Category Chemistry

What is an aerosol?

An aerosol consists of fine particles of liquid or solid substances suspended in the air, or in any other gas. It is not, as many people think, merely a spray for use in applying paint easily, or getting rid of unpleasant smells.

      The germs of diseases, for example, are to be found suspended in the air, and these dangerous aerosols can be dealt with by spraying chemicals to form another aerosol which destroys the germs. Leaves of plants attacked by pests can be treated in the same way.

     Chemicals in the container part of an artificial aerosol spray are stored there under very high pressure. When the release trigger is pressed a valve opens, and the chemicals are forced out through a tiny hole in a fine spray. This invention is useful not only in the home, and to gardeners and doctors, but also to a wide variety of specialist users.

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When does copper turn green?

Although copper is highly resistant to the chemical action of the atmosphere and of sea water, it turns green if exposed to them for a long time. The colour is caused by the formation of a thin coating of green basic copper carbonate known as patina or verdigris. The latter name comes from the old French vert de Greece (green of Greece), but the reason for it is unknown. This beautiful green is often seen on copper roofs or statues, especially if they are near the sea.

     Copper was the first metal man learned to use. Five thousand years ago, when men discovered deposits of pure copper in what are now Iraq and Cyprus, they found that this fairly soft metal could be easily melted, cast in moulds and hammered into tools, weapons and ornaments.

      About half the copper produced today is used by the electrical industry. Pure copper is the best cheap conductor of electricity and can be drawn into threads one-thousandth of an inch thick.

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What is a glass made from?

Glass is made naturally from a fusion of silica (sand), soda and lime. This fusion can be achieved merely by lightning striking in a place where the right ingredients happen to be adjacent to each other. When glass is made by man, other ingredients are added, such as potash, lead oxide and boric oxide. Some of these ingredients are used to make glass clear, some to colour it, and others to give it a frosted effect.

      Glass was made by potters in Egypt for glazing stone beads as early as 12,000 B.C. As Egyptian culture progressed, craftsmen used glass for the manufacture of personal ornaments and bottles.

    A tremendous step forward in the use of glass was made by the Phoenicians in about 300 to 200 B.C. by the invention of the blow-pipe. The blowpipe is a hallow iron tube with a mouthpiece at one end and a knob shape at the other. The knob-shaped end is dipped into hot, viscous glass. A “gather” of molten glass can be blown by the worker into a hollow ball. The more he blows, the larger the ball.

    During the Roman civilization the art of glass-making reached near perfection. In the 3rd Century, the Romans cast glass on flat stones and produced the first window panes. The break-up of the Roman Empire and the ensuring Dark Ages brought an end to such cultural developments. The glazing of windows did not become wide spread over the whole of Europe until the 15th and 16th Centuries.

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Why does stainless steel resist rust?

Stainless steel resists rust because it contains a high proportion of chromium to carbon. Before the arrival of this alloy just before the First World War, Knives and other household articles made of steel easily rusted unless very carefully dried.

    It was an English researcher named Harry Brearley who discovered that rust was encouraged by the carbon in steel and other metals. The less carbon and the more chromium in steel, the better it would resist rust.

      But a careful balance had to be struck. Completely carbon-free steel was impossible to make, and only a limited amount of chromium could be included, because it tended to make steel brittle. Brearley discovered a satisfactionary formula only after many experiments.

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Why does an automobile have a carburetor?

An automobile is driven by an internal combustion engine which will work properly only if the right amounts of petrol and air are mixed together. The carburetor is the part of the engine where the mixing takes place.

     The burning of fuel in the engine is a chemical reaction in which petrol combines with the oxygen of the air to produce water, heat energy and oxides of carbon. A chemically correct mixture should have 15 parts of air to one part of petrol, both by weight. The amount of air then present is just sufficient to burn the petrol completely. If the engine uses a mixture with an excess of petrol a rich mixture-a small amount of unburnt petrol will be present in the exhaust fumes.

     A carburetor has to produce the required mixture to suit different engine conditions, such as starting, idling, acceleration, cruising and application of full power. It must be able to pass the correct mixture at all engine speeds and under varying loads, and has to atomize the petrol into tiny droplets and vaporize the resulting spray a combustible mixture.

     Inside the carburetor is a throttle valve which can increases or decreases the amount of mixture passing into the cylinders, which in turn control the power of the engine. This valve is mounted on a spindle which is operated by the accelerator pedal.

    A special device called a “strangler” or choke is also incorporated to help in starting the engine in cold weather by allowing an extra-rich mixture.

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What is plastic?

A plastic, in the modern sense of the word, is a synthetic or man-made material which can be formed into various shapes. The first plastic material was Celluloid, made in 1868 by an American, John W. Hyatt, by dissolving nitrocellulose under pressure.

      The use of plastic began slowly, but shortages of natural material caused by two world wars forced scientists to develop substitutes. Since the Second World War the making of plastics has become a gigantic industry, which has grown so fast that many people still have only a hazy idea what plastics are. In fact, the term “plastics” is as general as the word “metals”. The high-temperature cone of a rocket and the highly inflammable table-tennis ball are both plastics, just as lead and steel are both metals.

    However, all plastics have some things in common: first, they are entirely man-made and not found in nature; secondly, they consist of large molecules of an organic nature; thirdly, at some stage in their manufacture they are liquid and can be shaped; and fourthly, in their final state they are solid.

    Most of the raw materials for plastics are produced by the petroleum and coal industries. Scientists are able to produce different properties in plastics so that they can be used in a tremendous variety of articles.

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