is called an electrolytic cell, and when it is used to generate an
electric current it is called a battery cell. In either case the
electrolyte is decomposed and put through a chemical change, though the
chemical action in one case is the reverse of that in the other, and
the direction of the electric current in one case is the reverse of
that in the other. For example let us consider the case of a zinc rod
and a carbon rod immersed in sulphuric acid and the external circuit
closed. The current passes as indicated by the arrows in Fig. 151, and
the chemical actions result in hydrogen leaving the sulphuric acid and
zinc taking its place, forming zinc sulphate. This is a white salt and
for purposes of this experiment must remain dissolved in water. So far
we have been considering a generator of electricity--a battery cell. We
may introduce something at _m_, say a motor, which will indicate that
an electric current is flowing. At length the cell ceases to generate
current and is, as we say, "run down." Suppose now we substitute a
dynamo in place of the motor in this circuit, connecting it so that the
carbon rod shall be its positive pole and the zinc its negative pole.
We now call this an electrolytic cell, (Fig. 152). The current will
decompose the zinc sulphate. The zinc will be coated upon the zinc rod
and hydrogen will be procured from the water present, of which it is a
constituent, to form again sulphuric acid as originally.
[Illustration: Fig. 151]
[Illustration: Fig. 152]
We shall thus restore the conditions which prevailed in the first case
as represented in Fig. 151. H_{2}SO_{4} is the chemist's designation
of sulphuric acid and ZnSO_{4} is his expression for zinc sulphate.
The experiment illustrates a storage battery so called. It might better
be called a chemical transformer.
It is wholly unnecessary that one rod be composed of zinc. If we
begin with both rods of carbon immersed in a solution of ZnSO_{4},
and send into this cell the dynamo current, the carbon which acts as
the negative pole will be coated with zinc in a short time, and we
shall have in effect a rod of zinc and one of carbon as before. After
a minute or two we may disconnect the generator and substitute in its
place a bell as indicator, and it will ring, showing that we have
transformed electrical energy into chemical energy which is now being
retransformed into electrical energy. We say that we store electricity
by this means, which is, however, no more true than that a farmer
stores his farm in the bank when he sells it and deposits the money
until he shall need it to buy another farm.
Here is a very beautiful blue salt. I will drop a few crystals of it
into a tumbler of water and dip in two carbon pencils connected to the
dynamo current, using between fifty and sixty ohms of resistance in
the circuit so as to have two amperes flowing. After a minute or two I
lift out the negative carbon and you see that it is well plated with
copper. The blue salt is copper sulphate. If we weigh the negative
carbon, both before and after the experiment, we shall find that copper
has been depositing at the rate of one ounce in twelve hours. If we
reduce the current one half, making it one ampere, it will deposit
copper at the rate of one ounce in twenty-four hours. One ampere will
separate three ounces of lead in a day from a solution of any lead
salt; it will separate .9 ounce of iron in a day from a solution of
any iron salt, and it will liberate from water, which is a compound of
hydrogen, one gallon of the gas in ten hours. The amount of chemical
action is a measure of the amount of electrical energy expended. Before
the present form of commercial wattmeter was devised electrolytic cells
were used to determine what the consumer's bill for electricity should
be each month. These chemical meters contained a solution of zinc
sulphate for the electrolyte and both the positive and the negative
plates were of zinc. While the current is passing, zinc from the
solution is coated upon the negative plate and zinc from the positive
plate takes its place in the solution, thus maintaining a constant
strength of solution.
Here are three iron nails. I propose that you plate one with zinc
and another with copper and then expose all three to the weather
and see which will rust. I propose that you replate all the spoons
at the cottage and the metal tops of the salt cellars with silver.
Electro-plating results better if done slowly. Ten volts and .1 ampere
will be sufficient current.
In the storage battery we generally use lead for both positive and
negative plates and dilute sulphuric acid for the electrolyte. Hydrogen
is liberated at the positive plate and oxygen unites with the negative
plate. When the charging current is cut off the chemical action
reverses, and an electric current is produced by the cell.
In all other batteries there is a destruction of one plate and of the
electrolyte, which cannot be fully restored by a charging current,
although in the case of the lead and sulphuric acid combination the
charging and discharging of the cell may go on alternately for a very
long period without permanent change or loss of any substance except
water. There is, however, plenty of loss of energy in this as in other
transformers. One hundred ampere hours of current expended to charge
a storage battery will yield from seventy-five to eighty-five ampere
hours while the battery is discharging.
The lead storage battery is, however, full of disappointments for
those who do not properly care for it. It is irretrievably ruined if
neglected and allowed to charge too far, or discharge too far, or
evaporate too much water, etc. The voltage of a lead cell must not rise
above 2.2 nor fall below 1.8. It must not be allowed to furnish at any
one time a greater number of amperes than it is rated for. It must
not stand idle too much. It must not be cleaned up and put away for a
period. In fact, the lead-sulphuric acid battery is so poorly adapted
to our need that I feel disposed to try Mr. Edison's new storage
battery. This has nickel hydrate packed in tubes of metallic nickel for
the positive plates and iron oxide pressed into pockets in a sheet of
metallic iron for the negative plate. A solution of potassium hydrate
in water is used for the electrolyte. This is said to be uninjured by
being emptied out and left idle, as our batteries must be for a large
part of the year. The e. m. f. of this battery is less than that of the
lead battery, being only 1.2 volts. We shall therefore need ninety-six
cells (type _B-4_) for the machine shop and ninety-one cells of the
same kind for the cottage. Our dynamo will be unable to charge at one
time more than sixty of these cells connected in series.
The particular chore which you boys must perform is to see that the
voltage of these batteries is maintained at about 1.2. It should
be charged up to 1.8 volt at least once a week and never allowed
to discharge to a lower pressure than one volt. The level of the
electrolyte must be maintained one half inch above the plate by adding
distilled water occasionally.
A few years ago every student of chemistry was more or less agitated
by the thought that more than half of every clay bank was composed
of metal nearly as valuable, or at least as costly, as gold. This
is aluminum. By all the methods then known it was a very difficult
and expensive process to extract the metal from the clay. At length,
by the perfecting of the dynamo, the chemist had under his control
great and powerful electric currents which enabled him to unlock any
chemical compound however refractory and isolate its elements. As a
result aluminum became common enough and cheap enough for even kitchen
utensils.
The metal calcium which a short time ago was an exceedingly rare
substance worth $40 an ounce is now fairly abundant and cheap for
chemical experiments, although it has no qualities which will give it
an extended use.
Powerful electric currents, such as are obtained at Niagara, enable us
to combine elements into hitherto unknown chemical compounds. Carbon
and silicon are made to unite to form carborundum, which vies with the
diamond for hardness. Carbon and calcium unite to form calcium carbide,
used with water to form acetylene gas.
In such processes the intense heat of the electric arc--perhaps 6000
degrees--is employed, together with the electrolytic action of the
current, to separate and combine substances. Enormous currents are used
in the electric furnaces for producing chemical reactions--from 1000 to
30,000 amperes at a time.
Electric currents passing through the human body expend their energy
partly in heat and partly in electrolysis. So simple and harmless a
thing as common salt would become a virulent poison if it could be
electrolized in the body into its elements _sodium_ and _chlorine_.
Let us make use of an electric current to decompose water into its
elements, hydrogen and oxygen. I have a three-ounce wide-mouthed
bottle (Fig. 153) and through its cork I pass two short pieces of No.
24 platinum wire by pushing a stout needle through first. I fill this
bottle with pure water and cut a slight furrow in the side of the
cork, where water may drip out when the gas is produced in the bottle.
We crowd the cork firmly into the mouth of the bottle and invert it.
No water drops out. We bend the ends of the platinum wires into hooks
and hang upon them the wires bringing the dynamo direct current. There
is no evidence of chemical action. Pure water is an exceedingly poor
conductor of electricity. Let us now put about fifty-five ohms of
resistance into the dynamo circuit, so that it will pass about two
amperes, and put a very small pinch of salt into the water, which makes
it so good a conductor that its resistance may be ignored. When now
we close the circuit, as before, a brisk effervescence takes place.
Bubbles of gas rapidly form on the platinum wires and break away,
rising through the liquid. Twice as many form on the negative wire as
on the positive one. As these gases rise to the top of the bottle an
equal volume of the water drips out through the small hole in the cork.
[Illustration: Fig. 153]
Two amperes of electricity will liberate two fluid ounces of hydrogen
at the negative pole and one fluid ounce of oxygen at the positive
pole, in five minutes. Hence in five minutes the bottle should be
full of a mixture of two gases, two thirds of which, by volume, is
hydrogen and one third oxygen. We will catch the water which drips out
so that we may measure it. The bottle being now full of gas I shut off
the current, and removing the cork I bring a flame to its mouth. A
very loud and startling explosion takes place. We pour the water back
into the bottle, and it seems to fill it as well as before. We have
decomposed a few drops of water--not enough to measure--into two gases,
one of which, the hydrogen, occupied two thirds of the bottle, and the
other, oxygen, occupied the remaining third. At ordinary temperatures
they would not reunite, but when raised to their kindling temperature
they united, producing light, heat, a loud noise, and the few drops of
water which had been originally decomposed by the current.
This is the electrolysis of water. I wonder if any such chemical action
took place in Ernest's body when he received that severe shock on the
motor boat the other day.
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.
[Illustration: Fig. 154]
[Illustration: Fig. 155]
"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."
[Illustration: Fig. 156]
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.
[Illustration: Fig. 157]
[Illustration: Fig. 158]
[Illustration: Fig. 159]