Part 23

It is significant that the "dry" battery cell must be moist in order that chemical action may go on in it. Compare with that fact several others that we may learn from observation, for example: Baking powders must be kept dry to retain their strength. That is, if they get moist chemical action will begin in them, and the gas which is one of the products of this chemical action will pass off. Now it is the sole function of baking powders to produce gas within the dough, and if the gas has wholly or partially escaped they will fail to make the bread stuff "light." The same reasons obtain for keeping seidlitz powders and other effervescing salts, such as vichy and kissingen, dry. It is to prevent the chemical action which is provoked by the presence of water. The same thing is true of the rusting of iron, and the various kinds of corrosion of metals. We may prevent such action indefinitely by keeping them dry. Berries, fruits, meats, milk, eggs, grain--all kinds of foods--are preserved from spoiling--from chemical changes--by drying them and keeping them dry. The same thing is true of wood, paper, cloth, etc. A wooden fence post may last from five to ten years. A fence rail, being less exposed to moisture, may last two or three times as long. The interior wood of a house may last a century or two, while the exterior wood, being exposed to the weather, may require repairs very frequently. Shingles on the roof do not last as long as shingles on the side of the house. Those on a steep roof last longer than those on a flatter one. A pitch of at least forty-five degrees in a roof is desirable to keep it dry. The north and west sides of a house being least exposed to storm in this climate last the longer. Precious books, records, deeds, wills, etc., on paper must be preserved in dry air. A sail will keep strong and white if kept dry.

But it is impressed upon us by our experiences that sunlight is even more potent than moisture to produce chemical change. Photographic processes are dependent upon the power of light to produce chemical changes. The fading of our tapestries and our garments, the tanning of our skins, the development of green material in the leaves of plants, all are evidently the direct result of sunlight. A picture hung on the wall prevents the wall paper behind it from being faded by the light, or it prevents the wood behind it from being turned yellow by the light. Folds in our garments prevent them from being faded all alike. Very many substances to be found in a chemical laboratory, in a drug store, or in a kitchen must be kept in the dark if they are to be guarded against chemical change. No experienced housewife would let a barrel of flour or potatoes sit in the sun, and every housewife knows that the sun is the best agent for bringing about those chemical changes which she desires. Hence she puts her bedding, her milk pans, her bread box, her butter jar, etc., "out to sun." She has open plumbing, that the sun may enter those dark and dirty corners.

If you would guard a substance against chemical change, keep it in a dry, dark place. We have come to associate the sun and the weather as disintegrating forces. Hence the south and east sides of the building need most frequent repairs. Every one who has made time exposures in photography knows that the sunlight from the east is, as a rule, two or three times as powerful as that from the west. There is less moisture and dust in the air to screen us from the early morning sun than from the late afternoon sun. When there is enough moisture in the air to make the sun look red, those rays from it which would produce chemical action, called actinic rays, are cut off. Photographic processes are then exceedingly slow. It is like exposing a plate in a dark room behind the ruby glass.

But our daily experiences teach us that not only moisture and light but also heat stimulates chemical action. We restrain chemical action by cold when we put things in the ice box. We hasten chemical action by heat when we put things on the stove. Winter restrains all the chemical activities of nature, and summer quickens all the vegetable and mineral kingdoms into chemical activity. If we would preserve a substance from chemical change we must keep it in a cool, dark, dry place. Now those conditions which will favour the chemical activity of a battery cell will enable it to produce electricity, and those conditions which will restrain chemical action will enable us to preserve the cell from running down.

But we have lately learned that other forms of radiation besides light and heat exist and aid in chemical action. We may produce radiographs--pictures on photographic plates--without light but with invisible rays, which are akin to light and to electricity.

XVI

ELECTROCUTION AT MILLVILLE

The old mill was infested with rats. My wife laid down to the boys the principle that good housekeepers were never troubled with vermin of any kind. The rats' sole occupation is to search for food. If you don't feed them they will not stay with you. But the boys said that they were glad of a chance to try an experiment on the rats. So one day when I went down to the mill I found them discussing the possibility of killing the rats by electricity. Harold said that he had read that it took much less electricity to kill any animal than to kill a man, and he would like to try, for instance, whether the shock which they had received from a bell would kill a rat.

"Well, who's going to sit by," said Erg, "to close the primary circuit when the rat happens to get himself into the secondary circuit?"

"Make him close it himself by some device," said Ernest.

"They have a regular thoroughfare, a beaten highway, along by the wall, under the mill and up through a hole in the floor of my bedroom," said Dyne.

"Well," said Harold, "I propose an electric trap which shall have two compartments. We will keep cheese in the inner compartment, the walls of which shall be of wires so that the rats may see the cheese. The floor of the outer apartment shall be covered with wire, as shown in Fig. 154. The wires of the secondary circuit from the bell (Fig. 156) shall be fastened to the binding posts b and c (Fig. 154). The partition d shall be a swing door into the apartment A where the cheese is. This is shown in profile in Fig. 155. d must act as a switch to close the primary circuit through the bell P (Fig. 156). We will have three dry cells in the primary circuit. Now this is the way it will work: A rat comes up from under the mill with wet and slimy feet--just suited for making contact for the electric current to enter his body. The smell of the cheese attracts him. He circles around the trap several times, watching the cheese in apartment A through the wire screen. He sees a narrow opening into this apartment under the door d. He puts himself in position upon the floor of the outer apartment B, his feet bridging the gaps between the two systems of wires belonging to the secondary circuit. When he thrusts his head under the door and pushes it, it swings in a little, bringing one metal strip against another, which belongs to the primary circuit. This closes that circuit. He will never hear the bell ring, for the electric current which will shock him to death travels 186,000 miles per second, while his sensations travel only sixty miles an hour. If the involuntary recoil of his muscles does not make him jump back, so that the door will shut and stop the bell from ringing, Dyne will be awakened and he will close the door, since we will put the trap at that hole where the rats enter his bedroom."

The next night three rats were electrocuted by this device.

I told the boys they had so many interesting things going on at the mill that we should have to have a telephone between it and the cottage so that we could talk them over.

XVII

THE TELEPHONE

The telephone was the great invention of our centennial year, 1876. Elisha Gray and Alexander Graham Bell each claimed to have been the inventor. It is quite probable that each did discover it independently, but the result of the long patent suit was that the court awarded the claim to Bell. It is, therefore, known as the Bell telephone.

Many who installed telephones during the first few years of their existence had them taken out again as nuisances. They are far greater nuisances now than at that time, but the necessity of them has come upon us and entirely enslaved us.

There were more than eleven billion messages sent by telephone in the United States in 1907. The capital invested in telephone business was $814,616,004. The income for that year was $184,461,747. All of these items had more than doubled during the previous five years. In 1880 there were about eight times as many miles of telegraph wires as of telephone wires. In 1907, there were about eight times as many miles of telephone wires as of telegraph wires. The Bell system had 3,132,063 stations, and independent companies had 2,986,515 stations in 1907.

The first telephone line ran from Salem to Boston, Mass. This was in 1877. The next year the first telephone exchange was established. It was eight years before a telephone line was extended from Boston to New York. On October 18, 1892, the first telephone message was sent from New York to Chicago. Previous to 1895 telephoning, like telegraphing, was done by one wire, using the earth, as we say, to complete the circuit.

But at about that time electric car and electric lighting lines became so common that they interfered with telephoning. These currents running in lines parallel to the telephone wires induced currents in them, and when a person put a receiver to his ear for conversation he heard the hum of electric light dynamos and the buzz of electric cars so loud that conversation was quite impossible. The next step was to introduce a return wire--the double metallic circuit as we call it. Thus outside currents induce equal and opposite currents in the two wires of the circuit, which neutralize each other.

It was this same year, 1895, that the "central battery" system was introduced into telephone equipment. This is not usually a battery at all, but a dynamo.

The price of all electrical supplies in 1895 was about one tenth what it had been in 1885, and at the same time the goods were of far better quality.

Important telephone patents expired in this year, and immediately private and independent lines began to be established. It was also in 1895 that the telephone company began to use an automatic registering device which enabled it to charge telephone rates according to the number of calls.

The boys unscrewed the end of a telephone receiver (Fig. 157) and found inside a permanent magnet made of several steel bars bolted together (Fig. 158). This was shown to be a magnet by presenting a small pocket compass to either end. The left-hand end of this magnet proved to be its north pole by repelling the blue end of the compass needle.

On the left-hand end of the magnet was a small spool of No. 36 copper wire, silk covered. It offered 75 ohms of resistance, and since it takes 2-1/2 feet of this wire to furnish 1 ohm of resistance the spool contains 187-1/2 feet. A thin disc of soft iron .01 inch in thickness is held by the hard rubber case very near to but not quite touching this end of the magnet. We drew this disc to one side, as shown in Fig. 159, and connected the receiver by wires to a magneto. We turned the crank of the magneto slowly and the iron disk danced up and down, keeping time with the revolutions of the armature. The magneto furnished an alternating current, which, when it flowed around the coil in one direction, strengthened the pole of the magnet, and in the reverse direction weakened the pole. When the crank was turned so as to produce twenty to thirty revolutions of the armature per second the dancing of the disc sounded like the low hum produced by the wing of a humming bird. When a large, wide-mouthed bottle was brought near to this the sound was greatly reinforced, as the sound of a bee becomes louder when he appears at your open window. We next replaced the iron disc and put on the cap again. We then connected the receiver at S (Fig. 160) and connected two dry cells at p. When the primary circuit was closed the disc vibrated in time with the hammer of the bell making the same tone. We substituted for the bell a series of buzzers. The smallest had an armature about one inch long, while that of the largest was about two inches long. The shorter the armature the faster it vibrated, and the higher was the pitch of its tone. We arranged these as shown in Fig. 161. A, C, D, E and F are the buzzers. B is a battery of two cells and G, H, I, J and K are springs of sheet brass which act as push buttons. By operating upon these springs with one's fingers, as upon the keys of an organ, it was possible to represent the tones of a reed organ after a fashion. The armatures are reeds and they are made to vibrate by electro-magnets. We called it an electric organ. The telephone receiver was connected at T, and the wires which led to it were lengthened so that the receiver might be a long distance away. The disc in the receiver kept time with the armature of each buzzer when it sounded and faithfully reproduced its sound. But the strangest thing was that when any two buzzers sounded together, or, indeed, if all five buzzers sounded together, the receiver responded to them all at the same time, so that a person in another room or in another house, with the receiver at his ear, might hear exactly what those did who were in the same room with the buzzers. The wires from the receiver were connected with the coil in each buzzer so as to get the induced current, as shown in detail in Fig. 160.

We took a telephone induction coil (Fig. 162) and fastened it to a board as represented in Fig. 163, I. One wire of the primary circuit was fastened to the binding post a. The other wire from the primary coil passed to the switch S and then to the battery. From the battery the wire ran to the binding post b. C is a steel tuning fork. The secondary circuit is closed through a telephone receiver. These wires are extended so that the receiver is too far distant for the tuning fork to be heard through the air. When the switch S is closed the tuning fork acts as the interrupter for the primary circuit, and it interrupts according to its time of vibration. If, for instance, the fork gives the tone of middle C on the piano it vibrates 256 times a second. It interrupts the primary circuit 256 times a second. It induces an alternating current of the same frequency in the secondary circuit. The diaphragm of the telephone receiver vibrates in perfect time with the tuning fork and produces the same tone as the tuning fork. We had a series of tuning forks giving a variety of tones, which we could substitute one after another in place of this one. The receiver reproduced accurately the tone of each one of them.

We took a small induction coil (Fig. 164) c and fastened one end of the primary circuit to a battery, B. The wire at the other end of the primary circuit was bent into a hook h. This hook was adjusted about a quarter of an inch from the end of the iron core of the coil. The other wire from the battery was attached to the steel strings of a piano, P. When the coil c was brought over a string and the hook h was allowed to pass beneath the string and touch it very gently, the primary circuit was closed through the string, which served as an interrupter of the current and vibrated according to its tone. The secondary coil, not represented in the figure, was connected to a distant telephone receiver, which reproduced the tones of the piano strings.