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J. Perelman
"Entertaining physics". Book 2.
Chapter 7. Thermal phenomena

COLD FROM COAL

Receiving from coal is not heat, but the cold is not something unattainable: it everyday at plants of the so-called "dry ice". Coal is burned here in the boilers, and the resulting smoke is cleared, and the contained carbon dioxide is captured alkaline solution. Allocated then in pure form by heating the carbon dioxide with subsequent cooling and compressing means in a liquid state under a pressure of 70 atmospheres. This is the liquid carbon dioxide, which in thick-walled cylinders is delivered to the plants of fizzy drinks and is used for industrial needs. It is cold enough to freeze the ground, as was done in the construction of the Moscow metro; but for many purposes it is required to have carbon dioxide in solid form, what is called dry ice.

Dry ice, i.e., solid carbon dioxide, is obtained from the liquid during its rapid evaporation under reduced pressure. Pieces of dry ice in appearance resemble rather compacted snow than ice, and in many ways different from hard water. Carbon dioxide ice is heavier than ordinary ice and sinks in water. Despite the extremely low temperature (minus 78°), the cold is not felt by your fingers if you care to take a piece in hand: formed in contact with our body carbon dioxide protects the skin from the action of cold. Just squeezing the bar dry ice, we run the risk of frost bitten fingers.

The name "dry ice" extremely successfully underlines the main physical feature of the ice. He really never wet no and nothing moisturizes around him. Under the influence of heat it goes directly to a gas, bypassing the liquid state to exist in liquid form carbon dioxide under a pressure of one atmosphere cannot.

This feature of dry ice along with its low temperature makes it indispensable cooling substance for practical needs. Products that are stored with carbon dioxide ice, not only moisturized, but are protected from damage because the resulting carbon dioxide is the environment prevents the growth of microorganisms; therefore, the products do not appear mold and bacteria. Insects and rodents also can't live in this atmosphere. Finally, carbon dioxide is a reliable fire means: a few pieces of dry ice, thrown into the burning gasoline, extinguish fire. All this provided the dry ice is widely used in industry and household.

Entertaining physics J. Perelman

 




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