Their strength, ductility, hardness, melting point and colour can be improved by mixing one or more metals. For example, pure aluminium is light and weak but when copper and magnesium are added to it, its alloy becomes stronger. Copper and tin are soft and weak but when mixed together they become harder. Brass, a mixture of copper and zinc, is another strong and useful alloy. Mixture of lead and tin is used for soldering purposes. Alloys have more corrosion resistance and better casting properties than metals. 

          Today, the most important alloys are the alloys of steel. They are used for making different machine parts. Copper-nickel, bronze and aluminium alloys are used in minting coins, shipping and airplane industries. Lead alloys are used in the making of electrodes of storage batteries. Zinc alloys are used in the making of automobiles. Nickel-silver, an alloy of copper, nickel and zinc, is best known for its use in domestic cutlery. Expensive alloys of platinum, gold and silver are used in jewelry. Stainless steel, aluminium alloys, Nimonic alloys are 20th century alloys. Super alloys of tungsten and molybdenum are the development of recent years which have proved very useful in rocketry. Thus we see that alloys are very useful to us.

 

          Sulfa drugs are synthetic chemicals that are used to treat many diseases caused by bacteria. The first sulfa drug was developed by a German bacteriologist, Gerhard Domagk, in 1930. He showed through experiments that a sulfa drug called Prontosil could kill streptococcus bacteria. Sulfanilamide was the active chemical in Prontosil which killed the bacteria. Since that time, scientists have experimented with thousands of similar chemicals, but only about 20 of these are being used as medicines. 

          How do sulfa drugs control the bacterial diseases? Sulfa drugs operate by interfering with the normal metabolism of the bacteria cells. All living cells need folic acid to grow and reproduce. Human beings and many other animals get folic acid from their food. Bacteria, however, make their own folic acid. For this most bacteria need a chemical called para-amino benzoic acid (PABA). Chemically sulfa drugs and PABA are almost the same. The only difference between the two is that the sulfa drugs have sulphur atoms whereas PABA has carbon atoms. Bacteria cannot make out the difference between the two and absorb sulfa drug. This prevents the production of folic acid. Without folic acid bacteria cannot grow and reproduce. Thus, the sulfa drugs do not actually kill the bacteria, but keep them away from reproducing and allow the body’s own defence to kill them.

          Unfortunately, the sulfa drugs do not act on all the bacteria that cause diseases. However, they are very effective in the treatment of pneumonia and meningitis. They have little effect on tuberculosis bacteria. Moreover, they are toxic and cause many side-effects such as nausea and skin blisters. Although these medicines are found in common use but the antibiotics have been proved more effective. The sulfa drugs and antibiotics save thousands of lives every year, throughout the world.