Tropical Hygiene – AIR

Air is the most important thing the body requires. A man can live some days without water, and some weeks without food, but cannot live five minutes with- out air. It is the first necessity of life.
Composition.-Air is a gas which is a mixture of other gases. These are Oxygen, Nitrogen and Carbon Dioxide. The proportions in which the chief gases are present in pure air may be taken as: Nitrogen 79 parts in every 100 parts.

Oxygen 21 parts in every 100 parts. Carbon Dioxide, a trace. Air also contains variable quantities of Water (in the form of vapour), Ammonia and, in certain districts, suspended matter.
Nitrogen. This forms the bulk of the air, practi- cally four parts out of five. It is a gas without colour, taste, or smell. It is of no use to the body and will not keep animals alive or even flames burning. A person who breathed pure nitrogen would die of suffocation, that is, of lack of oxygen; he would not be poisoned.

Oxygen. This forms one part in five of the air, and is the most important part of it for human and animal life. It has no colour, taste, or smell. It is the one gas necessary for all breathing and burning. If the air had more oxygen in it things would burn much more brightly and quickly, but nature has provided that the air should be diluted by nitrogen.
Carbon Dioxide. This is a colourless gas with a faint smell and taste. It is a heavy gas and will sink to the

bottom of a bottle containing it. It is therefore found in greater quantities near the ground than higher up in the air. It is often written CO, for short.
Carbon dioxide is produced in great quantities by three causes, Burning, Breathing and Decay. It is continually being put into the air. How is it then that the air does not gradually become full of carbon dioxide? Millions of people and animals are breathing it out and millions of fires and lamps are producing it. The explanation is that trees and all green plants make use of it. The gas (CO2) contains carbon and oxygen united together. By the action of sunlight and the green colouring matter of the leaves (chlorophyll) the carbon is separated from the oxygen. The plant keeps the carbon and makes food out of it but gets rid of the oxygen. Hence by the action of plant life, not only is carbon dioxide taken out of the air, but also the life-giving oxygen is given back in exchange. In this way the amount of CO2 is kept constant.

We may look upon the above gases, Nitrogen, Oxygen and Carbon Dioxide, as the ordinary parts of pure air. We have now to learn something about the other gases which are found in the air.
Water Vapour.-Water is always present in the air in the form of an invisible gas. The hotter it is the more water the air will hold.

To prove this obtain a glass of cold water. Soon you will notice a film of moisture form on the outside of the glass. This has come from the air. The air near the glass gets cold and cannot hold the water it held before. It therefore has to drop some. The air in the tropics is often very full of water and the above experiment is very easy to perform. If a glass of iced water is placed on a table-cloth the moisture in the air

GENERAL HYGIENE

settles so quickly on the outside of the glass that it runs down and wets the cloth.
Our comfort depends greatly upon the amount of moisture in the air. This is called the “humidity” of the air. Very humid air is uncomfortable.
Impurities.-The following impurities are sometimes found in air.ui mood vllaubsg Jon225obis d 90Ammonia. This is a gas which, when well diluted with air, has a rather pleasant smell. When dissolved in water it forms the Ammonia we can buy in the stores. It is a poison, but is never present in the air in sufficient quantities to harm anyone. But it does indicate a danger because it is produced by decaying animal and vegetable matter.

or more anodics ori Suspended Matter.-If a ray of sunlight is allowed to pass through a narrow opening into a dark room the air will be seen to be full of “motes”. These are little bits of dust which are too small to be seen under ordinary conditions. They may be either organic or mineral matter and may be dangerous to health. (Organic means animals or plants or matter formed by them. Mineral means any matter not formed by animal or plant life.) The organic matter may consist of germs of diseases, bits of skin off animals and men, or matter given off in the breath; and the mineral or inorganic matter may be particles of sand, dust, soot,

etc. blod lliw onla Impure Gases. These are usually found in districts where factories send their waste products into the air. They are also given off from swamps and mud banks in creeks and mangrove areas. In countries where coal gas is used for burning in houses the gas is sometimes found in the air because of leaking pipes. Coal gas contains a very poisonous gas called Carbon Monoxide (CO).

The Effect on Air of Breathing. We have seen that ordinary pure air has the following composition:
boing to Oxygen.
Nitrogen
Carbon Dioxide
Moisture.
21 per cent
79
trace
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variable
وو

Breathed out or expired air is composed as follows:
17 per cent
Oxygen.
Nitrogen.
Carbon Dioxide
Moisture.
Organic matter
79
4
وو
وو
دو
وو
saturated
traces

Noticing these figures we come to this conclusion:
1. The Nitrogen remains the same.
2. The Oxygen decreases.
3. The Carbon Dioxide increases.
In addition:
4. The temperature of the air is raised.
5. The expired air is full of moisture (saturated). 6. It contains now organic impurities thrown off by the lungs.
Let us notice one or two things:

(a) The oxygen gets less while the carbon dioxide increases. The explanation is as follows: In the body cells a process like burning takes place. The oxygen of the air is carried to the cells by the blood. It unites with the carbon in our food and forms carbon dioxide. This is sometimes expressed as: CO, CO,. The blood brings this CO, to the lungs to get rid of it.
(b) The temperature of the air is raised. Our bodies usually have a temperature between 98° and 99°, and expired air is raised to about 96°.
(c) The organic matter escaping from the lungs is another impurity produced by breathing. It may contain germs of disease.

GENERAL HYGIENE

(d) When you breathe on a piece of glass, moisture settles on it. The glass has been standing in ordinary air as the tumbler of iced water did; yet no water formed on it from the air until you breathed on it. This shows that there is more moisture in breathed-out air. There is as much moisture in it as it can hold; such air is then said to be ” saturated “. The moisture breathed out is the chief cause of stuffiness in a crowded room.

From the above we see that there is need to change the air of a room in order to keep it fit for us to breathe. Every breath spoils the air to some extent. A person who breathes air which has already been breathed does not get his fair share of life-giving oxygen, but gets more than his share of CO2 and organic matter and these do him harm.
It has been found that a man may breathe one part of CO2 in 100 parts of air without any bad effects, though more than this would give headache and make him drowsy. So we see that the gas is not very poisonous.
When, however, we examine air which has been

LIME WATER

Fig. 1.-CO, turns Lime Water milky.

breathed, we find that a man cannot breathe it without discomfort even when it is mixed with a good deal of fresh air. This is due to the fact that breathed air is warm and moist, and contains CO, and organic im- purities which, even if they come from healthy people, are bad to breathe into the lungs. Fainting, sickness, and headache produced by crowds are due not only to heat, moisture, and carbon dioxide, but also to fatigue and exhaustion.

The arranging of doors, windows and chimneys, so as to supply good air and remove bad, is called Ventilation. The amount of air which has to flow into a room ten feet high with a ten foot by ten foot floor with one person in it should be enough to fill the room again every twenty minutes. If there are four people in the room, they need a whole roomful of air every five minutes in a room of this size.

SOME EXPERIMENTS ON AIR

1. To test for Carbon Dioxide.-Place some clear lime water in a glass. With an enema syringe, pump air through this as follows:
Fig. 2.-To show CO, in Expired Air.

First pump ordinary air through it. As this con- tains only a trace of CO2 the lime water will not become cloudy unless the pumping is continued for a very long time.
Now burn a candle in another glass or mug, and pump the air from this vessel through the lime water. The lime water then turns milky. The milkiness is due to chalk which the CO, makes with the lime.

2. To show we breathe out Carbon Dioxide.-Blow into some clear lime water through a straw or other tube. The water turns milky.
3. To show the proportion of Oxygen in Air.-

Fig. 3.–(A) Phosphorus absorbing Oxygen.e (B) Water taking its place.

Obtain a glass tube about an inch wide and 2 or 3 feet long, corked at one end and closed at the other. Drop a piece of phosphorus into the tube and cork up. Gently warm the phosphorus which melts and absorbs the oxygen in the tube. Now place the tube upright in water and take out the cork under water. It will be found that the water will rise one-fifth of the tube to take the place of the oxygen. The gas left is nitrogen.

4. To prove Air has Weight. Take a glass round- bottomed flask containing a little water. Fit in a cork with a short glass tube inserted through it. Fix on a piece of rubber tubing, as shown in sketch. Have a rubber tubing clip ready. Boil the water to drive out the air. Then clip the tube. Now weigh the flask. This gives the weight of the flask and water. When cool, open the clip. Air rushes in and fills the flask. Weigh again. The weight will have increased owing to the air admitted, proving air has weight.
We know that air has weight when we feel the force of the wind. It is the weight of the air which makes it possible for birds and aeroplanes to fly in it.

 

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