How do raw fruits become ripe when treated with chemicals?

The ripening signal of a fruit comes from a hormone ethylene. Production of ethylene turns on some genes that are transcribed and translated to produce other enzymes. These enzymes are responsible for the conversion of starch into simple sugar, degradation of chlorophyll and appearance of other new pigments like carotenoids, change in the skin colour and the breakdown of acid, making the fruit taste neutral.

Hardy nature of the skin loosens when pectin is broken-down by an enzyme pectinase. Conversion of larger molecules into smaller volatile substances causes an aromatic odour.

Natural process of fruit ripening is accelerated by using certain chemicals. Here, calcium carbide is used. When carbide is dissolved in water it produces acetylene, an analogue of ethylene, a natural fruit-ripening agent.

The ripening process is accelerated since acetylene imitates ethylene. Since the amount of carbide needed to ripen the immature fruit is more it makes the fruit become more tasteless and toxic. Presence of trace amount of arsenic and phosphorous in carbide makes the healthy fruits poisonous.

One can distinguish the artificially ripenened fruit by the uniform skin colour in fruits like tomato, mango, papaws, etc and in the case of banana, yellow colour fruit with dark green stem.


Why are diesel driven vehicles noisy?

Diesel engines are inherently noisy because of the auto-ignition of the initially formed mixture of fuel-vapour and air, which causes rapid rate of pressure rise producing the characteristic noise. This abnormality is due to the inborn feature of a diesel engine, which uses a high compression ratio to obtain high fuel efficiency and a high compression-temperature for ignition of the fuel injected into the cylinder at high pressure. In a diesel engine, unlike a petrol engine, the air and fuel do not mix outside the engine.

Air is compressed to a high compression ratio leading to high fuel efficiency, and also to a high compression temperature to initiate combustion. They just meet inside the combustion chamber for a brief period, while all the processes of mixture formation like fuel-jet break-up, evaporation and mixing should take place within a short time called ignition delay period. Combustion follows this after the initially formed fuel-air vapour auto-ignites with a noise, forming the sources of ignition (chemical spark plugs if you wish to call) for the bulk of the fuel remaining. Diesel engine can be made less noisy by using common rail high-pressure injection system and electronic control.



What causes milk to rise up when we boil it?

Milk contains 87 per cent water, 4 per cent proteins and 5 per cent lactose (milk sugar). When we boil milk, the fat, sugar, proteins and minerals get separated. Since they are lighter than milk they collect on the surface in the form of cream.

During heating some amount of water gets converted into vapour and the bubbles of water vapour rise to the top but the heat is conducted away by the layer of water and by the fat droplets that have a higher boiling point than water.

The vapour gets trapped in the creamy upper layer. As the milk is heated further the water vapour expands and thick foam is produced on the top.

As the milk is boiled continuously the water, which boils at 100 degrees Centigrade, produces more water vapour and pressure builds up in the boiling milk so that the vapour pressure raises the creamy layer. So the milk pushes the creamy layer out and milk spills out.

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"Life is either a daring adventure or nothing."
Helen Keller