Part 25

The answer is yes. It is harder to stop a train than to start it, or rather it takes more power. The speed of a train depends upon the motive power. When a train is stopped and you wish to start it, you must apply enough motive power to start it going. There must be enough power to move the weight of the train and overcome the friction of the wheels on the track. It is, of course, easier to move a thing that weighs less than a heavier one. If you throw a ball ten feet into the air, it will perhaps not sting your hand when you catch it on its return; but, if you throw it one hundred feet into the air, it will sting your hands when you catch it. Besides, it will come down faster the last ten feet of the way than the ball which you threw only ten feet into the air. This is because when movement is applied to anything you add power to it. The ball which comes down from one hundred feet in the air acquires more power in falling and it takes more power to stop it. A train in motion has not only the power of the weight of the train behind it, but also the additional weight which the movement of the train has given it. Therefore, it takes more power to stop it than to start it. To stop a train you must apply the same amount of power as is in the moving train because the power to stop any moving thing must always be at least as great as the power which is moving it.

What Makes the Knots In Boards?

We find knots in the boards which we notice in a lumber pile or in any other place where boards happen to be, because the smaller limbs which grow away from the larger limbs of trees grow from the inside as well as the outside of the tree.

When you see a knot in a board it means that before the tree was cut down and the log sawed up into boards, a limb was growing out from the inside of the tree at the spot where the knot occurs.

You will also find that the wood in the knot is harder generally than the rest of the board. This is because more strength is required at the base of a limb and in the part of the limb which grew inside the tree than in other parts, for the limb must be strong enough to support not only the limb itself, but also the smaller limbs which grow out of it.

How Many Stars Are There?

Man may never know how many stars there are. The best we can do is to figure on the number that can be seen with the largest telescopes which have been invented, for, of course, you know there must be many millions of them which to us are invisible. We have counted the stars so far as we can see them; or, rather, so far as we can photograph them. Astronomers have found that a photographic plate exposed to the stars will show more of them than can be seen by the naked eye. This is because the materials on a photographic plate are more sensitive to the light of the stars than the human eye. By this method man has been able in a way to count the stars he can see. It adds up to more than a hundred million of them. Astronomers found this out by taking photographs of the heavens at night, devoting one picture to each section, until the entire heavens had been covered, and then counting them.

[Illustration: WHERE PAINT COMES FROM

MAKING LEAD BUCKLES--THE FIRST STEP IN PAINT MAKING.]

The Story in a Can of Paint

Paint such as is most frequently used is the material used for painting buildings, such as houses, barns, stores, and many others which we need not mention here. This paint is used on these buildings mostly for two very important reasons--one being to beautify the buildings, the other being to protect them from the ravages of the weather, much in the same way that your clothes protect you from the weather.

Paint such as we mention here may be regarded as the most simple and useful form. You have no doubt frequently seen the painter-man spreading paint on some building, or perchance, you have seen your father doing it, and have noticed that paint is a fluid substance looking something like cream, which is applied to the surface to be painted with a suitable brush and is brushed out smoothly. After the first coat is dry, other coats are put on in the same way until enough paint has been put on to thoroughly hide the unevenness of the lumber and making it of a uniform color.

This paint is made by simply mixing together dry powder, which is usually called pigment, with a thin, yellowish liquid which is called linseed oil. In the earlier days, the painter-man mixed this paint himself whenever he desired to use it. In these more modern times, he usually buys this paint already prepared.

Perhaps a little history of the preparation of the package of a can of paint which he buys may be interesting to you.

Let us imagine that the can of paint is white. In this case, the pigment which is used is a white powder and is made of either metallic lead or metallic zinc. The preparation of this fine white powder is very interesting and requires considerable time to perfect.

Let us consider the pigment known as white lead first. This is produced by causing metallic lead, which is of a bluish-gray color and very heavy, to change from its original form by a process which is known as “corrosion.” This corrosion is brought about by first taking the metallic lead, which at this stage exists in large pieces known as “pigs.” These pigs of lead are melted in a furnace and then molded into small, thin shapes which are buckles.

[Illustration: HOW WHITE LEAD IS MADE

FILLING THE STACK WITH LEAD BUCKLES.]

[Illustration: LEAD BEING TAKEN OUT OF THE STACKS.

The next step is to take an earthenware vessel, which resembles an ordinary stone crock, and first pour into it a small quantity of acetic acid, which is about the same as table vinegar. Then the crock or pot is filled up with the lead buckles.

Where this white lead is made in a large way many thousands of these pots are placed in a building, the sides of which are walled up tight, the spaces between the crocks being filled in with tan bark. After the floor has been covered with a layer of these crocks, the layer is covered with boards, in order to provide a foundation for setting in the next layer of crocks and tan bark. The layer of boards also serves as a floor to keep the tan bark from falling into the open crocks on the tier below. This procedure is followed with tier after tier until the building is completely filled.

Corrosion of the metallic lead in the pots now begins, because the tan bark generates some heat, becoming finally quite warm. This heat causes the acetic acid or vinegar to throw off vapor or steam, which attacks the metallic lead, causing it to decompose or corrode. This process goes on for many weeks (sometimes as much as fifteen or sixteen weeks), until those buckles of metallic lead have become a mass of white powder and nearly all trace of the original metallic lead has disappeared.]

[Illustration: A LEAD BUCKLE AFTER CORROSION.]

[Illustration: A LEAD BUCKLE BEFORE CORROSION.]

[Illustration: HOW OXIDE OF ZINC IS OBTAINED

WASHING THE LEAD. SCREENS COVERED WITH CLOTH REMOVE ALL FOREIGN MATTER.

After these many weeks have passed, the pots containing the white powder of carbonate of lead, as it is called, is taken out of the building where corrosion took place, and the white deposit is put through an elaborate system of refining, which is called “washing,” and, in fact, is really washed in water, and is then dried in very large copper pans. After being dried it is in the form of large white cakes, resembling pieces of chalk. These cakes are then passed through a mill, which grinds them to very fine powder, which is packed in barrels ready to be shipped and used by the paint-maker.]

[Illustration: FURNACE WHERE THE SULPHUR IS ROASTED OUT OF THE ORE.

Now that we have followed through the process of making the white-lead powder, or pigment, let us take a little time to study the preparation of the other white powder, known to the paint trade as “oxide of zinc.” This is prepared in a manner quite different from that of the white lead.

First the ore which is mined from the earth containing the metallic zinc is carefully selected by expert workmen and placed in a special kind of furnace, being mixed with hard coal, such as we use in our heating stoves.]

[Illustration: A ZINC SMELTER--THE MEN KEEP THEIR MOUTHS COVERED SO AS NOT TO INHALE THE VAPOR, WHICH IS POISONOUS

The burning of the coal causes an intensely high temperature, sometimes being several thousand degrees. This causes the zinc ore to be consumed as it were or to pass into a form of vapor. This vapor is carried through huge pipes which are several feet in diameter and extend for a long distance. While these vapors are passing through these pipes it becomes cooled. After becoming cooled it takes on the form of very fine white powder, coming from the pipes in much the same way that snow falls from the sky in the winter. This is collected and placed in barrels, after which it is ready for the paint-maker without further preparation.]

~WHERE LINSEED OIL COMES FROM~

Since we have followed the preparation of the two important white pigments used in making our can of paint, it is now important that we devote a little thought to the liquid which is to be used. This is called “Linseed Oil.” Linseed oil is of a golden yellow color, resembling the appearance of thin syrup which we sometimes have on the table. This oil is taken from the seed of the flax plant. It might better be called “Flaxseed Oil,” yet it is not commonly known by that name, but is nearly always referred to as “Linseed Oil.” Flax is grown in many parts of the world, the most important places being the United States of America, Dominion of Canada, Ireland, India and the Argentine Republic. In the United States, the seed is sown early in spring, much the same as is done with other crops, and ripens and is harvested early in the fall of the year. The harvesting and separation of the seed from the plant or straw is done very much in the same way that other crops, such as wheat and oats, are harvested. The seed is then taken to market and is ready for the extraction of the oil, which is done by men who are known as “oil crushers.”

[Illustration: PRESSING OIL OUT OF FLAXSEED.]

[Illustration: REMOVING OIL CAKE FROM PRESS.]

The oil is extracted from the seed by a very simple process. Usually the seeds are heated by steaming them, after which they pass through a mill, being ground to a coarse mass, which is then placed in very powerful machines called “Hydraulic Oil Presses,” which squeeze the oil from the seed, leaving the remainder in the form of large cakes which are then ground to a mealy-like powder which is used as food for cattle and is very much prized.

The oil which has been extracted by this process is put into large tanks where it is clarified and is then ready for the paint-maker. This oil is often referred to as “Vegetable Oil” and it has one very peculiar and very important characteristic which makes it useful and necessary for use in paint. This property is that of drying or becoming solid, losing all tendency to stickiness after it has been spread out thinly and exposed to the air for a short time.

[Illustration: WHERE LEAD IS GROUND IN OIL.]

[Illustration: WHERE PAINTS ARE MIXED.]

Now that we have given attention to the preparation of the most important things used in the making of our can of paint, let us look a little to the manner in which they are put together, and the result.

The oil is necessary in making paint in order to make it fluid, so that the paint may be brushed on to the wood or other surface, and also so that the pigment or powdered material which has been put into the paint will have something to hold it to the surface. The oil or other liquid which may be used is usually called “Binder” by the paint man because it binds the pigment in the paint and to the surface on which it has been spread or applied.

In a large paint factory, the two white pigments, lead and zinc, are mixed with linseed oil in large machines known as “Mixers” into a smooth paste which is then run through other machines called “Mills,” where the paste is ground very fine into large tubes where the paint is finished by mixing in enough more oil to make it of the proper thickness or consistency for brushing. In this state it can be used, but would not be entirely satisfactory because it would dry very slowly. For that reason, the paint-maker adds in a small amount of what is known as “Drier,” which causes the paint to dry much more rapidly after it is spread out on any surface.

The paint-maker may also add in a small amount of thin liquid called “Turpentine,” which also aids in the drying and the working of the paint. Turpentine is a very thin liquid which looks like water, and it is derived from the sap of one species of pine which grows abundantly in the southern portion of the United States. The sap is taken from the tree by tapping the tree or making an incision called a box, at certain seasons. After the sap is collected it is put through a heating process called “distilling,” which separates the water-white liquid, called turpentine, leaving a large mass of heavy material which is commonly known as “Rosin.” This turpentine is very useful to the paint-maker and the painter. It is also used for many other purposes.

~WHAT MAKES THE DIFFERENT COLORS OF PAINT~

The paint which we have described is the most simple kind and is white. There are many other kinds of paint used, being of many different colors. All of these different kinds require different treatment and preparation and would require many large books to explain even in a brief way.

The white paint which we have described may be colored or tinted to many different hues by adding suitable color pigments. These color pigments are of many kinds and are derived from many different sources. The vegetable kingdom is represented as well as the mineral and animal kingdoms. The linseed oil which we have already mentioned, is derived from the vegetable kingdom. This also applies to some few of the pigments. A very important instance which we might mention is a beautiful rich brown called “Vandyke Brown.” This is made from decayed vegetation which is found in swampy districts. There are many pigments derived from the mineral kingdom. White lead and zinc oxide have already been described as useful. Among colored pigments coming from this kingdom, we might mention yellow ochre, sienna, umber, cobalt blue, and many others.

The animal kingdom supplies quite a number, one of which is a beautiful red known as “Carmine.” This is taken from a small insect or fly which is found in certain tropical climates. The production of carmine is very expensive and the product is highly prized.

Another important development of the animal world is what is called “Bone Black.” This is made by taking ordinary animal bones, putting them into a suitable furnace and burning them, which really produces bone charcoal, which is refined by powdering and washing, and finally produces a beautiful black, such as used for painting fine coaches and carriages.

Why Does a Dog Turn Round and Round Before He Lies Down?

Away back in the history of the animal kingdom, when the ancestors of our domestic dog were wild, they slept in the woods or open. When they were ready to lie down, they first had to trample the grass about them flat to make a place to lie down. This became a habit and one of the instincts of the animal which has been transmitted to the dogs of today who keep it up. It is an inherited habit quite useless to the dogs of to-day.

How Is Light Produced?

You already learned that a substance called ether is found in all substances, filling the spaces between the molecules. When the molecules are made to vibrate, the ether naturally also vibrates. As soon as the vibrations become sufficiently rapid, they produce the sensation of light. These vibrations also produce heat. In heated bodies the molecules are always found to be in vibration, and a body may become so hot that it gives off light. We notice this when iron becomes red hot. Heat and light are found together in bodies in many instances. In fact, most of the light we have comes from bodies which are hot. The sun is so hot, that it is surrounded by the gases of many substances that exist as solids on earth.

We have some bodies which produce light which is not accompanied by much heat. The glow-worm, or firefly, seems to make light with little or no heat; but we do not yet know how this is done. Almost all sources of artificial light require that heat be produced before light obtained. Only such vibrations of the ether which are sufficiently rapid produce enough light to enable us to see. For this reason, a piece of red hot iron, which is made luminous by heat and whose

## particles vibrate less rapidly produce little light.

What Makes Rays of Light?

Whenever the ether is made to vibrate rapidly enough at any point, the vibrations go in straight lines from the source of light in all directions. A single line of vibrating particles in the ether, is known as a ray. A number of rays, that issue from one point, are said to form a pencil. A pencil of light may be produced by holding near a candle a screen, with a hole in it. Sometimes rays of light are brought together in a point, as may be done by means of a burning glass, and one of these bundles of rays is known as a convergent pencil.

A bundle of rays that lie parallel to each other forms a beam. The rays that come to us from the sun are practically parallel and are called sunbeams.

Why Does a Nail Get Hot When I Hammer It?

When we are in the sunshine, or standing before a fire, we feel hot; when we take snow or ice in our hands, they feel cold. The thing which produces these sensations is called heat. When we feel heat, it is because heat is absorbed by our bodies, and when we feel cold, it is being thrown off by them.

To answer this question, we must see how heat may be produced. If we draw a cord rapidly through our fingers, they feel hot, and if we rub a coin briskly with a cloth or our hands, it becomes warm; if we take a nail and hammer it on a hard substance, it becomes too warm for us to hold. In these instances heat is produced by retarding or checking the motion of a body. When we draw a cord through our fingers, it moves less easily; we retard its motion by gripping it and this is what makes the heat we feel. When we strike the nail with a hammer, the motion of the hammer is checked by the nail, and the faster we pound with the hammer, the hotter the nail becomes. From these experiments we learn that whenever the motion of a substance is checked, or retarded, heat is generated, and the substance made hot.

In explaining this method of producing heat, it was at one time thought that all bodies contained a substance which produced the heat and that, when rubbed or hammered, this substance was thrown off. About the end of the 18th century, however, it was shown by Benjamin Thompson (Count Rumford), that substances when rubbed give off heat. From this we learned that heat is not a substance, because the quantity of any substance, present in a body, cannot be limitless. If it were a substance which produced the heat, the supply would sooner or later be exhausted, and rubbing could no longer produce heat.

Heat produced by rubbing, or by striking substances together, is caused as follows: If two substances are struck upon each other, the whole of those substances are checked, but the molecules of the substances are made to vibrate very rapidly, and these vibrations produce the heat we feel.

How Do We Obtain Heat?

We get most of our heat from the sun. If the heat from the sun did not reach us, no living thing would exist on the earth. No plants or animals could live; the oceans and rivers would be solid ice.

Another important source of heat, is chemical action. Chemical action is what causes fire. Even when it does not cause fire, it produces a great deal of heat. When we breathe to keep our bodies warm, it is a chemical action that occurs. Fire is the most important form of chemical action, as a source of heat.

Why Does a Glow-Worm Glow?

A glow-worm is a kind of beetle which may be found in the yards and hedges in the summer time. The name applies only to the female of the species which is wingless and whose body resembles that of a caterpillar somewhat and emits a shining green light from the end of the abdomen. The male of this species has wings but does not show any light as does the female and resembles an ordinary beetle. The male flies about in the evenings looking for the female and she makes her light glow in order that the male may find her. Glow-worms are found mostly in England. There are, however, some members of the same species of beetle common to the United States. We speak of them as fireflies or lightning bugs. The female of these also is the only one carrying a light, although unlike the glow-worm she has wings and can fly.

Why Do They Call It Pin Money?

This expression originally came from the allowance which a husband gave his wife to purchase pins. At one time pins were dreadfully expensive so that only wealthy people could afford them and they were saved so carefully that in those days you could not have looked along the pavement and found a pin which you happened to be in need of as you can and often do today.

By a curious law the manufacturers of pins were only allowed to sell them on January 1st and 2nd each year and so when those days came around the women whose husbands could afford it, secured pin money from them and went out and got their pins.