The Science Notebook
Gilbert Chemistry - Part 10

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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  In addition, much of the information contained in this book about chemistry and other subjects is outdated and inaccurate.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 thiourea 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 thiourea.  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 sodium 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.  If 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 objections.  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 brilliance 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 chemical 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 from 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 potassium.  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 pole 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 object 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 object 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.  When 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 paraffin. 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. It 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 through 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 external 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 C20H16 .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  MnSO4.4H2 .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   NaHCO .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 Generating 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]



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"The Science Notebook"  Copyright 2008-2017 - Norman Young