Category Science & Technology

          Normally if fresh milk is not boiled for sometime it becomes sour. But this does not happen with boiled milk for several hours. Do you know why it is so?

          Fresh milk contains several types of bacteria. When milk comes in contact with air, the number of the bacteria multiplies very fast. These bacteria turn the milk sour. The bacteria come to the milk from three different sources. First, if the cow or the buffalo from which the milk comes is suffering from some disease it might be excreting bacteria in its milk. The tuberculosis germs are transmitted from cattle to man in this way. Secondly, the milkman could have certain infectious disease and might contaminate the milk while milking the cow. Thirdly, the water used to wash the milk pot or the teats of the cow or buffalo may have germs in it. The bacteria transmitted to the milk from any of these three sources grow very fast and spoil the milk.

          Pasteurization is a process for sterilizing milk and other drinks invented by Louis Pasteur (1822-1895) – a French micro-biologist and chemist, for improving storage qualities and to protect them from spoiling. This method is named after him. The milk and butter sold in the market are normally first pasteurized, and then marketed.

          In the process of pasteurization, milk, wine, butter etc. are heated up to a certain temperature and then quickly chilled. This kills the bacteria in them. If milk is heated up to 63° for 30 minutes in between 72°- 85° for 16 seconds and then chilled to 10° or less, the bacteria present in it are destroyed. Pasteurization not only protects the milk from being spoiled but also kills the bacteria of tuberculosis and other diseases. Pasteurized milk can be kept unspoiled for a longer time without boiling. The process does not affect the taste of the milk.

          Nowadays gamma rays and beta rays are also being used for pasteurization. These rays kill the bacteria present in the milk and other drinks. 

          We know that the sunlight consists of all those colours which are seen in a rainbow. These colours are: violet, indigo, blue, green, yellow, orange and red. Light from the sun travels in the form of waves which are known as electromagnetic waves. The different colours of light have different wavelengths. Our eyes are sensitive only to the wavelengths relating to the above seven colours. Apart from the wavelengths of these seven colours, the sunlight consists of radiations of other wavelengths also, but our eyes are not sensitive to them. Rays having wavelengths higher than of red light are called infra-red rays and those lower than violet light are called ultraviolet rays. Both infra-red and ultraviolet rays are not visible to our eyes. 

          Infra-red rays come not only from the sun but from every hot object. Burning wood and coal, electric heater – all produce these rays. Infra-red rays were discovered by the British astronomer Sir William Herschel in 1800. In fact all objects give of infra-red rays according to their temperature. The warmer an object is, the more infra-red rays it gives off. These can be recorded on special type of photographic films made of infra-red sensitive materials. Whenever these rays fall on any material body they produce heat. They are very useful to us.

          Infra-red radiations are being used for the treatment of several diseases. Special types of infra-red lamps are used for treating the pains of muscles and joints – especially for back pain. They are also used for heating rooms in winter.

          Infra-red radiations are being used for the guidance and control of missiles and other ballistic weapons. These radiations are also used for transmitting and receiving invisible signals. Molecular structures are studied with the help of these radiations. Impurities present in the materials can also be detected by these rays. Infra-red absorption spectroscopy is an important analytical tool in organic chemistry.

 

          The number of naturally occurring stable elements on the earth is 92 only. Although scientists have so far discovered 107 elements in all, but 15 of these have been artificially made in the laboratories. These artificial elements are unstable in nature. The atoms of these 92 elements are also of 92 kinds only. Do you know how millions of substances are made from these elements?

          All substances available in the universe are made by the combination of atoms of these 92 elements. The atoms of different elements combine with one another in various proportions and keep on forming countless substances. Some of the important elements are: iron, gold, silver, copper, aluminium, sodium, potassium (metallic elements), oxygen, nitrogen, chlorine, carbon, sulphur (non-metallic elements). All the elements consist of atoms and the atoms of the same elements are alike. Two or more atoms combine with each other to make molecules. For example, two atoms of hydrogen combine with one atom of oxygen to make one molecule of water. Even a very small quantity of water consists of innumerable molecules. Similarly one atom of sodium combines with one atom of chlorine to make one molecule of the common salt sodium chloride. 

Continue reading “How are millions of substances made from only a few elements?”

          Whenever any substance is put in to fire it burns and changes into ash. But asbestos is one such material that does not burn in fire. That is why the fire fighters wear clothes made from asbestos when fighting large fires. In fact their clothes, shoes, gloves, helmets etc. are all made from the fibres of this material.

          Asbestos is a Greek word which means ‘inextinguishable’ or ‘unquenchable’. The invention of this material is not new. The Romans used asbestos sheets 2,000 years ago for wrapping dead bodies in order to preserve them.

          This material is obtained from mines. It is formed by the dissociation of olivine. Olivines are the silicates of calcium and magnesium. Due to certain chemical reactions in the mines, olivine changes into fibres of asbestos. Asbestos obtained from mines is first dried and then its fibres are separated with the help of machines. These fibres are woven into threads and ropes which are then used for making clothes, sheets, mats etc.

          Asbestos is a very useful material. It is used for making fire-proof clothes, paper and as heat-insulator in furnaces. It is also used for making fire proof tiles for buildings. In cold countries, water pipes coated with this material which serve as insulators preventing water from freezing in the pipes.

          It is a bad conductor of both heat and electricity and is least affected by acids and alkalies. It does not burn even at a temperature of 2000°C to 3000°C. Some special varieties of asbestos are now available which do not burn even at 5000°C. This variety is used in research laboratories. The most common mineral of asbestos is chrysotile found in Canada and Russia.

          Canada is credited with 75% of the total world production of asbestos. America manufactures maximum number of items from asbestos though the raw material obtained in this country is only 5%. 

          Pressure cooker is a modern kitchen appliance that can cook almost any type of food in a very short time. It also saves a lot of fuel. Moreover, the nutritional constituents of the food are also not spoilt. Do you know how the pressure cooker helps in fast cooking?

          We know that every liquid boils at a definite temperature at the normal atmospheric pressure. This temperature is called the ‘boiling point’ of the liquid. In the case of water it is 100° C. It is observed that with the increase of pressure, the boiling point of the liquid also increases. Similarly reduction in the pressure lowers its boiling point. It is this phenomenon that prompted the invention of pressure cooker. 

          Pressure cooker is essentially a vessel of stainless steel or an alloy of aluminium. It has a lid fitted with a safety valve at its top to let out the steam in order to maintain the internal pressure within the limit the vessel can bear. A rubber ring is fixed at the junction of the vessel and the lid which does not allow the steam to leak out. A thermally insulated handle is attached to the pressure cooker for handling it. The food to be cooked is put in the vessel along with some water and the lid is closed. When the vessel is heated, the steam so formed increases the pressure inside the vessel. As the pressure increases, the boiling point of water also increases and it reaches up to 130°C. This is why food gets cooked quickly inside the pressure cooker. When the steam pressure inside the cooker increases beyond the required pressure, the control valve is automatically lifted up, allowing the excess steam to escape. Thus the pressure inside is regulated and there is no risk of bursting.

          If there is no hissing or whistling after the cooker has been kept on the oven for a sufficient time, the valve should be slightly shaken to see if the hole below is not choked. Before opening the lid the valve should be slightly lifted up with the help of tongs to allow the steam to escape.