Notes on the Text

1. Owing to the presence — благодаря присутствию

2. In terms of — на основании, исходя из...

TEXT. AIR Liquid Air

Liquid air is a mixture of the liquefied gases. It is a milky liquid owing to the presence of solid carbon dioxide and ice. If these solids were removed by filtering, the filtrate would have a pale blue tint.

Liquid air due to its extremely low temperature produces remarkable physical changes.

If a tin or iron vessel were cooled by liquid air, it would become so brittle that it could be crushed with the fingers.

Mercury freezes so hard in liquid air that it could be used as a hammer. It could be hardly crushed.

If the liquid air were in a tea kettle standing on a block oi ice, the liquid air would boil vigorously. If the kettle of liquid air’were placed over a lighted Bunsen burner, frost and ice would collect on the bottom of the kettle.

Ordinary liquid air is from one half to one fifth liquid oxygen, and therefore it can support combustion.

A red hot rod of steel would have burned brilliantly if it had been placed in the liquid air.

Lately numerous applications of liquid air have been pro­posed and have been used in all branches of life. For example, it can be used to remove diseased flesh from the wounds. It can be widely used as commercial source of oxygen and nitro­gen. Liquid air can be readily manufactured in large quanti­ties at a comparatively low cost, that is why liquid air is made use of both in industry and in everyday life.

Ordinary Air

Ordinary air contains nearly constant proportions of ;hree elementary substances, viz. nitrogen — 75.4 per cent, oxygen — 23.2 per cent and argon — 1.2 per cent by weight. It also contains small proportions of several inactive gases ind some proportions of carbon dioxide, water vapour and lust.

The relative proportion of water vapour in the air could зе stated in terms of relative humidity, i. e. the ratio between the concentration of water vapour in the air and the concent­ration required for equilibrium at the same temperature.

Remember the following words and word combinations:

carbon dioxide to crush

to remove (Ло-тъ frost _u

pale ^ " combus

tint Й f used to

low to freeze

remarkable vigorously

brittle

cost

to make use of * term . '

in terms of to require humid

humidity , i

ratio v-: -v*?;-V

If the relative humidity were low, evaporation would эссиг rapidly. If the relative humidity were high, evapora­tion would occur slowly as the air is nearly saturated.

Ex. 10. Answer the following questions:

1. What is liquid air? 2. What are the properties of liquid air? 3. What changes can liquid air produce? 4. When does an iron vessel become brittle? 5. What freezes hard in liquid air? 6. What do you know about ordinary liquid air? 7. Where is liquid air applied? 8. What does ordinary air contain? 9. When can evaporation occur rapidly? 10. What would happen if the relative humidity were high?

Ex. 11. Retell the text according to the following plan: