simple science

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Simple Science

31. Climate
Other Facts about Heat:
Water, in freezing, loses heat, even though its temperature remains at 0 C. Because water loses heat when it freezes, the presence of large streams of water greatly influences the climate of a region. In winter the heat from the freezing water keeps the temperature of the surrounding higher than it would naturally be, and consequently the cold weather is less severe. In summer water evaporates, heat is taken from the air, and consequently the warm weather is less intense.
32. Molding of Glass and Forging of Iron
Other Facts about Heat:
The fire which is hot enough to melt a lump of ice may not be hot enough to melt an iron poker; on the other hand, it may be sufficiently hot to melt a tin spoon. Different substances melt, or liquefy, at different temperatures; for example, ice melts at 0 C., and tin at 233 C., while iron requires the relatively high temperature of 1200 C. Most substances have a definite melting or freezing point which never changes so long as the surrounding conditions remain the same.

But while most substances have a definite melting point, some substances do not. If a glass rod is held in a Bunsen burner, it will gradually grow softer and softer, and finally a drop of molten glass will fall from the end of the rod into the fire. The glass did not suddenly become a liquid at a definite temperature; instead it softened gradually, and then melted. While glass is in the soft, yielding, pliable state, it is molded into dishes, bottles, and other useful objects, such as lamp shades, globes, etc.. If glass melted at a definite temperature, it could not be molded in this way. Iron acts in a similar manner, and because of this property the blacksmith can shape his horseshoes, and the workman can make his engines and other articles of daily service to man.

FIG. - Molten glass being rolled into a form suitable for window panes.
33. Strange Behavior of Water
Other Facts about Heat:
One has but to remember that bottles of water burst when they freeze, and that ice floats on water like wood, to know that water expands on freezing or on solidifying. A quantity of water which occupies 100 cubic feet of space will, on becoming ice, need 109 cubic feet of space. On a cold winter night the water sometimes freezes in the water pipes, and the pipes burst. Water is very peculiar in expanding on solidification, because most substances contract on solidifying; gelatin and jelly, for example, contract so much that they shrink from the sides of the dish which contains them.

If water contracted in freezing, ice would be heavier than water and would sink in ponds and lakes as fast as it formed, and our streams and ponds would become masses of solid ice, killing all animal and plant life. But the ice is lighter than water and floats on top, and animals in the water beneath are as free to live and swim as they were in the warm sunny days of summer. The most severe winter cannot freeze a deep lake solid, and in the coldest weather a hole made in the ice will show water beneath the surface. Our ice boats cut and break the ice of the river, and through the water beneath our boats daily ply their way to and fro, independent of winter and its blighting blasts.

While most of us are familiar with the bursting of water pipes on a cold night, few of us realize the influence which freezing water exerts on the character of the land around us.

Water sinks into the ground and, on the approach of winter, freezes, expanding about one tenth of its volume; the expanding ice pushes the earth aside, the force in some cases being sufficient to dislodge even huge rocks. In the early days in New England it was said by the farmers that "rocks grew," because fields cleared of stones in the fall became rock covered with the approach of spring; the rocks and stones hidden underground and unseen in the fall were forced to the surface by the winter's expansion. We have all seen fence posts and bricks pushed out of place because of the heaving of the soil beneath them. Often householders must relay their pavements and walks because of the damage done by freezing water.

The most conspicuous effect of the expansive power of freezing water is seen in rocky or mountainous regions. Water easily finds entrance into the cracks and crevices of the rocks, where it lodges until frozen; then it expands and acts like a wedge, widening cracks, chiseling off edges, and even breaking rocks asunder. In regions where frequent frosts occur, the destructive action of water works constant changes in the appearance of the land; small cracks and crevices are enlarged, massive rocks are pried up out of position, huge slabs are split off, and particles large and small are forced from the parent rock. The greater part of the debris and rubbish brought down from the mountain slopes by the spring rains owes its origin to the fact that water expands when it freezes.

FIG. - The destruction caused by freezing water.
34. Heat Necessary to Dissolve a Substance
Other Facts about Heat:
It requires heat to dissolve any substance, just as it requires heat to change ice to water. If a handful of common salt is placed in a small cup of water and stirred with a thermometer, the temperature of the mixture falls several degrees. This is just what one would expect, because the heat needed to liquefy the salt must come from somewhere, and naturally it comes from the water, thereby lowering the temperature of the water. We know very well that potatoes cease boiling if a pinch of salt is put in the water; this is because the temperature of the water has been lowered by the amount of heat necessary to dissolve the salt.

Let some snow or chopped ice be placed in a vessel and mixed with one third its weight of coarse salt; if then a small tube of cold water is placed in this mixture, the water in the test tube will soon freeze solid. As soon as the snow and salt are mixed they melt. The heat necessary for this comes in part from the air and in part from the water in the test tube, and the water in the tube becomes in consequence cold enough to freeze. But the salt mixture does not freeze because its freezing point is far below that of pure water. The use of salt and ice in ice-cream freezers is a practical application of this principle. The heat necessary for melting the mixture of salt and ice is taken from the cream which thus becomes cold enough to freeze.
35. Why Things Burn
Burning or Oxidation:
The heat of our bodies comes from the food we eat; the heat for cooking and for warming our houses comes from coal. The production of heat through the burning of coal, or oil, or gas, or wood, is called combustion. Combustion cannot occur without the presence of a substance called oxygen, which exists rather abundantly in the air; that is, one fifth of our atmosphere consists of this substance which we call oxygen. We throw open our windows to allow fresh air to enter, and we take walks in order to breathe the pure air into our lungs. What we need for the energy and warmth of our bodies is the oxygen in the air. Whether we burn gas or wood or coal, the heat which is produced comes from the power which these various substances possess to combine with oxygen. We open the draft of a stove that it may "draw well": that it may secure oxygen for burning. We throw a blanket over burning material to smother the fire: to keep oxygen away from it. Burning, or oxidation, is combining with oxygen, and the more oxygen you add to a fire, the hotter the fire will burn, and the faster. The effect of oxygen on combustion may be clearly seen by thrusting a smoldering splinter into a jar containing oxygen; the smoldering splinter will instantly flare and blaze, while if it is removed from the jar, it loses its flame and again burns quietly. Oxygen for this experiment can be produced in the following way.
36. How to Prepare Oxygen
Burning or Oxidation:
Mix a small quantity of potassium chlorate with an equal amount of manganese dioxide and place the mixture in a strong test tube. Close the mouth of the tube with a one-hole rubber stopper in which is fitted a long, narrow tube, and clamp the test tube to an iron support, as shown in Figure. Fill the trough with water until the shelf is just covered and allow the end of the delivery tube to rest just beneath the hole in the shelf. Fill a medium-sized bottle with water, cover it with a glass plate, invert the bottle in the trough, and then remove the glass plate. Heat the test tube very gently, and when gas bubbles out of the tube, slip the bottle over the opening in the shelf, so that the tube runs into the bottle. The gas will force out the water and will finally fill the bottle. When all the water has been forced out, slip the glass plate under the mouth of the bottle and remove the bottle from the trough. The gas in the bottle is oxygen.

Everywhere in a large city or in a small village, smoke is seen, indicating the presence of fire; hence there must exist a large supply of oxygen to keep all the fires alive. The supply of oxygen needed for the fires of the world comes largely from the atmosphere.

FIG. - Preparing oxygen from potassium chlorate and manganese dioxide.
37. Matches
Burning or Oxidation:
The burning material is ordinarily set on fire by matches, thin strips of wood tipped with sulphur or phosphorus, or both. Phosphorus can unite with oxygen at a fairly low temperature, and if phosphorus is rubbed against a rough surface, the friction produced will raise the temperature of the phosphorus to a point where it can combine with oxygen. The burning phosphorus kindles the wood of the match, and from the burning match the fire is kindled. If you want to convince yourself that friction produces heat, rub a cent vigorously against your coat and note that the cent becomes warm. Matches have been in use less than a hundred years. Primitive man kindled his camp fire by rubbing pieces of dry wood together until they took fire, and this method is said to be used among some isolated distant tribes at the present time. A later and easier way was to strike flint and steel together and to catch the spark thus produced on tinder or dry fungus. Within the memory of some persons now living, the tinder box was a valuable asset to the home, particularly in the pioneer regions of the West.
38. Safety Matches
Burning or Oxidation:
Ordinary phosphorus, while excellent as a fire-producing material, is dangerously poisonous, and those to whom the dipping of wooden strips into phosphorus is a daily occupation suffer with a terrible disease which usually attacks the teeth and bones of the jaw. The teeth rot and fall out, abscesses form, and bones and flesh begin to decay; the only way to prevent the spread of the disease is to remove the affected bone, and in some instances it has been necessary to remove the entire jaw. Then, too, matches made of yellow or white phosphorus ignite easily, and, when rubbed against any rough surface, are apt to take fire. Many destructive fires have been started by the accidental friction of such matches against rough surfaces.

For these reasons the introduction of the so-called safety match was an important event. When common phosphorus, in the dangerous and easily ignited form, is heated in a closed vessel to about 250 C., it gradually changes to a harmless red mass. The red phosphorus is not only harmless, but it is difficult to ignite, and, in order to be ignited by friction, must be rubbed on a surface rich in oxygen. The head of a safety match is coated with a mixture of glue and oxygen-containing compounds; the surface on which the match is to be rubbed is coated with a mixture of red phosphorus and glue, to which finely powdered glass is sometimes added in order to increase the friction. Unless the head of the match is rubbed on the prepared phosphorus coating, ignition does not occur, and accidental fires are avoided.

Various kinds of safety matches have been manufactured in the last few years, but they are somewhat more expensive than the ordinary form, and hence manufacturers are reluctant to substitute them for the cheaper matches. Some foreign countries, such as Switzerland, prohibit the sale of the dangerous type, and it is hoped that the United States will soon follow the lead of these countries in demanding the sale of safety matches only.
39. Some Unfamiliar Forms of Burning
Burning or Oxidation:
While most of us think of burning as a process in which flames and smoke occur, there are in reality many modes of burning accompanied by neither flame nor smoke. Iron, for example, burns when it rusts, because it slowly combines with the oxygen of the air and is transformed into new substances. When the air is dry, iron does not unite with oxygen, but when moisture is present in the air, the iron unites with the oxygen and turns into iron rust. The burning is slow and unaccompanied by the fire and smoke so familiar to us, but the process is none the less burning, or combination with oxygen. Burning which is not accompanied by any of the appearances of ordinary burning is known as oxidation.

The tendency of iron to rust lessens its efficiency and value, and many devices have been introduced to prevent rusting. A coating of paint or varnish is sometimes applied to iron in order to prevent contact with air. The galvanizing of iron is another attempt to secure the same result; in this process iron is dipped into molten zinc, thereby acquiring a coating of zinc, and forming what is known as galvanized iron. Zinc does not combine with oxygen under ordinary circumstances, and hence galvanized iron is immune from rust.

Decay is a process of oxidation; the tree which rots slowly away is undergoing oxidation, and the result of the slow burning is the decomposed matter which we see and the invisible gases which pass into the atmosphere. The log which blazes on our hearth gives out sufficient heat to warm us; the log which decays in the forest gives out an equivalent amount of heat, but the heat is evolved so slowly that we are not conscious of it. Burning accompanied by a blaze and intense heat is a rapid process; burning unaccompanied by fire and appreciable heat is a slow, gradual process, requiring days, weeks, and even long years for its completion.

Another form of oxidation occurs daily in the human body. In Section 35 we saw that the human body is an engine whose fuel is food; the burning of that food in the body furnishes the heat necessary for bodily warmth and the energy required for thought and action. Oxygen is essential to burning, and the food fires within the body are kept alive by the oxygen taken into the body at every breath by the lungs. We see now one reason for an abundance of fresh air in daily life.
40. How to Breathe
Burning or Oxidation:
Air, which is essential to life and health, should enter the body through the nose and not through the mouth. The peculiar nature and arrangement of the membranes of the nose enable the nostrils to clean, and warm, and moisten the air which passes through them to the lungs. Floating around in the atmosphere are dust particles which ought not to get into the lungs. The nose is provided with small hairs and a moist inner membrane which serve as filters in removing solid particles from the air, and in thus purifying it before its entrance into the lungs.

In the immediate neighborhood of three Philadelphia high schools, having an approximate enrollment of over 8000 pupils, is a huge manufacturing plant which day and night pours forth grimy smoke and soot into the atmosphere which must supply oxygen to this vast group of young lives. If the vital importance of nose breathing is impressed upon these young people, the harmful effect of the foul air may be greatly lessened, the smoke particles and germs being held back by the nose filters and never reaching the lungs. If, however, this principle of hygiene is not brought to their attention, the dangerous habit of breathing through the open, or at least partially open, mouth will continue, and objectionable matter will pass through the mouth and find a lodging place in the lungs.

There is another very important reason why nose breathing is preferable to mouth breathing. The temperature of the human body is approximately 98 F., and the air which enters the lungs should not be far below this temperature. If air reaches the lungs through the nose, its journey is relatively long and slow, and there is opportunity for it to be warmed before it reaches the lungs. If, on the other hand, air passes to the lungs by way of the mouth, the warming process is brief and insufficient, and the lungs suffer in consequence. Naturally, the gravest danger is in winter.


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