Litmus paper turns red when placed in an acid solution, but blue if the solution is alkaline. This absorbent paper is the oldest and most commonly used indicator of the presence of absence of acid. Its special qualities are due to the fact that it has been soaked and impregnated with a mixture of dyes called litmus. The litmus mixture …
Read More »When does apple scab occur?
Apple scab occurs when an apple tree falls victim to a fungus called Venturia Inaequalis, a malignant growth which slowly eats away at the leaves and fruits. It is a widespread and serious disease affecting apple trees all over the world, but is more powerful in warm climates. Farmers control the fungus by spraying the trees with sulphur. That is …
Read More »When does a tree stop growing?
A tree never permanently stops growing as long as it lives. But in most countries each year’s growth is ended during the cold and dry season. The annual period of growth depends on the climate. In most tropical regions a tree may grow continuously. Every period of growth is marked by an annual ring. This ring takes the form of …
Read More »When does a forest become petrified?
A forest becomes petrified or turned to stone under certain conditions, through the action over the centuries of water containing large quantities of minerals. Tree trunks buried ages ago under mud, sand or volcanic ash have been gradually transformed as water seeped into the empty cells of the decaying wood, filling them with mineral matter and preserving every detail of …
Read More »When does a car use overdrive?
A car uses overdrive when it is traveling at high speed over long distances. Overdrive, or cruising gear, is a device which enables the engine to run at a relatively low speed even when the vehicle is traveling fast. All internal combustion engines fitted in vehicles need some kind of gearbox because their efficiency at low speeds is poor. The …
Read More »When do plants breathe?
Plants breathe oxygen and carbon dioxide. In daylight they produce their own food at the same time by a process known as photosynthesis. During this process the plants release more oxygen into the atmosphere than they breathe in. The effect of the plant’s feeding and breathing system is that they exhale oxygen during the night. This is the reason for …
Read More »Life Of Ravan
Ravan is the primary antagonist in the Hindu epic Ramayana, where he is depicted as the king of Lanka. Rama had once addressed Ravan as a “Maha Brahman”. Ravan is depicted and described as having ten heads. He is described as a follower of Shiva, a great scholar, a capable ruler and a maestro of the veena, but someone who …
Read More »When did the first electric train appear?
The world’s first electric locomotive was designed by the German scientist Werner von Siemens. It was shown at an international trade exhibition in Berlin in 1879. A special track was built for the locomotive, which hauled up to thirty visitors at a time around the exhibition. One of earliest electric railway, in England was Volk’s Electric Railway, built along the …
Read More »When did talking movies start?
The first talking movies were produced in France before 1900 by Leon Caumont. They were short films, starring great performers such as Sarah Berhard, in which the movie pictures were synchronized with a gramophone record. By 1912 Eugene Lauste had discovered the basic method for recording sound on film, while Thomas Edison produced several one-reel talking pictures in the United …
Read More »When did mail coaches operate?
Regular mail coaches began to run in England in the 1780s. Armed guards travelled on them to protect them from highwaymen. By 1800 regular stage coach services were running between all the big towns and those carrying mails ran to a fast timetable. ‘Fast’ meant an average of 8 km an hour.
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