Part 79

What Is a Molecule?

The word molecule means “smallest mass,” which indicates the very smallest division that can be made of any substance without destroying its identity. Every substance is made up of molecules, and in many cases the molecules of one substance will mix with those of another substance, while in other cases they will not. When you dissolve sugar in water or melt lead or change water into steam, the physical body of the substance is changed, but the molecules remain as they were. They are only changed in so far as their relations to each other and to those of another substance are concerned.

How Do We Know a Thing Is Solid, Liquid or Gas?

The relations of the molecules in any substance to each other is what determines whether a substance is a solid, a liquid or a gas. A gas is a substance in which the molecules are constantly moving rapidly about among each other, but always in straight lines. A liquid substance is one in which the molecules are also constantly moving about but which do not move in straight lines. Solids are substances in which the molecules stick together in one position by the power of cohesion which they have. Cohesion means the power of sticking together.

How Big Is a Molecule?

We do not as yet know all there is to be learned about molecules. We know through the wonders of chemistry that small as a molecule is, it is still made up of smaller particles called atoms. An atom is the smallest division of anything that can be imagined. We have found by chemistry that even a molecule is capable of being divided, i.e., it is made up of still smaller particles, but molecules are small enough. An eminent scientist, Sir William Thomson, has given us probably the nearest approach to a correct way of saying something of the size of a molecule. “If a drop of water were magnified to the size of the earth, the molecules would each occupy spaces greater than those filled by small shot and smaller than those occupied by cricket balls.”

To get at what water is made of we must separate it through chemistry into its parts or atoms. When we do this we find that a molecule of water is made of three atoms or parts. Two of these are exactly alike and consist of a gas called hydrogen, and the other part is another gas called oxygen, concerning which gases we have already learned much in the answers to other questions in this book. In other words, when we separate water, which is a liquid, into its parts, we change the relations of the molecules in the water which move in irregular lines, into parts which move in straight lines and, when the molecules of a substance, as we have already seen, move in straight lines, the substance becomes a gas. On the other hand, when you freeze water, it becomes a solid (ice), and in doing that you fix the molecules in the water so that they stick to each other.

Men thought for a long time that water was an element like oxygen and hydrogen, i. e., that its molecules could not be separated in its parts and was, therefore, considered one of the things which could not be divided up, but this was due to the fact that it requires a great amount of power to break up the molecules of water.

What Is an Element?

An element is any substance whose molecules cannot be broken up and made to form other substances. You can take one or more elements and make a compound, which is what water is. A compound is a substance in which the molecules are made up of at least two kinds of elements or elementary substances.

~THE DIFFERENCE BETWEEN ELEMENTS AND COMPOUNDS~

The things we find in the world are known as either compounds or elements. An element, as we have already learned, is something in which the molecules cannot be broken up. A compound is, therefore, a substance in which the molecules are made of molecules of one or more elements and is either gas, liquid or solid, according to the relations which these molecules have to each other. We have so far discovered less than eighty real elements in the world, although since we find a new one every little while, there are probably many more as yet undiscovered.

Not all elements are gases, of course. Solids like copper, gold, iron, lead and a number of others are elements. Among liquids we have mercury, and of the gases we find hydrogen, nitrogen and oxygen, which are the three wonderful gases about which we are about to learn something, and these three are also the world’s most important gases. Ammonia is an element, but, while we think of it as a liquid, the real ammonia is really a gas. Our household ammonia is really a compound of ammonia with something else.

What Is Hydrogen Gas?

Hydrogen is one of the elementary substances in the form of a gas. It has no color or taste or odor, so we can neither see, smell nor taste it. It is the lightest substance known to the world. We have by the aid of chemistry been able to catch and retain it in sufficient quantities to weigh it and have found it to be lighter than anything else in the world. It is soluble in water and some other liquids, but only slightly so. It refracts light very strongly and will absorb in a very remarkable manner with some metals when they are heated. It burns with a beautiful blue flame and very great heat. When burned it combines with oxygen in the air and forms water. Hydrogen is not poisonous but, if inhaled, it prevents the blood from securing oxygen, and so the inhaling of hydrogen will cause death. Hydrogen is not found free in the air except in small quantities like oxygen and nitrogen and is, therefore, secured by separating compounds by known methods. It can be secured by the action which diluted sulphuric acid has on zinc or iron, by passing steam through a red-hot tube filled with iron trimmings, by passing an electric current through water and in other ways. Hydrogen is absolutely necessary to every form of animal or vegetable structure. It is found in all acids.

What Is Oxygen?

Oxygen was discovered in 1774. It is an elementary substance in the form of a gas which is found free in the air. It is colorless, tasteless and odorless and, like hydrogen, cannot therefore be seen, tasted or smelled. It is soluble in water and combines very readily with most of the elements. In most cases when oxygen combines with other things the process of combining is so rapid that light and heat are produced--this combination is called combustion. Where the process of combining with other substances acts slowly the heat and light produced at one time are not enough to be noticed. Where metals tarnish or rust or animal or vegetable substances decay, the same thing chemically is taking place as when you light a fire and produce light or heat--you are making the oxygen combine with the substance in the material which is burning. When iron is rusting or vegetables decaying, the action is so slow that no heat or light is produced, but the result is the same if some outside force does not stop the action. The fire will burn until everything burnable which it can reach is burned out, and in the case of the piece of iron rusting, the action will go on slowly until the whole piece of iron is destroyed--or burned out. Like hydrogen, no vegetable or animal life can live without oxygen continually given it. Oxygen will destroy life and will sustain it.

All of our body heat and muscular energy are produced by slow combustion going on in all parts of the body, of oxygen carried in the blood after it enters the lungs. In sunlight oxygen is exhaled by growing plants.

Oxygen is the most widely distributed and abundant element in nature. It amounts to about one-fifth of the volume of the air belt of the earth; about ninety per cent of all the weight of water is oxygen. The rocks of the earth contain about fifty per cent of oxygen and it is found in most animal and vegetable products and in acids.

What Is Nitrogen?

Nitrogen is the third of the world’s wonderful and important gases. It is also without color, taste or smell. It will not burn or help other substances to burn and it will not combine easily with any other element. It will unite at a very high degree of heat with magnesium, silica, and other metals. About 7.7 per cent of the weight of the air is nitrogen, so that it is a very important part of the air we breathe and it is absolutely necessary in making all animal and vegetable tissues. When united with hydrogen, it produces ammonia, and with oxygen one of the most important acids--nitric acid. It is found free in the air and is thus easily secured. Nitrogen, while very important to all kinds of life, is known as the quiet gas. It stays quietly by itself unless forced to combine under great power with other things, and, even under those conditions, will combine rarely. We find a good deal of nitrogen in the blood but, while we need the nitrogen which is found in the blood, it does nothing particularly to the blood or the rest of the body. The nitrogen which the body uses is valuable to the body only when found in a compound. This nitrogen which the body needs is secured through vegetable products such as the wheat from which our bread is made, and which are said to secure their nitrogen through the aid of microbes which are able to force the nitrogen of the air into a compound. Some day perhaps we shall know all there is to know about nitrogen, which is the least known of these three wonderful and necessary gases.

Why Are Some Things Transparent and Others Not?

Transparency is produced by the way rays of light go through substances or not. When light strikes a substance that is almost perfectly transparent, it means that the rays of light go through it almost exactly as they come in. We think quickly of glass when we think of something readily transparent. Water is almost equally as transparent. When the sunlight is shining on one side of a pane of ordinary window glass, it causes every thing on that side of the window to reflect the light which strikes it in all directions. When these rays of light strike the window pane, they go right through and that is how we are able to see the trees and grass and everything else through a clear window pane. The same reason applies also to the water.

Some kinds of window glass (the frosted kind) we cannot see through--they are not transparent. The surface of a frosted window pane is so made that when the light rays strike it the rays are twisted and broken, and do not come through as they entered the glass.

Sometimes the water is almost perfectly transparent. When water is perfectly clear, it is quite transparent. When you look at or into water that is not transparent, you will know that there are particles of solid matter floating about in it which twist and mix the light rays. If the water is not too deep you can see the bottom sometimes even when there are some particles of solid substances floating about in it, but the deeper the water the more of these solid particles there are generally in it, so that it is impossible in most waters to see the bottom if the water is deep. In some places, however, the water is so free from floating particles that the bottom of the ocean can be seen at quite considerable depths.

Why Is the Sea Water Salt?

All water that comes into the oceans by way of the rivers and other streams contains salt. The amount is so very small for a given quantity of water that it cannot be tasted. But all this river water is poured into the oceans eventually at some point. After it reaches the oceans, the water is evaporated by the action of the sun. When the sun picks up the water in the form of moisture, it does not take up any of the solid substances which the water contained as it came in from the rivers, and while there is about as much water in the ocean all the time and about as much also in the air in the form of moisture also, the ocean never gets fuller; the solid substances from the river waters keep piling up in the ocean and float about in the water there. The salt which is in the river water has been left behind by the sun when it evaporated the water in the ocean for so long that the amount of salt has become very noticeable. The moisture which the sun takes into the air from the ocean is eventually turned back to the earth again in the form of rain. This process of evaporation and precipitation in the form of rain is going on all the time. When the water which is in the form of rain strikes the earth, it is pure water. It sinks into the ground and on the way picks up some salt, finds its way into a river sooner or later, and then evidently gets back into the ocean. All this time it has been carrying the tiny bit of salt which it picked up in going through the ground. But when it reaches the ocean again and is taken up by the sun, it leaves its salt behind and so the salt from countless drops of water is constantly being left in the ocean as it goes up into the air. This has been going on for countless ages and the amount of salt has been increasing in the ocean all the time, so that the sea is becoming saltier and saltier.

Why Does Salt Make Me Thirsty?