The
Science Notebook
Gilbert Chemistry - Part 10
NOTE:
This book was
published in 1936 as a manual to accompany several Gilbert Chemistry
sets of the time. While some of the
experiments and activities here may be safely done as written, a
number of them use chemicals and methods no
longer considered safe. In addition, much of the
information contained in this book about chemistry and other subjects
is outdated and inaccurate. Therefore, this book is probably best
appreciated for its historical value rather than as a source for
current information and good experiments. If you try
anything here, please understand that you do so at
your own risk.
See our Terms
of Use.
Pages 181 - End
GILBERT CHEMISTRY 181
from this jar into one of the other two jars, being careful not to allow any of the liquid to get into this jar. Figure 37.
Now
seal the two iars containing the sprouted beans or peas and allow them
to stand for several days in the sunlight. Label the one
containing the carbon dioxide. Examine the jars from time to time
and notice that the plants in the jar containing the carbon dioxide
grow faster than those in the other jar. This proves that carbon
dioxide is essential to plant growth.
A SIMPLE PHOTOCHEMICAL EXPERIMENT TO DETERMINE THE ACTIVITY OF THE ENERGY OF THE SUN'S RAYS
EXPERIMENT 619 (Sodium nitroprusside and thiouroa purchased separately)
Four test tubes are numbered and placed in a rack so that equal exposure to light may be secured.
In
tube one is placed one-quarter of a test tube each of the three
solutions sodium nitroprusside, sodium bicarbonate, and thiorea. In tube two is placed one-quarter of a
test tube each of the sodium nitroprusside and sodium bicarbonate
solutions only. In tube three is placed one-quarter of a
test tube each of the thiourea and sodiurn bicarbonate solutions
only. In the last tube one-quarter of a test tube of sodium
nitroprusside and one-quarter of a test tube of thiourea solution are
mixed.
the four tubes are then placed in the sunlight for
from four to six minutes. A blue color will form quickly in tube
one and slowly in tube four, number two will darken slightly, and tube
three will remain unchanged. The reaction will proceed in
ordinary light, but at a much slower rate.
The tubes are
removed from the sunlight as soon as one and four are distinctly blue,
and one-quarter test tube of thiourea solution is added to tube two. A
blue coloration will take place quickly without the aid of further
exposure to light. One-quarter test tube of nitroprusside
solution is then added to tube three. The blue color will not be formed
in this case, showing that the sunlight does not cause any change with
thiourea in sodium bicarbonate solution.
182 GILBERT CHEMISTRY
The
tubes are now placed in total darkness for a period of three to six
hours or more. Upon removal it will be noted that tubes one two
have changed to a deep crimson, tube four will be blue and practically
unchanged, while tube three will be colorless, although all the
necessary reagents for the reaction have been present for several
hours.
If one-quarter of a test tube of sodium
bicarbonate solution is added to tube four, the blue color immediately
takes on a purplish tint and if kept in the dark the color will be
decidedly red after about one-half hour, showing that the tube "stored
darkness" even though it was not apparent, as in tubes one and two,
until the sodium bicarbonate addition.
All the tubes are
then re-exposed to sunlight and the blue coloration will immediately
form in each, since all the reactants are now present in each
tube. Another period of darkness will bring the red, etc., until
finally the active ingredients are decomposed, due to side
reactions. If too long exposures to sunlight are avoided after
the blue color is produced, the reaction may be reversed 12 to 20
times. lf the solution is placed
in a completely filled,
sealed container, the change blue to red will fail to take place after
several times, showing that the presence of air is necessary, probably
for the spontaneous re-oxidation of the iron previously reduced by the
action of the sunlight.
The solutions required are:
one-half oz. of freshly prepared 0.5% sodium nitroprusside (to be kept
in an opaque bottle;) one-half oz. of saturated sodium bicarbonate; and
one-half oz. of 0.5% thiourea.
"COLD LIGHT," OR LIGHT BY CHEMICAL ACTION
EXPERIMENT 620-A demonstration of "chemiluminescence"
One
of the most beautiful and striking demonstrations for laboratory or
lecture work is that of chemiluminescence or “cold light."
Certain chemical reactions, usually ones involving the oxidation of an
organic compound, result in the development of light without other
visible reaction. Even heat, which is usually associated with
light of any kind, is noticeably absent.
This phenomenon
of chemiluminescence has long been known, but has not previously
been employed extensively because of difficulties encountered in the
available reactions. These were complex and dangerous, produced
only a limited luminescence, or required reagents not readily
obtainable. But now three-aminophthalhydrazide has
been made
available which overcomes all of these obiections. The reaction
is simple, safe, and develops light of intense brilliancy.
LUMINOL
The
name "luminol" has recently been applied to this compound in place of
its chemical name for convenience, to associate with it the property of
luminescence.
The demonstration requires only the
oxidation of luminol in dilute alkaline solution with three per cent
alkaline hydrogen peroxide and a second oxidizing agent. All four
compounds are necessary in the solution to obtain the strongest
radiation. Almost
GILBERT CHEMISTRY 183
innumerable
variations can be used in the actual procedure, from the mere mixing
of the required chemicals to very elaborate displays. A few
of the simpler methods are given to serve as guides.
For
small audiences or laboratory demonstration, the flask method is the
most satisfactory. In a two-liter long-necked flask, a small
quantity of luminol on the point of a knife blade is dissolved in a
test tube full of five per cent sodium hydroxide and diluted to two
quarts with water. In a similar flask, two knife blade portions
of potassium ferrocyanide is dissolved in water, a test tube full of
three per cent hydrogen peroxide added and diluted to two quarts with
water. When both solutions are ready and the room is darkened,
one flask is grasped in each hand and the contents of them poured
simultaneously through a funnel into a six-liter flask. The
reaction starts as soon as the liquids mix in the funnel. After
the initial development of the light has begun, the flask is swirled
and a small quantity of solid potassium ferricyanide added. The
brillliance is increased and can be still further intensified by the
gradual addition of five percent sodium hydroxide. At the
concentrations given, the original light intensity is small, but the
increased brilliance obtained by the addition of further reagents is
very beautiful.
For demonstration to larger audiences, it
is more convenient to use a large jar containing about 14 quarts of
water. In a small flask is dissolved one spoon measure of luminol
in five test tubes full of five per cent sodium hydroxide, and in a
second flask, 25 spoon measures of potassium ferricyanide in five test
tubes full of three per cent hydrogen peroxide. To indicate more
clearly the lack of heat in the reaction, the solution may be poured
simultaneously over a cake of ice which has been floated in the
water. The solutions should be allowed to mix in concentrated
form on the ice before being diluted with the surrounding water.
After the reaction mixture has diffused throughout the water, the
solution is stirred vigorously with a glass rod and further potassium
ferricyanide or alkali or both added as desired.
A very
beautiful display may be prepared by means of two fine sprays which are
made to interact some distance above the lecture table. Each
spray of humidifier is connected to a compressed air source and to one
of the stock solutions previously mentioned. Care should be taken
that the spray guns are operating at the same rate. By variation of the
stock solutions, the resulting mist can be changed from a hardly
visible cloud to a brilliant fountain resembling a display of
fireworks.[*]
[*] The reagent "luminol" may be purchased' from the Eastman Kodak Company. Rochester, N. Y.
[184]
PART IV
Electro-Chemistry
Before
we discuss the part electricity takes in chemistry we must first know a
little something about electricity. Electricity, like heat, is a form
of energy. About 100 years ago very little was known about the role
that electricity played in chemical reactions. Today matters are
quite different. Electricity and chemistry are very closely
related, many large and important industrial concerns are engaged in
manufacturing materials involving the use of electro-chemical
reactions.
Today chlorine gas and caustic soda are
manufactured by passing an electric current through salt water.
From the chlorine gas we obtain bleaching powder. Metals are
extracted from their ores by passing a current through their molten or
fused salts. Nickel-plating, copper-plating and gold-plating are
done by passing a current through
a solution containing salts of
these metals. The success of these important industries and many others
is based on the fact that electricity possesses the power of
decomposing chemical compounds.
On the other hand, we can
show the relationship between chemistry and electricity in another
way. We have already said that electricity is a form of
energy. Now, in most chemical reactions, heat is liberated
as the form of energy. However, under proper conditions, the
energy of certain chemical reactions is liberated in the form of
electricity. For example, if we put a copper plate and zinc plate
in a solution containing an acid and connect the two plates with copper
wires we find that a current of electricity is produced. A
reaction takes place in which electricity in the form of energy
liberated. Use is made of this fact in the manufacture of the
different types of electric cells and batteries. Batteries are
simply cells connected together in series in order to produce a
stronger current. There are several types of cells, all of which
come under two classes,
namely, the primary cells, which include
both the dry and wet cells, and the secondary cell or storage battery,
as it is called.
Finally, we will mention a third
relationship of electricity to chemistry. That is, the part electricity
plays in furnishing heat to produce chemical change. A good
example of this is the manufacture of graphite from carbon by means of
the electric furnace. Also the manufacture of calcium carbide for
the production of fertilizers, of nitric acid from nitrogen in the air,
and many other important industries depend upon the heat generated by
the electric current for their success.
Before we discuss
any of the different types of cells we will first consider the parts
that go to make up a primary cell. These are, first, the jar which
holds the solution and the elements; second, the solution of
electrolyte, as it is commonly called; third, the cathode or negative
electrode, which is usually made of the element zinc; and, fourth, the
anode, or positive electrode, which is usually the element carbon.
THE DRY CELL AND HOW IT IS MADE
The
dry cell is a very common type of cell and millions of them are used
for bell, telephone and other purposes. The jar of the dry cell
consists of a cup of sheet zinc which serves as the negative electrode
(Figure 38.) A binding post is fixed at the top of this
cup. The electrolyte in the dry cell consists of an active paste
which consists usually of one part of zinc chloride, one part of zinc
oxide, one part of ammonium chloride or sal ammoniac, three parts of
plaster of Paris, two parts of manganese dioxide and one part of water,
all by weight.
GILBERT CHEMISTRY 185
The
cell is prepared as follows: the zinc cup is filled to within one~half
inch of the top and a carbon rod containing a binding post on the upper
end is pushed down into the paste to within an inch of the
bottom. Melted pitch is then poured over the paste until it is
even with the top of the cup. The pitch is then allowed to cool,
and the cell is ready for use. It is only when you close the
circuit, that is, connect the two binding posts with a wire, that you
start chemical action within the cell. When the circuit is open
the chemical action stops.
HOW THE DRY CELL WORKS
After
the cell is made and copper wire is attached from the carbon post to
the zinc post a current of electricity passes through the wire.
This is due to action of the active paste upon the zinc
electrode. When the circuit is opened, that is, when the carbon
and zinc posts are disconnected, the action stops.
Now
the chemical action which takes place within the cell is as follows:
The ammonium chloride and water react to form hydrochloric acid which
attacks the zinc. The zinc goes into solution in the form of
positive ions, which are atoms or groups charged electricity.
When this happens the zinc electrode assumes an electro negative
condition. The positive zinc ions unite with the negative
chlorine ions of the hydrochloric
186 GILBERT CHEMISTRY
acid
to form zinc chloride with the formation of positive hydrogen
ions. Now, the positive hydrogen ions move to the carbon
electrode where they lose their charge and become gaseous
hydrogen. Therefore, when the circuit is closed the chemical
action, which takes place, keeps the zinc pole or cathode negatively
charged and the carbon pole or anode positively charged. The flow
of electricity is always from the negative zinc pole to the positive
carbon pole through the solution, and from the positive carbon pole to
the negative pole through the wire.
You might ask the
question, What happens to the hydrogen gas when chemical action takes
place within the cell? The hydrogen gas as fast as it is formed
at the carbon electrode is oxidized to water by oxygen from the
manganese dioxide. This brings up the phenomenon known as
polarization. By polarization is meant the cutting
down of
an electric current, due to the lowering of potential between the
carbon and zinc poles. Polarization in a cell is caused by
formation of bubbles of hydrogen gas clinging to the carbon electrode,
thereby producing less surface. To prevent this, manganese
dioxide is used, which, as already stated, oxidizes the hydrogen gas to
water.
THE WET CELL
The
wet cell or other type of primary cell is very similar to the dry cell.
The electrolyte instead of being a paste, as in the dry cell, is a
solution. The positive and negative electrodes are of carbon and zinc or
of copper and zinc. (Figure 39.) The principles involved in the
formation of a current due to chemical action in the wet cell is the
same as that in the dry cell although there are several types of wet
cells.
GILBERT CHEMISTRY 187
THE STORAGE BATTERY
The
second type of electric cell or storage battery is a little more
complicated than the dry or wet cell. The storage battery consists of a
number of secondary cells (Figure 40). It is used largely for
running electric power plants, electric automobiles, telephone and
telegraph work, etc.
The
storage battery does not generate a current of electricity like a
primary cell by a direct chemical action. It is charged by a
current of electricity, after which it will deliver a current until the
cell is run down. The chemcial action taking place when the
electricity is discharged is much more complex in this type of cell, so
that we will not go into a discussion of it.
EXPERIMENT 621 - How to test a battery of dry cells
if
you have two or three dry cells around the house and wish to test their
strength, perform the following experiment with them:
Connect
the cells together in series as shown in Figure 41 by attaching small
pieces of copper wire to the carbon binding post of one cell and zinc
binding post of the other cell. (Figure 41.) Now connect a longer
piece of wire to the free carbon post and another long piece to the
free zinc post. Clean the ends of all the copper wires using with
a knife blade.
Now dissolve two teaspoonfuls of sodium
chloride (table salt) in a tumbler two-thirds full of water and put the
ends of the copper wires, which should be clean, in the solution.
Notice whether bubbles of gas appear on the ends of the wires in the
solution. By setting up the same number of new cells in the same
manner and comparing the amount of gas produced with that produced from
the old cells you can tell whether the old cells are of sufficient
strength to be of value an performing the following experiments.
188 GILBERT CHEMISTRY
If
no gas is formed from the old cells when the preceding experiment is
accurately performed, the cells are worn out and you will have to
obtain some new cells. Two or three dry cells connected in series will
give you sufficient current for performing most of the experiments as
outlined.
EXPERIMENT 622 - How to determine the positive or negative wire
Connect
two or three dry cells together in series as in Experiment 621.
Now moisten a piece of filter paper with a little sodium iodide
solution and place the ends of the wires froin the battery about
one-quarter inch apart on the paper (Figure 42). Notice that the
spot where one of the wires touches the paper becomes brown.
Also
notice that this is the wire connected to the positive or
carbon pole.
What really happened was this: When you
touched the ends of the wires from the battery to the paper containing
sodium iodide solution you simply closed the circuit and a current of
electricity flowed from the positive carbon electrode to the negative
zinc electrode, at the same time decomposing the sodium iodide.
The iodine of sodium iodide being in the form of negative ions is
attracted to the positive wire, where they lose their charge and become
atomic iodine, thereby producing a reddish brown spot. This is a very
convenient way of telling what is the positive and negative wire of any
source of electricity.
EXPERIMENT 623 - Another way to tell the positive and negative wires
Put
two measures of potassium nitrate and two drops of phenolphthalein in a
test tube one-quarter full of water. Shake thoroughly until all the
solid is dissolved. Now moisten a piece of filter paper about one inch
square with some of this solution and test the paper the same way you
did in the preceding experiment. Notice this
GILBERT CHEMISTRY 189
time
that the spot where one of the wires touches the paper becomes
red. Also notice that this wire is the wire connected to the
negative zinc binding post and is therefore the negative wire.
The
potassium ions of the potassium nitrate being positively charged are
attracted to the negative copper wire, where they lose their charges
and become atomic potasssium. Atomic potassium, being a very
active substance, instantly unites with the water to form a base
potassium hydroxide, which turns the phenolphthalein red.
EXPERIMENT 624 - How to show the direction of a current
Dissolve eight measures of nickel ammonium sulphate in a tumbler one-third full of water.
Now
connect two or three dry cells in series as shown in Experiment 621 and
put the ends of the wires leading from the positive and negative poles
of the battery into the nickel solution. Notice that very soon the wire
attached to the negative pole or electrode is coated with metallic
nickel or is being nickel-plated.
Now disconnect the two
wires from the battery and attach the wire which was plated with nickel
to the positive carbon pole and the other wire to the negative zinc
pole. Put the ends of the wires again in the solution. Notice
that the nickel is soon dissolved from the plated wire and is deposited
on the other wire which is attached to the negative pole.
This
proves that the current always flows from the positive pole to the
negative pola and that the metal deposited always follows the direction
of the current.
ELECTROPLATING
The
very simple process of transferring metal from one object to another by
chemical and electrical means is called electroplating. All of the
silverware in use is plated
190 GILBERT CHEMISTRY
by
the same process you are going to use. By this method objects are
copper-plated, silver-plated and gold-plated.
Besides
its use in plating, the process is used in the purification of certain
metals. Copper, for example, is separated from its impurities in
this manner. At a recent chemical exhibit in New York there was
placed on exhibition a slab of copper five feet square and six inches
thick which had been purified not by removing impurities from the
copper, but by removing the copper from the impurities.
In
electroplating, the electrolyte or bath always consists of a solution
of the salt of the metal to be deposited or plated on the object.
Now, as to the action which takes place when an object is
electroplated, let us first consider the nature of solutions of
metallic salts when a current is passed through the solution.
Salts are made up of metallic elements and non-metallic elements or
groups. When in solution the metallic elements become ions and
have positive electric charges. The non-metallic elements or
groups on the other hand also become ions and have negative
charges. Now suppose we pass a current through a solution of
copper sulphate. The metallic copper ions which are positively charged
are attracted to the negative pole to which is attached the object to
be plated. On reaching the object to be plated the copper ions
lose their charge, become atomic or metallic copper and as such are
deposited in a smooth thin layer upon the object.
The
non-metallic sulphate groups which are negatively charged are attracted
to the positive pole to which in the case of copper-plating is attached
a sheet or bar of copper. Upon reaching the positive copper pole
the sulphate groups lose their charge, become molecular sulphate,
having the properties of a strong acid grouping and dissolve the
copper to form copper sulphate which goes into solution. The amount of
copper which goes into solution in this way is exactly equal to the
amount of copper which is deposited upon the object to be plated.
You can see, therefore, that the concentration of the copper sulphate
solution is always the same as long as there is any
copper left at the positive pole.
The preceding action may be expressed a little more clearly in the form of an
equation, thus:
| Salt | electricity = | metal (of salt)
goes to the object to be
plated (cathode -) | non-metal (of salt)
goes to the metallic
plate (anode +)
|
By using different kinds
of salts and plates of different metals we can plate with almost any
metal, although some metals plate easier than others.
EXPERIMENT 625 - How to copper-plate
If
you have any medals which you wish to copper-plate, proceed as outlined
in this experiment. lf not, use a nail, or other iron object.
The
obiect to be plated must always be cleaned of oils, grease or varnish.
This can easily be done by boiling the object in vinegar or a solution
of sodium carbonate for several minutes. When cleaned the obiect
must never be touched with the fingers, for if it is a film of grease
will be left and the plating will not stick to the surface.
Dissolve
one spoonful of copper sulphate in a tumbler half full of water.
Now, using two or three dry cells connected up in series as outlined in
previous experiment, attach the medal or iron object to be
copper-plated to the wire from the zinc pole or negative wire in the
manner illustrated (Figure 43.) To the wire from the carbon or
positive pole of the battery attach the copper strip.
Now
immerse the copper strip and the medal in the copper sulphate solution,
being sure that the medal to plated is below the surface of the
solution. Do not allow the copper strip and medal to touch.
GILBERT CHEMISTRY 191
In
a few minutes you will note that the medal is covered with a deposit of
copper. leave the medal in the solution until an even coat is
deposited. This should take from 10 minutes to one hour,
depending upon the size of the object and the strength of the solution.
To give the medal a bright finish, rub it lightly with an ordinary pencil eraser.
EXPERIMENT 626-How to nickel-plate
The
object to be nickel-plated must be free of oil, grease and
varnish. This can be done by boiling it in vinegar or a solution
of sodium carbonate.
Dissolve one spoonful of
nickel ammonium sulphate in a tumbler half full of water. Now
attach the iron, copper or brass object to be nickel-plated to the
negative wire and an iron nail to the positive wire. Immerse these in
the solution and notice that soon the object attached to the negative
wire which goes to the zinc post is covered with a coating of nickel.
ELECTROTYPING
Electroplating
with copper has been taken advantage of in the printing and publishing
industry. Here it is called electrotyping. This process consists
in making a mold of wax or plaster of Paris and the impression of the
type of a book made by pressing the mold against the type. The
wax is then dusted with graphite, which is a good conductor of
electricity. It is then connected to the negative pole of a
battery and immersed in a copper solution. The positive
pole is a sheet of copper.
When a suitable thickness
of copper is deposited on the impression, the thin sheet of metal is
removed from the wax and "backed," that is, the reversed side is filled
with a low melting substance such as solder or lead.
192 GILBERT CHEMISTRY
It
is now affixed to a rotary, or flat press and used directly for
printing. Besides its use in printing, this process may be used for
making duplicates of medals. Practically all books are now printed
from electrotype plates. Without electrotype plates it would be
necessary to set up new type every time a new edition oi a
book was printed. This would take much more time and would be much
more expensive.
EXPERIMENT 627-How to reproduce a medal
Secure a medal, one as small as possible, or some foreign coin which you would like to reproduce in copper.
Prepare
the molding wax by cutting a square piece of paraffin wax a little
larger than the medal and about one-eighth of an inch in thickness. The
wax may be molded flat by warming slightly and kneading it with the
fingers. Now hold it under cold water until it becomes
hard. Clean the medal and press it down upon the wax with
considerable force. Then remove the medal with a knife
point. If the wax sticks to the metal, oil the medal very, very
slightly.
Now scrape some graphite or lead from a soft
pencil upon the impression in the wax and rub the graphite to a fine
finish with the brush included in the set. lt is essential to
give the impression a compact and smooth surface, therefore, rub with
the brush as long as possible, even 15 minutes. Add more graphite if
necessary until the whole impression is black and shining.
Set
up two or three cells in series and attach the wire from the negative
zinc post to the wax mold, making contact from the wire to the surface
of the impression. (Figure 44.) The contact is made by making a
channel from the wire to the impression as shown in the illustration.
Fill this channel with graphite and pack it tight with a pencil point.
To
the other wire from the positive carbon post of the battery attach the
copper strip. Now place the wax mold and the copper strip about
one inch apart in a tumbler containing a solution of copper
sulphate. The solution of copper sulphate is made by dissolving
one spoonful of copper sulphate in a tumbler half full of water.
Allow
the current to pass through the solution for several hours - over
night, if necessary - and examine the wax mold carefully from time to
time and notice that the copper-plate gradually creeps across the
impression.
When the process is complete and you have a
thin sheet of copper deposited on the impression, remove the wax mold
from the solution, wash it with water and then remove the wax by
melting it in a tin cover. The copper-plate then produced is an exact
reproduction of the medal and can be preserved by pasting it on a piece
Of cardboard.
You may nickel-plate the copper
reproduction by placing it in a solution of nickel ammonium sulphate as
explained in the experiment, "How to nickel-plate."
EXPERIMENT 628 - How to make a bronze statue from a plaster cast
This
is a very interesting experiment in electroplating. Obtain a
small white unpainted plaster statuette or cast and be sure that it is
small enough to fit into a tumbler or pint jar.
Now paint
the statuette with a little linseed oil or quick drying varnish and
allow the oil to dry thoroughly. This makes the statuette waterproof
and forms a skin upon which the powdered graphite will stick. Whm
the oil is dry brush the statuette with
GILBERT CHEMISTRY 193
powdered graphite from your lead pencil. Brush until the surface is smooth and black.
Set
up two or three dry cells in series and wind the end of the wire from
the negative zinc post around the statuette. Attach the copper
strip to the wire from the positive carbon post. Now place the
statuette and copper strip in a copper sulphate solution made by
dissolving one spoonful of copper sulphate in a glass full of
water. Allow the statuette to remain in the solution until it is
evenly coated with copper. This is best done by leaving it to stand
over night.
lf you wish to nickel-plate the bronze cast,
simply place it in a solution of nickel ammonium sulphate, as explained
in the experiment on nickel-plating.
ETCHING BY MEANS OF ELECTRICITY
Pretty
pattems or designs may be duplicated on sheet copper or steel very
easily by means of the electric current. The designs will have
the appearance of being etched.
EXPERIMENT 629 - How to etch on copper.
Take
the copper strip and dip it into hot parafhn. When it is cold, trace
the design you want and then with a toothpick remove the paraffin along
the tracings. Also scrape off the paraffin where connection is to
be made with the wire and copper strip.
Now connect two
or three dry cells in series and attach the wire from the positive
carbon post to the copper strip to be etched. (Figure 45.) To the
wire from the negative zinc post attach a bright nail or other object
of iron. Place the nail and copper strip in a copper sulphate
solution made by dissolving one spoonful of copper sulphate in a
tumbler half full of water.
While the iron nail is being
plated with copper, the copper strip is being corroded. Since
only the bare spaces are affected, the copper will be eaten along the
lines of the tracing. After several hours, remove the copper
strip, melt off the paraffin and notice that the etching is quite
clear. lt will look as though the design were directly engraved upon
the copper.
EXPERIMENT 630 - How to etch on steel
Steel
or iron can be etched the same way as the copper in the preceding
experiment. Procure a piece of sheet steel or iron and after
coating it with paraffin trace the design upon it. Then connect
it to the positive wire leading to the carbon post and attach a bright
nail to the negative wire leading to the zinc post of the battery.
Now
place the steel and the iron nail an a solution of nickel ammonium
sulphate made by dissolving one spoonful of the compound in a tumbler
half full of water. Allow the current to pass throwh the solution
for several hours and then remove the steel and melt off the
paraffin. Notice that the design is etched upon the steel.
194 GILBERT CHEMISTRY
EXPERIMENT 631 - Copper-plating by immersion
Dissolve
two measures of copper sulphate in a test tube half full of water and
place into this solution a small strip of clean steel. Allow the
steel to remain in the solution for half an hour and notice after this
time that it is coated with copper.
The reason for this
is as follows: Some metals, like iron, are more easily dissolved by
acids than others, like copper. Therefore, when iron is placed in a
copper sulphate solution some of the iron goes into solution to form
iron sulphate and an equal amount of copper goes out of solution as
metallic copper and is deposited on the iron.
EXPERIMENT 632 - Tin-plating by contact
Dissolve
six or eight measures of tartaric acid in a tin cup half full of
water. Now place into this solution a penny which has been
cleaned by boiling for several moments in a little vinegar.
Put
the tin cup on the stove and allow the water to boil off. Notice
that after several minutes the penny will gradually become coated with
a bright silvery plating of tin.
EXPERIMENT 633 - Nickel-plating by contact
Heat a test tube two-thirds full of water to boiling and dissolve in it five measures of nickel ammonium sulphate.
Put
a clean penny in a small tumbler and pour the nickel solution upon
it. Then place the strip of zinc included in the set in the
tumbler so that it comes in contact with the penny. Allow the
solution to stand for several minutes and notice after some time that
the penny is gradually coated with nickel.
EXPERIMENT 634 - Formation of a current by contact of copper with zinc
Dissolve
four measures of sodium bisulphate in a test tube full of water and
pour this solution into a tumbler. Drop into the tumbler a clean
penny and notice that the penny is unaffected by the solution.
Then place in the solution the strip of zinc so that it touches the
penny. Notice that bubbles of gas are formed on the copper penny.
The
zinc went into the solution to form zinc ions and left the zinc plate
negative. The hydrogen ions of the sodium hydrogen sulphate were
attracted to the copper penny, where they lost their charges and became
gaseous hydrogen and formed gas bubbles on the penny. Therefore,
an electrical current was set up in the solution in
which the
strip of zinc became the negative electrode and the copper penny the
positive electrode.
EXPERIMENT 635 - Formation of a current by contact of silver with zinc
Using
the same solution and zinc strip as in the preceding experiment, see if
you can produce a current by means of a clean silver coin. Notice
that in this case bubbles of gas are also formed on the silver coin,
thereby setting up an electric current between the zinc and
silver. The explanation is the same as in the preceding
experiment.
ELECTROLYSIS
By
electrolysis is meant the decomposition or breaking down of a chemical
compound to form new substances by the aid of the electric
current. Many important commercial industries depend upon this
process for making and isolating different substances. For
example, some metals like aluminum are prepared on a large scale by
passing an electric current through a molten bath of certain
aluminum compounds. Again, sodium hydroxide (caustic soda) and
chlorine gas, used to a large degree in
GILBERT CHEMISTRY 195
making bleaching powder, are made by passing an electric current through a solution of sodium chloride.
In
the electrolysis of a solution of a chemical compound the positive ion
of the compound is always attracted to the negative pole where it loses
its charge and becomes an atomic substance. In this state it
reacts with the water present to form a new compound and usually a gas,
or is deposited on the negative pole as a metal.
The
negative ion, on the other hand, is attracted to the positive pole
where it loses its charge and becomes atomic in nature. In this
form it goes off as a gas or reacts with the water present to form a
new compound and a gas.
EXPERIEMENT 636 - The electrolysis of sodium chloride
Dissolve
one teaspoonful of common table salt (sodium chloride) in a tumbler
one-third full of water and add two or three drops of phenolphthalein
solution. Stir the solution a few times.
Now
connect two or three dry cells in series and place the ends of the
negative and positive wires in this solution about one~half inch
apart. Do not let the wires touch. Notice that almost
immediately bubbles of gas are formed at each wire in the
solution. At the positive wire chlorine gas is formed, while at
the negative wire hydrogen is formed. Notice also that the
solution turns red, showing that a base of alkali is being
formed. What really happened may be expressed a little more
clearly as follows:
Negative wire
Positive wire | Sodium
Chlorine gas | water = sodium hydroxide | hydrogen. |
EXPERIMENT 637 - The lemon electric cell
Procure a fresh, juicy lemon and cut two small slits, one on each side, as shown in the illustration.
Now
clean the copper and zinc plates by scrubbing them. Insert the zinc and
copper strips in the lemon as shown in the illustration. (Figure 46.)
To prove the passage of an electric current, touch your tongue to the
ends of the zinc and copper strips. Notice the slightly tingling
sensation produced on the tongue. This proves that a current is
passing from one metal to the other. When the extemal circuit is
closed, the citric acid (lemon juice) attacks the zinc, forming citrate
of zinc. By the separation of positive zinc from the zinc strip,
the zinc strip is made negative.
The positively charged
hydrogen ions of the citric acid, which is in the lemon, being
displaced by the zinc, deliver their positive charge to the
copper. Thus the copper is positively, and the zinc negatively,
charged when the copper is joined to the zinc or when the circuit is
closed. The flow of electricity externally is from the copper to
the zinc.
The lemon cell polarizes quickly; so lift out the plates frequently to remove the hydrogen bubbles.
EXPERIMENT 638 - How to clean silverware electrolytically
If
you have any silverware which is stained dark by exposure to the air
you can easily remove this stain, which is silver sulphide, by treating
the silverware as follows:
0btain an old aluminum pan and
place the silver to be cleaned in the pan. Now cover the silver
with a solution of common salt or baking soda made by dissolving two
spoonfuls of the salt in each quart of water used. Now place the
pan on the stove and
196 GILBERT CHEMISTRY
allow
the solution to boil for two minutes. Remove the silverware and
wash it with fresh water. Notice that the black stains are
removed and the silver is bright and clean.
The black
stain or silver sulphide was reduced by the chemical action taking
place in the solution. A feeble electric current was formed in which
the aluminum pan acted as the negative pole and the silverware as the
positive pole. The electrolyte in this case was the solution of common
salt or baking soda.
The metal silver cleaners which you
probably have seen advertised on the market are simply metals of
aluminum or zinc. The process of cleaning silverware with these
cleaners is the same as that used in this experiment.
EXPERIMENT 639 - How to galvanize iron with zinc
Mix
together on a sheet of paper four measures of powdered zinc, one
measure of aluminum sulphate, one-half measure of powdered magnesium
and three measures of calcium carbonate.
Now take a wet
cloth and after touching it to the mixture rub the clean iron to be
galvanized with some of the mixture. After thoroughly rubbing,
wash the iron free of the paste with water and notice that it is coated
with zinc.
Galvanized ironware is iron which has been treated with zinc compounds in a similar manner.
EXPERIMENT 640 - How to galvanize iron with nickel
Mix
together on a piece of paper three measures of calcium carbonate,
one-half measure of powdered magnesium and five measures of nickel
ammonium sulphate.
Now rub thoroughly by means of a wet
cloth some of this mixture on the clean iron to be galvanized.
Then wash off the paste with a little water and notice that the iron is
now plated with nickel.
[197]
LIST OF CHEMICALS WITH THEIR FORMULA
| 1 - Aluminum Sulphate | Al2(SO4)3 | .10 |
| 2 - Ammonium Chloride | NH4Cl | .10 |
| 3 - Ammonium Nitrate | NH4NO3 | .10 |
| 4 - Borax | Na2B4O7.10H2O | .10 |
| 5 - Boric Acid | H3BO3 | .10 |
| 6 - Litmus Paper | | .05 |
| 7 - Calcium Hypochlorite | CaOCl2 | .10 |
| 8 - Calcium Chloride | CaCl2.6H20 | .10 |
| 9 - Calcium Carbonate | CaCO3 | .10 |
| 10 - Camphor Gum | C20H16O | .10 |
| 11 - Calcium Oxide | CaO | .10 |
| 12 - Calcium Monophosphate | Ca(H2PO4)2H2O | .10 |
| 13 -Calcium Sulphate | CaSO4.2H20 | .10 |
| 14 - Calcium Sulphide Paper
|
| .10 |
| 15 - Carbon Tetrachloride | CCl4 | .10 |
| 16 - Cobalt Chloride
| CoCl2.6H2O | .10 |
| 17 - Cochineal
| | .10 |
| 18 - Congo Red Paper
| | .05 |
| 19 - Copper Strip
| Cu | .05 |
| 20 - Copper Sulphate
| CuS04.5H2O | .10 |
| 21 - Ferrous Ammonium Sulphute
| (NH4)2SO4.FeSO4.6H2O | .10 |
| 22 - Ferric Ammonium Sulphate
| (NH4)2SO4.Fe2(SO4)2.24H2O | .10 |
| 23 - Gum Arabic
| | .10 |
| 24 - Glycerine
| CH2OHCHOHCH2OH | .15 |
| 26 - Nickel-Steel Wire
| | .10 |
| 27 - Insulated Copper Wire
| | .10 |
| 28 - Logwood | | .10 |
| 29 - Magnesium Sulphate | MgSO4.7H2O | .10 |
| 30 - Manganese Dioxide
| MnO2 | .10 |
| 31 - Manganese Sulphate
| MnSO4.4H20 | .10 |
| 32 - Nickel Ammonium Sulphate
| (NH4)2SO4.NiSO4.6H2O | .15 |
| 33 - Phenolphhalein
| (C6H4OH)2COC6H4CO | .20 |
| 34 - Potassium Nitrate
| KNO3 | .15 |
| 35 - Potassium Permanganate
| KMnO4 | .10 |
| 36 - Powdered Iron Sulphide
| FeS | .10 |
| 37 - Powdered Charcoal
| C | .10 |
| 38 - powdered Iron
| Fe | .10 |
| 39 - Powdered Magnesium
| Mg | .15 |
| 40 - Powdered Zinc
| Zn | .10 |
| 42 - Sodium Bicarbonate
| NaHCO3 | .10 |
| 43 - Sodium Bisulphate
| NaHSO4 | .20 |
| 44 - Sodium Bisulphite | NaHSO3 | .15 |
| 45 - Sodium Carbonate
| Na2C03 | .10 |
| 46 - Sodium Ferrocyanide
| Na4Fe(CN)6.12H2O | .10 |
| 47 - Sodium Iodide Solution
| NaI | .10 |
| 48 - Sodium Silicate
| Na4SiO4 | .10 |
| 49 - Sodium Sulphocyanate | NaCNS | .15 |
| 50 - Sodium Thiosulphate
| Na2S2O3.5H2O | .10 |
| 51 - Strontium Nitrate
| Sr(N03)2 | .10 |
| 52 - Sulphide Test Paper
| | .10 |
| 53 - Sulphur
| S | .10 |
| 54 - Tannic Acid
| C14H10O9 | .20 |
| 55 - Tartaric Acid
| COOH(CHOH)2COOH | .20 |
[198]
| 56 - Turmeric Paper | | .05 |
| 57 - Zinc Strip | | .15 |
| 59 - Nigrosine | | .10 |
| 61 - Red Saunders | | .05 |
| 63 - Gum Benzoin
| | .15 |
| 64 - Collodion
| | .10 |
| 65 - Acetic Acid
| CH3COOH | .10 |
| 68 - Denatured Alcohol
| C2H5OH | .05 |
| 69 - Ammonia
| NH4OH | .05 |
| 73 - Strontium Chloride
| SrCl2.6H2O | .10 |
| 74 - Acetone | (CH3)2CO | .10 |
| 75 - Chrome Alum
| Cr2(S04)3.K2S04.24H2O | .10 |
Minerals
| X1500-A | Galena | .10 |
| X1500-B | Stibnite | .10 |
| X1500-C | Chalcopyrite | .15 |
| X1500-D | Pyrite | .10 |
| X1500-E | Magnetite | .10 |
| X1500-F | Pyrolusite | .10 |
| X1500-G | Sphalerite | .10 |
| X1500-H | Malachite | .10 |
| X1500-I | Calcite | .10 |
| X1500-J | Fluorite | .05 |
| X1500-K | Halite | .10 |
| X1500-L | Orthoclase | .05 |
| X1500-M | Talc | .10 |
| X1500-N | Apatite | .10 |
| X1500-O | Muscovite | .10 |
| X1500-P | Garnet | .05 |
| X1500-Q | Quartz | .10 |
APPARATUS AND EQUIPMENT
| X861-B | Wand | .05 |
| X1547 | Thermometer | .15 |
| X1551 | Test Tube Rack - Large | .25 |
| X1555-A | Scale - Complete | .50 |
| X1557 | Test Tube Rack - Medium | .20 |
| X1570 | Test Tube Rack - Small | .15 |
| *X1584 | Gas Generatmg Bottle - Glass | .10 |
| X1584-A | Alcohol Lamp | .20 |
| X2085 | Metal Alcohol Lamp | .15 |
| X3327 | Tank | .30 |
| P-57-A | Rod | .02 |
| P859 | Ring for Ink Trick | .05 |
| P860 | Black Cloth for Ink Trick | .05 |
| P1502 | 4" Test Tubes | .05 |
| P1503 | Glass Rod | .05 |
| *P1504 | Glass Tubes 4 1/2 | .05 |
| P1518 | Spoon | .05 |
| P1522 | Filter Paper Disc | 6 for .05 |
| P1556 | Test Tube Brush | .10 |
| P1548 | Flask | .50 |
[199]
| P1544 | Self Generating Torch with Swab and Cleaning Wire | .75 |
| P1549 | Beaker | .50 |
| *P1560 | Right Angle Tube-Long | .05 |
| P1563 | Test Tube Holder | .10 |
| P1574 | Charcoal Block | .20 |
| P1577 | Short Right Angle Tube | .05 |
| *P1578 | Glass Funnel | .15 |
| P1580 | Small Shovel | .02 |
| P1582 | Metal Test Tube Rack | .10 |
| P1583 | Carbon Electrodes | .10 |
| P1589 | Porcelain Pestle | .15 |
| P1593 | Glass Mortar | .10 |
| P1598-A | Cork with Hole | 2 for .05 |
| P1599 | Candle | .03 |
| *P3308 | Rubber Coupling | .01 |
| P3309-A | Rubber Tubing 2 ft | .35 |
| *P3310 | No. 2 Rubber Stopper - 2 holes | .05 |
| P3311 | No. 1 Solid Rubber Stopper | .10 |
| P3312 | No. 1 One Hole Rubber Stopper | .05 |
| P3313 | No. 0 Two Hole Rubber Stopper | .10 |
| P3314 | No. 0 One Hole Rubber Stopper | .05 |
| P3328 | Cork-No. 5 Standard Taper | .05 |
| P4727 | Horseshoe Magnet | .10 |
| P5607 | Glass Blowers Pipe | .25 |
| P8704 | Quill Brush | .03 |
| M1706 | Small Chemical ManuaL | .25 |
| M1710 | Large Chemical Manual | .35 |
| M1735 | Medium Chemical ManuaL | .35 |
| Chemical Magic Manual | .25 |
| Mineralogy Manual | .25 |
| Glass Blowing Manual | .25 |
The
parts marked * are necessary to make the Gas Generating Apparatus.
Kindly enclose check, money-order or stamps with your order.
THE A. C. GILBERT COMPANY
New Haven, Conn.
[Back Cover]
"The
Science Notebook" Copyright 2008-2012 - Norman Young
