ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING
DECOMPOSING LIQUIDS.--During the earlier experiments in the field of
electricity, after the battery or cell was discovered, it was noted that
when a current was formed in the cell, the electrolyte was charged and
gases evolved from it. A similar action takes place when a current of
electricity passes through a liquid, with the result that the liquid is
decomposed--that is, the liquid is broken up into its original
compounds. Thus, water is composed of two parts, by bulk, of hydrogen
and of oxygen, so that if two electrodes are placed in water, and a
current is sent through the electrodes in either direction, all the
water will finally disappear in the form of hydrogen and oxygen gases.
MAKING HYDROGEN AND OXYGEN.--During this electrical action, the hydrogen
is set free at the negative pole and the oxygen at the positive pole. A
simple apparatus, which any boy can make, to generate pure oxygen and
pure hydrogen, is shown in Fig. 89.
It is constructed of a glass or earthen jar (A), preferably square, to
which is fitted a wooden top (B), this top being provided with a
packing ring (C), so as to make it air-tight. Within is a vertical
partition (D), the edges of which, below the cap, fit tightly against
the inner walls of the jar. This partition extends down into the jar a
sufficient distance so it will terminate below the water level. A pipe
is fitted through the top on each side of the partition, and each pipe
has a valve. An electrode, of any convenient metal, is secured at its
upper end to the top of the cap, on each side of the partition. These
electrodes extend down to the bottom of the jar, and an electric wire
connects with each of them at the top.
[Illustration: _Fig. 89._ DEVICE FOR MAKING HYDROGEN AND OXYGEN]
If a current of electricity is passed through the wires and the
electrodes, in the direction shown by the darts, hydrogen will form at
the negative pole, and oxygen at the positive pole. These gases will
escape upwardly, so that they will be trapped in their respective
compartments, and may be drawn off by means of the pipes.
PURIFYING WATER.--Advantage is taken of this electrolytic action, to
purify water. Oxygen is the most wonderful chemical in nature. It is
called the acid-maker of the universe. The name is derived from two
words, _oxy_ and _gen_; one denoting oxydation, and the other that it
generates. In other words, it is the _generator of oxides_. It is the
element which, when united with any other element, produces an acid, an
alkali or a neutral compound.
RUST.--For instance, iron is largely composed of ferric acid. When
oxygen, in a free or gaseous state, comes into contact with iron, it
produces ferrous oxide, which is recognized as rust.
OXYGEN AS A PURIFIER.--But oxygen is also a purifier. All low forms of
animal life, like bacteria or germs in water, succumb to free oxygen. By
_free oxygen_ is meant oxygen in the form of gas.
COMPOSITION OF WATER.--Now, water, in which harmful germs live, is
one-third oxygen. Nevertheless, the germs thrive in water, because the
oxygen is in a compound state, and, therefore, not an active agent. But
if oxygen, in the form of gas, can be forced through water, it will
attack the germs, and destroy them.
COMMON AIR NOT A GOOD PURIFIER.--Water may be purified, to a certain
extent, by forcing common air through it, and the foulest water, if run
over rocks, will be purified, in a measure, because air is intermingled
with it. But common air is composed of four-fifths nitrogen, and only
one-fifth oxygen, and, as nitrogen is the staple article of food for
bacteria, the purifying method by air is not effectual.
PURE OXYGEN.--When, however, oxygen is generated from water, by means of
electrolysis, it is pure; hence is more active and is not tainted by a
life-giving substance for germs, such as nitrogen.
The mechanism usually employed for purifying water is shown in Fig. 90.
A WATER PURIFIER.--The case (A, Fig. 90) may be made of metal or of an
insulating material. If made of metal it must be insulated within with
slate, glass, marble or hard rubber, as shown at B. The case is provided
with exterior flanges (C, D), with upper and lower ends, and it is
mounted upon a base plate (E) and affixed thereto by bolts. The upper
end has a conically-formed cap (F) bolted to the flanges (C), and this
has an outlet to which a pipe (G) is attached. The water inlet pipe (H)
passes through the lower end of the case (A). The electrodes (I, J) are
secured, vertically, within the case, separated from each other
equidistant, each alternate electrode being connected up with one wire
(K), and the alternate electrodes with a wire (L).
[Illustration: _Fig. 90._ ELECTRIC WATER PURIFIER]
When the water passes upwardly, the decomposed or gaseous oxygen
percolates through the water and thus attacks the germs and destroys
them.
THE USE OF HYDROGEN IN PURIFICATION.--On the other hand, the hydrogen
also plays an important part in purifying the water. This depends upon
the material of which the electrodes are made. Aluminum is by far the
best material, as it is one of nature's most active purifiers. All clay
contains aluminum, in what is known as the sulphate form, and water
passing through the clay of the earth thereby becomes purified, because
of this element.
ALUMINUM ELECTRODES.--When this material is used as the electrodes in
water, hydrate of aluminum is formed, or a compound of hydrogen and
oxygen with aluminum. The product of decomposition is a flocculent
matter which moves upwardly through the water, giving it a milky
appearance. This substance is like gelatine, so that it entangles or
enmeshes the germ life and prevents it from passing through a filter.
If no filter is used, this flocculent matter, as soon as it has given
off the gases, will settle to the bottom and carry with it all
decomposed matter, such as germs and other organic matter attacked by
the oxygen, which has become entangled in the aluminum hydrate.
ELECTRIC HAND PURIFIER.--An interesting and serviceable little purifier
may be made by any boy with the simplest tools, by cutting out three
pieces of sheet aluminum. Hard rolled is best for the purpose. It is
better to have one of the sheets (A), the middle one, thicker than the
two outer plates (B).
[Illustration: _Fig. 91._ PORTABLE ELECTRIC PURIFIER]
Let each sheet be 1-1/2 inches wide and 5-1/2 inches thick. One-half
inch from the upper ends of the two outside plates (B, B) bore bolt
holes (C), each of these holes being a quarter of an inch from the edge
of the plate. The inside plate (A) has two large holes (D) corresponding
with the small holes (C) in the outside plates. At the upper end of this
plate form a wing (E), 1/2 inch wide and 1/2 inch long, provided with a
small hole for a bolt. Next cut out two hard-rubber blocks (F), each
1-1/2 inches long, 1 inch wide and 3/8 inch thick, and then bore a hole
(G) through each, corresponding with the small holes (C) in the plates
(B). The machine is now ready to be assembled. If the inner plate is 1/8
inch thick and the outer plates each 1/16 inch thick, use two small
eighth-inch bolts 1-1/4 inches long, and clamp together the three
plates with these bolts. One of the bolts may be used to attach thereto
one of the electric wires (H), and the other wire (I) is attached by a
bolt to the wing (E).
[Illustration: _Figs. 92-95._ DETAILS OF PORTABLE PURIFIER]
Such a device will answer for a 110-volt circuit, in ordinary water. Now
fill a glass nearly full of water, and stand the purifier in the glass.
Within a few minutes the action of electrolysis will be apparent by the
formation of numerous bubbles on the plates, followed by the
decomposition of the organic matter in the water. At first the
flocculent decomposed matter will rise to the surface of the water, but
before many minutes it will settle to the bottom of the glass and leave
clear water above.
PURIFICATION AND SEPARATION OF METALS.--This electrolytic action is
utilized in metallurgy for the purpose of producing pure metals, but it
is more largely used to separate copper from its base. In order to
utilize a current for this purpose, a high ampere flow and low voltage
are required. The sheets of copper, containing all of its impurities,
are placed within a tank, parallel with a thin copper sheet. The impure
sheet is connected with the positive pole of an electroplating dynamo,
and the thin sheet of copper is connected with the negative pole. The
electrolyte in the tank is a solution of sulphate of copper. The action
of the current will cause the pure copper in the impure sheet to
disintegrate and it is then carried over and deposited upon the thin
sheet, this action continuing until the impure sheet is entirely eaten
away. All the impurities which were in the sheet fall to the bottom of
the tank.
Other metals are treated in the same way, and this treatment has a very
wide range of usefulness.
ELECTROPLATING.--The next feature to be considered in electrolysis is a
most interesting and useful one, because a cheap or inferior metal may
be coated by a more expensive metal. Silver and nickel plating are
brought about by this action of a current passing through metals, which
are immersed in an electrolyte.
PLATING IRON WITH COPPER.--We have room in this chapter for only one
concrete example of this work, which, with suitable modifications, is an
example of the art as practiced commercially. Iron, to a considerable
extent, is now being coated with copper to preserve it from rust. To
carry out this work, however, an electroplating dynamo, of large
amperage, is required, the amperage, of course, depending upon the
surface to be treated at one time. The pressure should not exceed 5
volts.
The iron surface to be treated should first be thoroughly cleansed, and
then immediately put into a tank containing a cyanide of copper
solution. Two forms of copper solution are used, namely, the cyanide,
which is a salt solution of copper, and the sulphate, which is an acid
solution of copper. Cyanide is first used because it does not attack the
iron, as would be the case if the sulphate solution should first come
into contact with the iron.
A sheet of copper, termed the anode, is then placed within the tank,
parallel with the surface to be plated, known as the cathode, and so
mounted that it may be adjusted to or from the iron surface, or cathode.
A direct current of electricity is then caused to flow through the
copper plate and into the iron plate or surface, and the plating
proceeded with until the iron surface has a thin film of copper
deposited thereon. This is a slow process with the cyanide solution, so
it is discontinued as soon as possible, after the iron surface has been
completely covered with copper. This copper surface is thoroughly
cleaned off to remove therefrom the saline or alkaline solution, and it
is then immersed within a bath, containing a solution of sulphate of
copper. The current is then thrown on and allowed so to remain until it
has deposited the proper thickness of copper.
DIRECTION OF CURRENT.--If a copper and an iron plate are put into a
copper solution and connected up in circuit with each other, a primary
battery is thereby formed, which will generate electricity. In this
case, the iron will be positive and the copper negative, so that the
current within such a cell would flow from the iron (in this instance,
the anode) to the negative, or cathode.
The action of electroplating reverses this process and causes the
current to flow from the copper to the iron (in this instance, the
cathode).