Category Chemistry

How are different dyes made?

        Dyes are colour substances which impart their colour to the fabrics on which they are applied and for which they have a chemical affinity.

          Until the middle of the last century, the only dyes available were natural products obtained mostly from plants and flowers. Their range was limited. These natural dyes included: woad, a blue dye obtained from the plant woad; indigo, another blue dye from a plant. Some other dyes such as madder (red) safflower and turmeric (yellow) were extracted from certain kinds of sea-snails.

          The most important breakthrough in this field was made in 1856 with the discovery of the first synthetic dye by William Henry Perkin. This was mauveine, a bluish-purple dye discovered accidentally by William Perkin during experiments aimed at synthesizing the drug quinine. After this discovery, efforts were made to develop dyes from coal tar. As a result of these efforts, several thousand dyes were synthesized subsequently.

          These synthetic dyes were satisfactory when used with animal fibres such as wool, but they were easily washed off from vegetable fibres like cotton. This difficulty was overcome by treating the fibres with metal salts or with solutions of these salts in tannic acid before dyeing.

          After these dyes a large number of azo dyes were developed. Azo dyes are two component dyes used for cellulose fibres. The material is first treated with one component, and then put in the solution of the other component. The two components react to produce a dye within the fibres themselves. These dyes are highly resistant to washing.

          Another group of very stable dyes used for cellulose fibres is known as Vat dyes. These dyes, which include synthetic indigo used for dyeing blue denim, are mixed with chemicals to make them soluble for the dyeing process. After the material has been dyed, it is treated with other chemicals to make it more stable.

          Today we have a large number of synthetic dyes obtained from coal tar or petroleum products which are not only used to colour textiles, but also plastics, paper, leather, fur, oil, rubber, soap, food, cosmetics, ink and metal surfaces. 

What is dry cleaning?

Man has been using soap and water as cleaning agents for thousands of years. The first soap was made in the middle east about 5000 years ago. The discovery of soap less detergents is not very old. The first synthetic detergent was not invented until 1916, but since then the manufacture of non – soap detergents became a major development of the petrochemical industry. New methods of fabric cleaning came into use, such as dry cleaning.

Dry cleaning is a method of cleaning fabrics with chemical solvents instead of soap and water. Many of these solvents are derivatives of crude oil. Petrol is the most important of them. Benzene is also used in dry cleaning. Their fumes can be dangerous if inhaled and they catch fire easily. Some safer synthetic chemicals such as polychloroalkanes and alkanes have also been developed. The most common dry cleaning chemicals are carbon tetrachloride and trichloro ethylene.

In a dry cleaning establishment, clothes are usually treated first for stains. Then they are placed in the dry-cleaning machine with the cleaning fluid or solvent and tumbled slowly for up to half an hour. After a rinse in clean fluid, the clothes are spun around rapidly to extract the liquid, and are finally fluffed in hot air. Any stains remaining are removed by hand and clothes and then steam pressed.

Dry cleaning has several advantages over ordinary soap cleaning. Cleaning fluids can dissolve stains (especially oil and grease) which soap and detergents cannot remove. The process is most useful for delicate or expensive silken and woollen fabrics because it does not have any undesirable effect on them. For instance, the colours do not fade, as they might in water. 

What is quartz?

          Quartz is a hard, glossy mineral made of silicon and oxygen. It is found in most kinds of rocks in colourless, often transparent form. There are also coloured varieties including semi-precious stones such as amethyst and citrine. Pure quartz is called rock crystal also. In appearance it looks like glass. It has six sided crystalline structure. It ranks 7 on the Mohs’ scale of hardness and is resistant to chemical or mechanical breakdown.

          Quartz is extremely hard and will scratch glass. It melts at a very high temperature. It can be made into tubes, sheets or blocks. It can also be blown into various shapes by using oxy-hydrogen flame.

          Quartz has great economic importance. Sandstone, composed mainly of quartz, is an important building stone. Large amount of quartz sand is used in the manufacture of glass and porcelain and in metal casting for foundry moulds. Quartz is used as an abrasive in sandpaper and grindstones. It is used to make prisms and lenses which can transmit ultra-violet light. Tubing and various vessels of fused quartz have important laboratory application. It is also used in ornamental work and industry where its reaction to electricity makes it valuable in electronic instruments. Quartz fibres are used in extremely sensitive weighing devices.

          Quartz is a piezoelectric material, i.e. when pressure is applied across the two surfaces of a quartz crystal, an electric voltage develops across the crystal and when voltage is applied across the two faces of the crystal, and it expands, or contracts. Due to this property, it can help to change electric signals into sound waves and vice versa. The piezoelectric property of quartz plays an important role in radios, television and radar. Quartz oscillators are used in Quartz crystal watches to give accurate time.

          Natural quartz crystals of commercial grade are obtained from Brazil. Quartz can also be made synthetically.

 

What is a Mass Spectrograph?

               A mass spectrograph is an instrument used to analyze the constituents of substances. It not only detects different kinds of atoms and molecules present in the substance, but also finds out their relative amounts. By the use of electric and magnetic fields, it separates ions of different masses. Do you know how this instrument works?

               The working of the mass spectrograph first involves the change of the substance into a gas, which is passed into a vacuum chamber. A beam of electrons is bombarded to change the gas atoms and molecules into ions. The ions are then accelerated, by passing them through an electric field. Then the ions are passed through a magnetic field, where they get deflected. The positive ions are deflected one way, and the negative ions in the opposite direction. The amount of deflection is inversely proportional to the masses of the ions. The heavier the mass, the lesser the deflection. This separates ions of different masses. Ions of the same mass and charge stay together. The ions are then allowed to fall on a photographic plate. Different ions hit the plate at different places and as a result, this photographic plate records the amounts of various atoms and molecules. Photographic plate is used to identify different ions which have hit it. From the intensity variations on the plate, we can know the relative amounts of atoms or molecules present in the substance. 

               The mass spectrograph was developed by a British scientist, William Francis Aston. He was awarded the Nobel Prize in 1922 for this invention. After this, several other mass spectrographs were developed by many leading scientists like Dempster, Bainbridge, Nier, etc but all were just modifications of Aston’s mass spectrograph.

              The mass spectrograph is widely used in geology, chemistry, biology and nuclear physics. It is a very useful instrument for isotopic studies. Aston himself discovered 212 of the 287 naturally occurring isotopes. Mass spectrographs are also used as vacuum leak detectors.

 

How can we extinguish fires?

          We are all aware of the damage and disaster a fire can cause in certain situations. Now let us see how to control a fire and prevent it from spreading.

          A fire is basically a chemical reaction during which heat and light are produced. Three factors are necessary for a fire to start – fuel, oxygen or air, and heat to raise the temperature of the fuel to its ignition temperature.

          A fire can be extinguished when one or more of these agents is removed, i.e. fuel, supply of air and lowering the temperature of the combustible substance. All fire extinguishing methods make use of these principles.

          The original fire extinguisher, a bucket of water, is still useful in controlling many types of fires. The principal effect of water on a fire is to cool the burning material, thus removing the heat – one of the factors without which combustion cannot continue. It can be applied in a variety of ways such as by flooding the fire with water. Jets of water are used to knock down the flames of fire, and sprays are used to absorb heat and drive back smoke and gases.

           Another common extinguisher is the soda-acid type. It sprays a mixture of water and carbon dioxide on the fire. This is based upon the principle of cooling the burning material and cutting the supply of air by non-combustible carbon-dioxide.

           In this extinguisher a solution of sodium bicarbonate is placed in a cylindrical vessel of steel. Sulphuric acid is kept in a bottle in a small compartment made within the cylinder, near the top. When required, the knob is hit against the floor. This brings the sodium bicarbonate and sulphuric acid in contact with each other. Immediately carbon dioxide is formed and it comes out of the fire nozzle which is directed towards the fire. These extinguishers are useful only for small and localized fires. They are not effective against gasoline, oil and electrical fires.

           Foam extinguishers are based upon the principle of cutting off the supply of air by forming a fire-proof coating of foam around the burning material. In this, a mixture of sodium bicarbonate and aluminium sulphate containing licorice extract is sprayed. It produces foam and extinguishes the fire.

           The other types of extinguishers that are used on oil and electrical fires are: Carbon dioxide extinguishers, dry-chemical extinguishers and vaporizing liquid extinguishers.

           Water should never be used for extinguishing electrical or oil fires. In case of electrical fires, it can cause electrocution. If water is used on burning oil, the oil simply floats on top of water and continues to burn. As the water flows away, it can carry the oil with it and so spread the fire.

           Fire extinguishers are provided by law in all public buildings, factories and schools. Most of the big cities have fire brigades for fire prevention and control.

 

What is Heavy Water?

          We know that ordinary water is a compound of hydrogen and oxygen. It has two atoms of hydrogen and one atom of oxygen. Heavy water is a compound of deuterium (an isotope of hydrogen) and oxygen.

          In fact, hydrogen has three isotopes: protium (ordinary hydrogen), deuterium (heavy hydrogen) and tritium. Protium nucleus contains only one proton, while deuterium nucleus contains one proton and one neutron and the tritium nucleus contains one proton and two neutrons. Naturally occurring hydrogen contains 99.985% of protium, about .015% deuterium and about 1 part in tritium. Tritium is radioactive in nature. When deuterium combines with oxygen, it gives heavy water or deuterium oxide.

       

Continue reading “What is Heavy Water?”