Part 15

LIGHTING A SUMMER CAMP BY ELECTRICITY

Summer had arrived. The Science Club had held its last meeting for the season. Harold had engaged three other boys to spend the summer at the farm. I had the roof of an old mill reshingled and gave it to them for a camp. They were to make it over inside. I sent the boys to the country as early as it was possible for them to get away. It would be six weeks later before I could follow them.

When I did arrive I found they had elaborate schemes indeed. The first floor of the mill had been partitioned off into rooms, as shown in diagram (Fig. 107), a, b, c and d being bedrooms; e was a wash room, the like of which has never been seen before. It had not occurred to me that the mill pond m, which came to the very corner of the building, would furnish the boys a complete system of city water-works. At g, in the corner of this room, they had cut a hole in the floor and nailed slats across upon the under side of the timbers, making a depressed floor for a shower bath. This was directly over a stream of water which issued from the mill pond. Hanging from the ceiling over this spot was the nozzle of a garden hose. The other end of this hose ran into the mill pond. The nozzle was capable of delivering either a stream or a shower, according to which way it was twisted in its socket. It was also capable of shutting off entirely the flow of water. The boys asked me to hold my hand in the shower, and to my astonishment it was warm. "What, pray, is your heating system?" I inquired. They invited me to go and see. Moored outside in the mill pond at the corner of the building was our motor boat, which the boys were allowed to use freely and which they understood as well as any one.

They said that ordinarily they used for the shower the cool water of the lake, which they much preferred, and which ran of its own accord, the lake being a trifle higher than the nozzle of the shower, but knowing my antipathy for the cold bath they had slipped the end of the rubber hose over the outlet pipe of the pump which served to cool the gasolene engine in the boat. The engine uncoupled from the propeller was heating and pumping water for my shower bath, and I immediately accepted the invitation to enjoy it.

Certainly no bath was ever more delightful than that one, coming, as it did, at the close of a hot, dirty ride from the city.

I had hastened the bath, because it was already dusk and I had no candle at the mill, but suddenly the room lighted up as if by magic. I saw then what had before escaped my notice, a miniature electric lamp, six-volt, two-candle-power, tungsten, such as are used for tail lights on automobiles. Since tungsten requires about 1.25 watts per candle-power it was a 2.5-watts lamp, and since it was adapted to six volts it would take about four tenths of an ampere.

6 volts × .4 ampere = 2.4 watts. The little wire filament looked to be about 1.5 inches long. Its resistance must have been 15 ohms.

6 volts/15 ohms = .4 ampere.

A battery of five cells was used to furnish electric current for the lamp. Lamps were installed in the bedrooms also and were not intended to be used more than half an hour at a time. Dry battery cells are excellent for this purpose, and for so small a current the cheapest dry cells are as good as the more expensive ones. These cost fifteen cents a cell. They were connected by short pieces of bare copper wire; No. 18 "in series," as shown in Fig. 109. A wire ran from the central (carbon) binding post of one cell to the marginal (zinc) binding post of the next cell. This battery was placed on a shelf in a convenient place. A bare copper wire, No. 18, was attached to the carbon post at one end of the battery and another to the zinc post at the other end of the battery, and these two wires ran to all the rooms where lamps were placed. The wires were fastened up on the walls by staples, taking care that they should nowhere come in contact with each other and "short circuit" the battery. Whenever it was necessary for one wire to cross another, small pieces of pasteboard were tacked up to prevent their touching each other. The lamps L (Fig. 109) were connected to these wires "in parallel." They cost forty cents apiece, and the miniature sockets, into which they were screwed, cost five cents each. One of these sockets was screwed to the side of the door casing in each bedroom. Wires were attached to the line wires, simply by twisting them together. One of these came down to one side of the socket and the other came to the other side of the socket through a switch, s, made of a strip of sheet zinc. The cost of the entire installation was as follows:

5 dry cells at 15c .75 5.2 cp., 6-volt tungsten lamps at 40c 2.00 5 miniature wall sockets at 5c .25 Wire, etc. .20 ---- $3.20

Suppose each lamp is used thirty minutes a day for 100 days, making a total of fifty hours. There are five lamps, making a total of 250 lamp hours. Each lamp takes .4 of an ampere, making a total of 100 ampere hours. The lamps are operated at six volts, making a total of 600 watt hours.

100 days .5 an hour each day --- 50 hours 5 lamps --- 250 lamp hours .4 ampere for each lamp --- 100 ampere hours 6 volts --- 600 watt hours

This amount of electrical energy would cost six cents if generated by a dynamo. It is generally stated that electricity costs fifty times as much if generated by battery as by dynamo. In this case the battery actually did serve for the whole season of 100 days and was not exhausted at the end of the season.

Indeed, since that season, the boys have found that battery cells which had been too much exhausted for use on the engine served very well on the lamps. By use the cells lose, not much in voltage, but in the ability to furnish sufficient quantity in amperes to make the hot spark required for igniting the mixture of gasolene and air in an engine cylinder. When they have been discarded for use with the engine they may still furnish the small amount of current required for the lamps--provided not too many lamps are used at one time.

The dynamo current is always surprisingly cheap when compared with that produced by a battery, but, on the other hand, we are never as economical in the use of the dynamo current as we are with that of the battery.

If all five of the lamps in the above equipment were lighted at the same time and kept burning for half an hour, the battery would run down rather badly and would not fully recover. But if one only is used at a time and for not more than thirty minutes, or if more than one is used at a time and for a proportionately shorter period, the battery will receive no damage.

Dry battery cells may be purchased for either twenty-five cents or fifteen cents each. The chief difference is that the former are capable of giving larger current than the latter, when working against very small resistance. For example, the former may give twenty to twenty-five amperes on a short circuit, that is, connected directly with the ammeter without other resistance, while the latter may give not more than six to ten amperes under similar conditions. For most purposes, other than igniting gasolene engines, in which dry cells are used, an exceedingly small current is required. The electric bell, for example, may not require more than .2 of an ampere and that intermittently. Now it is found by experience that the dry cells which are only capable of furnishing on short circuit six to ten amperes will last quite as long in bell work as one which may give on short circuit twenty to twenty-five amperes. Hence it is good economy to buy them.

"What a fine sitting room you have here! (Fig. 107, f.) When do you expect to fit it up?" said I. Instantly reminding myself, however, that boys do not want a sitting room, I inquired what they intended to use this fine, large room for. They told me that they had plans for making a machine shop out of that. The idea had been suggested by a counter shaft which still hung from the ceiling, and they had discovered that the old mill wheel would still roll over if the penstock were repaired. I replied that I would see what could be done about that sometime.

On the next day matters concerning the motor boat engaged our attention.

HOW ELECTRICITY FEELS

What is more fickle and yet more fascinating than a motor boat? On the morning after my arrival at Millville the boys wanted me to go out with them in the motor boat on the mill pond, as our beautiful little lake is called.

Each one took a hand at trying to start the boat, but although she had acted perfectly well the day before, on this morning no one could get a single explosion. The switch was closed. The gasolene was turned on. The carburetor valves were set at the mark. The spark coils responded with their familiar buzz. She had been primed and, when she had refused to respond to this treatment, the pet valves were opened and the wheel rolled over several times to sweep out the cylinders. But absolutely nothing moved her--neither coaxing nor gibes. Suddenly some one rolled the wheel over for the five-hundredth time and she started and behaved well all day.

All this would not have given us the slightest aggravation if we could only have found out what was the matter and what it was we finally did to correct it. But this we shall probably never know, and hence we are worshippers of the motor boat while we continue to distrust it and complain of it.

While the boat was running one of the boys noticed that a binding post at the end of one of the spark plugs seemed to be loose. He inadvertently put out his hand to tighten it and received a terrific shock. This raised the question among the boys, why one gets a shock from some of the binding posts in the electrical equipment but not from others. I suggested that we run in and call at the house to get my portable measuring instrument (Fig. 110) and a little lunch, and then go up to the upper end of the lake and take our time in examining the electrical equipment of the boat.

The engine had two cylinders. There were two batteries--one for each cylinder. Each battery consisted of five dry cells like the one represented in Fig. 111.

"Now, why don't I feel the electricity when I touch the binding posts of this dry cell?" inquired one of the boys as he handled one of the cells which we had taken out. "Well, I'll give you two reasons why do you not feel it," said I. "First, because you were touching only one binding post at a time. You must touch both of the binding posts of the battery cell at the same time, so that the electric current may pass from one post to the other through your body. Second, even when you do touch both binding posts at the same time you feel no current, simply because you offered probably about 100,000 ohms of resistance to the passage of the current and inasmuch as the one cell exerts only 1.5 volts of pressure, it could send only about .0000015 of an ampere through you. This you cannot feel.

(1.5 volts)/(100,000 ohms) = .0000015 amperes.

"I now connect my instrument as a volt meter between the binding posts of the cell and you see it indicates 1.5 volts, and when I connect it for an instant as an ammeter you see it indicates twenty amperes. That is twice as much as they use for executing criminals by electricity. So you see if you could reduce your resistance sufficiently this one battery cell might kill you. Some people have less resistance than others. The resistance of the body is chiefly in the outer skin. If one's hands are dry and his skin has been made tough and horny by hard work, he has many times the resistance of one whose hands are moist and whose skin is thin and tender.