Percy Saltzman Essay: The Air About Us

Sunday December 16, 1951

(CBC Trans-Canada Network)
P. P. Saltzman,
Dominion Public Weather Service,

You can't see it, but it's all around you' it touches the floor and the ceiling and the walls; it's inside your mouth and between your fingers and way down in your toes. Sometimes it moves very fast; sometimes it stands quite still; sometimes it's warm and sometimes it's cold. You can't see it or taste it or smell it, but you can boil it and freeze it, squeeze it and weigh it, cut it with a knife and pour it uphill.

It's the air about us, and it's handy to have around.

It's a pity we can't see the air about us, for it we could, we wouldn't take it so much for granted. On the other hand, if air were visible, we'd hardly be able to see anything else.

We rarely give the air a second thought unless it's brought to our notice by force. A strong wind, for example, serves to remind us of its existence, or the appearance of a kit high in the sky, or a leaf gently fluttering to the ground. When the leaf floats down, it's the air under it that keeps it from falling fast. If there weren't any air, the leaf would fall like a rock.

Air is a definite object, just like a lump of coal, and has just as clear-cut characteristics. Just like a binful of coal has a certain size, shape and weight, a roomful of air also has a definite size, shape and weight. Take, for instance, the ordinary school classroom complete with pupils and all. Ask your friends how much the air in that room would weigh, and their guesses will probably range all the way from a fraction of an ounce to a pound or two. As a matter of fact, the air in the classroom would weigh about as much as the pupils in the room. This is a rough-and-ready reckoning, but it's near enough to emphasize the fact that most of us usually underestimate the weight of air.

The weight of a roomful of aire should not be confused with air pressure, which is due to the total weight of the air from the surface of the earth all the way up to the top of the atmosphere. This air pressure at sea level is about fifteen pounds per square inch, which works out to a about a ton per square foot.

Now, the surface area of the average human being is nearly seventeen square feet, which means that we go about carrying with us an air pressure of seventeen tons. Fortunately, this force isn't all exerted in a single direction or we'd soon be squashed flat. Actually, this fearful pressure of the air on us and around us is neatly balanced by an equal pressure under us and inside us, so that we move around happily unaware of the cross we bear.

Now, besides having weight, air has another definite characteristic, and that is that it holds and soaks up moisture like a sponge. Water vapour is constantly streaming into the atmosphere from the oceans and lakes and rivers, and is just as regularly being returned to the earth as rain and snow, or appearing as cloud and fog. A roomful of air at ordinary temperature holds about two quarts of water, which we could get if we compressed and cooled the air until it was thoroughly dry.

When air is compressed, it heats up, a fact easily verified every time a bicycle tire is pumped up by hand. The pump gets hot -- too hot often to be comfortable. What happens is that, in compressing the air, we squeeze it into a smaller space, causing the particles to collide with each other much more often than before, and these increased collisions are felt by us as heat. Now, if this heat is taken away and the air further compressed and then cooled again, it won't be long before we've turned the air into a liquid. This happens are the very low temperature of 220 degrees F below zero. Liquid air is pale blue and is quite unlike its warmer brother, the air around us. A fresh flower, thrust for an instant into liquid air, will come out frozen so solid that the slightest touch will crumble it into dust. Rubber balls, plunged momentarily into liquid air, become so brittle that, when dropped, they break into smithereens.

Now, ice is cold, but liquid air is colder, so that, compared to it, ice is boiling hot. So it is that liquid air, placed on a block of ice, will literally boil away with great clouds of steam, into the bargain.

As stated above, when a gas-like air is compressed it becomes hot; and the opposite is equally true. Compressed air, suddenly released from its container, will lose heat rapidly as it expands. This fact is made use of with other gases, as in our refrigeration systems, but I think it is most strikingly illustrated in southern Alberta at Hell's Kitchen. There, a vast pool of compressed gas lies deep under the earth, and it is drawn off into the open air by means of a long pipe. This gas is burned as waste, and the flames are so large and hot that it is necessary to shields one's face when in the vicinity. However, for some distance back of the flaming nozzle, the pip is covered by a thick sheath of ice, and this in the middle of summer. What has happened here is that the sudden release of pressure on the gas as it merges from below has cooled it and the pipe carrying it to well below the freezing point of water. The moisture of the air condensed out on the gas pipe and then froze solid, while only a few feet away a blazing inferno raged.

Air is the raw material of our weather. It brings us the rain and the snow, and wind and the cloud. We feel its strength in the gale at sea, measure its pressure with our barometers, and its temperatures with our thermometers. Our forecasters wage constant battle to keep up with its airy notions and commotions. Above all, it's handy to have around.