Part 49

When a string is plucked in the middle, it vibrates as a whole, and its rate of vibration, or vibration frequency, is determined by the three conditions that have just been discussed; but if a finger is laid on the string, in the middle, and the string is plucked between the middle and the end, the string will vibrate in halves, and the middle point will remain at rest. If the string had been touched at a point one-fourth of the length from the end it would have vibrated in fourths, and there would have been three stationary points.

When vibrations are set up in a string, with nothing to prevent the free vibration of the whole string, it first vibrates as a whole, and the sound produced is known as the fundamental tone of the string; but very soon smaller vibrations of segments of the string begin, first of halves of the string, then of thirds, and then of fourths. These smaller vibrations produce sound waves that blend with the fundamental tone and are known as overtones. The combined sound of the fundamental tone and the overtones is called a note. The overtones present in notes that have the same fundamental tone are not the same when the notes are produced by different instruments, and, consequently, the sound of notes of the same pitch is not the same on different instruments. This difference in notes of the same pitch has already been mentioned, but the way in which overtones are produced was not explained in connection with it.

In wind instruments the sounds are produced by the vibrations of columns of air in pipes. In the organ, which is probably the best example of a wind instrument, the vibrations are usually produced by causing a current of air to strike a sharp edge, just above the opening of the pipe, as is done in a common whistle. A portion of the air current is deflected into the organ pipe, and it sets up vibrations in the air within the pipe.

The pitch of the sound produced by an organ pipe is determined by the length of the pipe. A pipe that is open at both ends, called an open pipe, produces a sound that has a wave length twice as great as the length of the pipe; and if the pipe is open at one end only, a closed pipe, the sound produced has a wave length twice the length of the open pipe. Hence it will be seen that a closed pipe produces a sound that has the same pitch as that produced by an open pipe that is twice as long.

Talking Machines.

The phonograph, graphophone, gramophone, sonophone, and other talking machines, furnish one of the best proofs of the wave theory of sound, because their invention was based upon that theory. The first talking machine was that invented by Thomas A. Edison and called by him the phonograph. The others merely show the principle of the phonograph applied in different ways, and need not be separately described. The reasoning that led Edison to invent the phonograph was that if the sound waves produced by the human voice were allowed to strike a thick disk of hard rubber or metal, they would cause the disk to vibrate in a certain way, and if the disk were again made to vibrate as it had done under the influence of the voice, the sounds of the voice would be reproduced. The difficult part of the task of making a talking machine was in finding a way to make the disk vibrate again as it did under the influence of the voice. This, however, was finally accomplished, providing the disk with a needle, that rests on a cylinder of hard wax, which turns slowly under the point of the needle while the sound waves are striking the disk. The vibrations of the disk cause the point to indent the surface of the wax so as to produce a groove of varying depth on its surface. After the vibrations of the speaker’s voice have been recorded in this way on the surface of the wax cylinder the needle can be made to retrace its path, and will cause the disk to vibrate as it did under the tones of the speaker’s voice. These last vibrations of the disk produce sound waves similar to those of the voice, but their amplitude is less and the sound is not so loud.

Why Does Red Make a Bull Angry?

It is very doubtful if a red flag really makes a bull more excited or more quickly than a rag of any other color or any other object which the bull can see plainly but does not understand. Conceding for the moment that red excites a bull more than any other color, the answer to the question will be found in the statement that anything unusual which the bull sees has a tendency to make him angry and the thing which he can see at a distance more quickly will start him going most quickly. He can see a red rag better perhaps than almost any other color. There may be something about the color which excites him just as some notes on the piano will worry some dogs, but there is no way of studying the bull’s anatomy to determine why red should excite him more than any other color, if that is so.

HOW A KEY TURNS A LOCK

What Happens When the Knob is Turned?

All of that portion of the lock which is shown above the round central post is operated by the knob, the spindle of which passes through the square hole. Before the knob is turned, the parts are in the position shown in figure 2, with the latch bolt protruding. Turning the knob to the left gives the position shown in figure 1, the upper lever in the hub pushing back the yoke, which in turn pushes back the latch bolt. When the hand is removed, the springs cause the parts to return to the position shown in figure 2. Turning the knob to the right also retracts the latch bolt, as shown in figure 3, by means of the lower lever on the hub.

The spiral spring on the latch bolt is lighter than the one above it. This gives an easy, lively action to the bolt, with very little friction when the door is closed, while the heavier spring above gives a quick and positive action of the knobs.

What Happens When the Key is Turned?

All of that portion of the lock which is shown below the round central post is operated by the key. The square stud is attached to the bolt, and in figure 1, it is seen that the projections on the flat tumblers prevent the stud from moving forward, holding the bolt in retracted position. When the key is turned as shown in figure 2, it raises the tumblers releasing the stud, and then pushes the bolt out, the tumblers falling into position as shown in figure 3, with the projections again engaging the stud and preventing the bolt from moving until the key is turned backward, again raising the tumblers and releasing and retracting the bolt.

How Key Changes Are Provided.

There are three ways in which keys are made individual to the locks they fit.

_a._ By changing the shape of the keyhole. This may be done shorter or longer, wide or narrow, straight or tapering and with projections on the sides which the key must fit, making it difficult or impossible for keys of a different class to enter the lock. In the lock shown, a projection on the keyhole will be noted, fitting a groove in the bit of the key.

_b._ By wards attached to the lock-case. The two crescent-shaped wards seen near the key in figure 2 illustrate this feature. Similar wards are placed on the lock cover. These fit into the two notches shown on the key bit in figure 4, and their shape and position are varied at will.

_c._ By changes in the tumblers. There are five flat tumblers in the lock shown, and their lower edges fit into the end of the key bit. By varying their height, changes in the cutting of the key are made necessary.

The security of a lock depends very largely upon its being so made that no key will operate it except the one which belongs to it, and this is obtained by guarding the keyhole by means of _a_, by preventing the wrong key from turning by means of _b_, and by still further limitations by means of _c_.

The Cylinder Lock.

Door locks of the highest grade of security are made with a locking cylinder, which contains tumblers in the form of miniature bolts which make it impossible to operate the lock except with the key to which it is fitted. This is screwed into the lock-case through the side of the door, with the lever on the inner end engaging the end of the bolt in the lock, so that as it is moved it either retracts or “throws” the bolt as desired.

Figure 1 shows all the parts of a modern master-keyed lock. Figure 4 shows a broken view of the cylinder with all parts in position. Figure 3 shows a simpler form used when the master key is not desired. Figure 2 shows the front, the only part which is visible when the lock is in use, with its keyway of tortuous shape which will not admit flat-picking tools.

When the lock is assembled, the pin tumblers project through the shell, the master cylinder and the key plug holding all parts firmly bolted or fastened together. When the proper key is inserted, the tumblers are raised until the “breaks” in all of them coincide with the surface of the key plug, releasing it and permitting the key to turn it. If any one of the five tumblers is .002 inch too high or too low, the key will not turn; so that no key except the one made for the lock can be used.

In the master-keyed lock, the master key causes the breaks to coincide with the outer surface of the master ring. It is thus possible to have a master key which will fit any desired number of locks with the individual or change keys all different from each other and from the master key.

The balls reduce friction to such an extent that a key has been inserted and withdrawn for a million times without affecting the accuracy of the lock.

Where Does Salt Come From?

Salt is one of the things with which we come in contact with daily perhaps more than any other. With the exception of water, probably no one thing is used more by all civilized people than salt.

You have already learned in our talk on elements the difference between a mere mixture of substances and a chemical compound. You remember that when some substances are only mixed together, they do not lose their identity. In a compound the substances are always combined in fixed proportions and the properties of the compound are often very different from those of the things that make it. Common salt is made of two substances, that are not at all like salt, and are very different from each other. One, sodium, is a soft, bluish metal, and the other is chlorine, a yellowish-green gas. The chemical name for salt is sodium chloride which is derived from the two names sodium and chlorine.

Sodium and chlorine are both what we have learned to call elements. An element being a substance which cannot be separated into substances of different kinds. There are now known about seventy such elements. All the substances around us are composed of these elements alone, or chemically united in different compounds, or simply mixed together. Most of them, however, are mixtures, not of separate elements, but of compounds. The soil under our feet is a mixture of compounds. Water is also a compound. Pure compounds very rarely occur naturally. Salt is sometimes found almost pure; but generally is mixed with so many other things that we have to take them out to get absolutely pure salt. For practical every-day use it is unnecessary to purify the salt.

Salt is found in large quantities in the sea water, in which it is dissolved with some other substances. It is also found in salt beds, formed by the drying up of old lakes that have no outlets; salt wells, that yield strong brine; and salt mines, in which it is found in hard, solid, transparent crystals, called rock salt. Rock salt is the purest form in which salt is found and, to prepare it for market, it is merely necessary to grind it or cut into blocks. The greatest deposit of salt in the world is probably that at Wielizka in Poland, where there is a bed 500 miles long, 20 miles wide, and 1,200 feet thick. Some of the mines there are so extensive that it is said some of the miners spend all their lives in them, never coming to the surface of the earth.

A trip through these mines is interesting. In one of them can be seen a church made entirely of salt. The salt supply of the United States is obtained chiefly from the salt wells of Michigan and New York, the Great Salt Lake in Utah, and the rock-salt mines of Louisiana and Kansas.

In the arts and manufactures, the most important uses of salt are in glazing earthenware, in extracting metals from their ores, in preserving meats and hides, in fertilizing arid soil, and also, as we shall presently see, in the manufacture of soda. Of equal importance, perhaps, is its use in food. Most people think it not only lends a pleasant flavor, but is itself an important article of diet. It is certain, that all people who can obtain it use salt in their food, and where it is scarce, it is considered one of the greatest of luxuries.

Soda is of interest to us, not so much on account of its use in our households, as because it plays on extremely important part in two industries that contribute greatly to our comfort, viz., the manufacture of glass and soap.

Soda is not found naturally in great abundance, as salt is, but is generally made from other substances. Formerly it was made almost entirely from the ashes of certain plants. One, known as the Salsoda soda-plant, was formerly cultivated in Spain for the soda contained in it, and the ashes, or Barilla, as they were called, were soaked in water to dissolve out the soda. Now, however, the world’s soda supply is produced from common salt by two processes, known from the names of their inventors as the Leblanc and Solvay processes.

~WHERE WE GET SODA~

In the Leblanc process the first step is to treat the salt, or sodium chloride, with sulphuric acid. As a result of this, a compound of sodium, sulphur, and oxygen, called sodium sulphate is formed, together with another acid containing hydrogen and chlorine, and called hydrochloric acid. This acid is driven off by boiling, and the sodium sulphate is left.

The next step in the process is to convert the sodium sulphate, or “salt cake,” into soda, or, to give it its chemical name, sodium carbonate. This change is brought about by mixing the salt cake with limestone and coal and heating the mixture. Just what changes go on when this is done, are not known, but the chief ones are probably the following: the coal, which consists for the most part of an element called carbon, takes the oxygen out of the sodium sulphate, and unites with it to form carbonic acid gas, leaving a compound of sodium and sulphur called sodium sulphide; this acts on the limestone, which is composed of a metal, calcium, in combination with carbon and oxygen, and causes the sulphur in the sodium sulphide to combine with the calcium, forming calcium sulphide, while the sodium combines with the carbon and oxygen and forms the desired compound, sodium carbonate. After the heating, the resulting mass which contains calcium sulphide, sodium carbonate, and some unburned coal, and is known as “black ash,” is broken up and treated with water. This dissolves the sodium carbonate, leaving the rest undissolved, and when part of the water is evaporated crystals containing sodium carbonate and water are formed. By heating these the water may be driven off, and the sodium carbonate left behind as a white powder.

The Solvay, or ammonia soda, process consists in forcing carbonic acid gas through strong brine, to which a considerable quantity of ammonia has been added. When this is done, crystals are formed in the brine, which are composed of a compound of hydrogen, sodium, carbon, and oxygen, and are called sodium bicarbonate. This substance, which is the soda we sometimes use in baking bread, is decomposed by heating, into water and sodium carbonate, the soda used for washing.

The Leblanc process was formerly used almost altogether for making soda; but in recent years the Solvay process has come into extensive use, and it is said that now more than half the soda of the world is made in this way.

Where Do All the Little Round Stones Come From?

The little round stones you are thinking of are really pebbles which have been worn smooth and round by being rubbed against each other in the water, through the action of the waves on a beach, or the running water of brooks and streams. This sort of rock is called a water-formed rock. Some of them have travelled many miles before they are found side by side on the shore or in a large mass of what we would call conglomerate rock. But whenever you see a round smooth rock or pebble you may be quite sure that it was made round and smooth by the action of water.

You sometimes see large rocks made of small stones of various colors and sizes. You can often find a large rock of this kind standing by itself. If you examine it carefully, you will find it consists of an immense number of small stones of different sizes and of a variety of colors, all fastened together as though with cement. This kind of rock is called conglomerate. We know two kinds of conglomerate rock, one, quite common, in which the little stones are round and smooth, and another, not seen so often, in which the stones are sharp. The latter sort is sometimes called breccia, to distinguish it from the former, which is called true pudding stone.

What Is Clay?

Clay is the result of the crumbling of a certain kind of rocks called feldspars. When feldspar is exposed to the action of the weather, it crumbles slowly at the surface and the little fragments combine with a certain amount of water, forming clay. Pure clay is white and is used in the manufacture of china and porcelain. The common clay that we usually think of when we think of clay, is generally yellowish, but there are many different colored clays. Most of these colors, particularly those of red clay, yellow clay and blue clay, come from the iron which is present in the clay. Clay which contains iron is useful for making bricks. Bricks are made from clay by first softening the clay and pressing it in molds, the size of a brick. When dried for a time in the sun they are put into an oven and baked in great heat and they become quite hard and generally red. Most of the clay from which bricks are made turns red when baked, whether blue, yellow or red, because the iron which is in the clay is generally turned red when subjected to heat.

For making porcelains it is desirable to use the kinds of clay which contain nothing that melts when heated to a high degree. Clays which contain substances which melt in strong heat are, therefore, not good for making porcelains. There is a pure white clay called Kaolin which is very excellent for this purpose. Clay out of which we make firebrick for lining stoves and fireplaces is free from substances which melt. Several kinds of clay are good for making paints.

Where Do School Slates Come From?

Slates such as are used in school and as roofing material are formed of clay, which has been hardened under pressure and heat. When this occurs it does so because a number of layers of clay, one on top of the other, have at sometime been subjected to great heat and pressure within the earth with the result that the clay is pressed into very thick layers and changed in color by the heat and becomes hard. There are many kinds of slate. Some of the slate, as found in slate mines, is used to make roofs over buildings and for this purpose they are cut to shapes very much like wooden shingles. They are easily broken, however, as slate is very brittle.

Slate is used in many other ways besides for roofs and school slates. Sometimes it is made into slate pencils but, since paper has become so cheap, comparatively few slate pencils are used in the school room today.

What Causes Shadows?

Where anything through which rays of light cannot pass intercepts the light rays coming from a luminous body, the light rays are turned back in the direction from which they come and the part on the other side of the object which intercepted the light goes into shade and a shadow results. A shadow then is produced by cutting off one or more light rays. We notice shadows when the sun is bright in the daytime and at night when we walk along the streets lighted partly by street lamps. The shadows we see in the daytime are caused by our cutting off and throwing back some of the light rays which come from the sun. These are not so dark as the shadows we see at night because the rays of light from the sun are so bright and are reflected from so many other objects to the side and in back of us.

When, however, we are walking along a dimly lighted street and come to a street lamp the shadows our bodies cause are quite black. The night shadows are darker because the source of light is less intense and the objects to the side of and in back of us (if we are walking toward the light) do not reflect so much of the light rays as they do of the sun’s rays in the daytime.

The Foundation of a Sky Scraper

How Hollow Steel Piles, Compressed and Concrete Are Employed to Make a Foundation

Rapidity of building construction is of primary importance in every city of metropolitan size. When real estate is sold at the rate of several hundred dollars a square foot it is self-evident that time is indeed money. The delay of a few days in completing a structure may deprive the owner of the chance of earning thousands in rental money. Because of the excessive depth of an open caisson, the completion of a foundation may be delayed for months. Hence the building may not be completed until the renting period has passed and the owner must wait an entire year before he can expect any financial return on his investment.

Because rapidity is so essential in city building construction the method of first sinking an open pit to rock in providing a foundation has been displaced to a large extent by a system in which heavy hollow steel piles are employed in clusters to support a building. The hollow piles are driven through quicksand to rock, cleaned out and ultimately filled with concrete.

~PILES ARE DRIVEN DOWN TO SOLID ROCK~

In this method of constructing foundations, which is illustrated, hollow steel piles are driven in the well-known manner down to solid rock. The steel pile sections vary in length from 20 feet to 22 feet, and in diameter from 12 inches to 24 inches. If the ground is to be penetrated to a depth greater than 22 feet, the sections of piling are connected by means of a sleeve in such manner that a watertight joint is formed. Under a pressure of 150 pounds to the square inch a jet of compressed air is then employed to blow out the earth and water contained within the shell. A spouting geyser of mud rising sometimes to a height of 150 feet, and occasional large pieces of rock blown up from a depth of 40 feet below the ground, bear testimony to the terrific force of the air blast.