The Science Notebook
Gilbert Chemistry - Part 5

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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  In addition, much of the information contained in this book about chemistry and other subjects is outdated and inaccurate.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 81- 100
GILBERT CHEMISTRY 81

EXPERIMENT 134 - How to test for soluble sulphates in water
Add two measures of strontium nitrate to a test tube one-third full of water and shake until dissolved. If after 10 or 20 minutes the water takes on a cloudy appearance, there are soluble sulphates present in the water.

EXPERIMENT 135 - How to test for lime in water
Add one or two measures of sodium carbonate to a test tube one-half full of the water to be tested and allow to stand for 10 or 20 minutes. If the water becomes cloudy or turbid, lime is present.

EXPERIMENT 136 - How to test for iron in water
Add one measure of sodium ferrocyanide to a test tube one-half full of water to be tested and shake until all is dissolved. A blue precipitate or blue color which may form at once or after standing for several minutes indicates the presence of iron in the water.

EXPERIMENT 137 - How to test for carbon doxide in water
Add a few drops of clear lime water to a test tube three-quarters full of water to be tested.  A white precipitate or a milky color is a test for carbon dioxide.

Lime water is made by adding one measure of calcium oxide to a test tube one-half full of water, shaking well and allowing any solid material to settle.  The clear liquid is lime water.  Common soda water such as is served at a soda fountain is simply pure water which has been saturated under pressure with carbon dioxide. When the pressure is relieved from such water the carbon dioxide bubbles out, producing what is known as effervescence.

SULPHUR

Sulphur is a very important element commercially, and plays a very significant part in the physiological processes of animal life.  It is a yellowish, tasteless solid and is practically odorless.  The odor commonly ascribed to sulphur is not that of sulphur itself, but is due to sulphur dioxide when sulphur undergoes oxidation.  The odor of burning sulphur is due to sulphur dioxide.

In the free state sulphur occurs chiefly in volcanic regions.  Large deposits are found in Italy, Sicily, China, Ireland and India.  Important deposits are found in this country in Louisiana and California.  In Louisiana the sulphur is melted under ground by means of superheated steam and forced out under pressure through pipes.  Sulphur also occurs in many important ores as sulphides, for example, galena or lead sulphide; cinnabar or mercury sulphide; zinc blende or zinc sulphide; realgar or arsenic sulphide, and in pyrite (iron sulphide).

Sulphur is used extensively in the commercial manufacture of many substances, such as gunpowder, fireworks, matches, dyestuffs, medicinal products, or drugs and fertilizers.  Without doubt the most important chemical containing sulphur, which is manufactured, is sulphuric acid.  It occupies a key position in chemical industry, and is utilized in hundreds of manufacturing operations.  Sulphuric acid is consumed in enormous quantities in the commercial processes applied in the vulcanization of rubber, in the bleaching industry, and in the manufacture of disinfectants and insecticides.  The great demand for insecticides by growers of fruit and truck garden products has led to the study of many materials to be used for plant protection.  Today this represents an enormous industry and there is a constant search for effective chemical insecticides.  Sulphuric acid is a valuable intermediate in their manufacture.
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EXPERIMENT 138 - Behavior of sulphur at different temperatures
Heat 10 measures of sulphur in a small, dry test tube. Apply the heat very slowly and notice the different changes. First, the sulphur melts to a light straw colored liquid.  Pour a little of this liquid into a glass of water, and then continue the heating of the tube, and observe, second, the change of color to brownish black and the liquids becoming almost solid. On further heating, third, this solid becomes liquid again. Pour this liquid sulphur into another glass of water.

The sulphur obtained when the straw colored liquid was poured into water is called rhombic sulphur, while that formed when the dark black liquid was poured into water is called plastic sulphur or elastic sulphur. This substance becomes brittle on standing for a few days. Sulphur undergoes three distinct changes then in heating and each change corresponds to a certain temperature.

EXPERIMENT 139 - Preparation of lime-sulphur solution
Put into a test tube one-third full of water one measure of calcium oxide and one measure of sulphur.  Heat the test tube over a flame and boil for several minutes.  Notice the yellow colored solution that is formed.  This solution is known as lime sulphur solution and is used on a large scale for spraying fruit trees and destroying fungi.

The calcium oxide reacted with the sulphur to form calcium sulphide, which is soluble in the water.  Filter a part of the calcium sulphide solution, and to the clear fluid add acetic acid until the solution is acid to litmus paper.  There will be an immediate evolution of hydrogen sulphide, which is evidenced by the odor.  Allow 1 or 2 drops of the calcium sulphide solution to fall on a polished silver coin, and let stand for a few minutes.  Then wash the coin with water and notice that a black spot of silver sulphide is formed.  Exposure of silverware to eggs will produce a similar discoloration due to the presence of sulphur in eggs.

EXPERIMENT 140-Sulphur dioxide from burning sulphur
Put 2 measures of sulphur in the spoon and heat over the flame.  The sulphur will suddenly take fire and burn with a blue flame.  The gas produced, having a suffocating odor, is sulphur dioxide, and is formed by the oxidation of sulphur when it burns in the air.

EXPERIMENT 141 - Sulphur dioxide from sodium bisulphite
Put two measures of sodium bisulphite in a test tube one-third full of water and add a few drops of acetic acid.  Smell cautiously at the mouth of the tube and notice the smell of burning sulphur.

Sodium bisulphite when treated with an acid reacts to form sulphur dioxide, water and a salt.

EXPERIMENT 142-Bleaching with sulphur dioxide



Put five measures of sodium bisulphite in a glass tumbler.
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Now obtain some colored flowers or pieces of dyed cloth and moisten them with water.  Put a teaspoonful of vinegar in the tumbler and quickly introduce the flowers or pieces of colored cloth. Place a saucer over the mouth of the tumbler and set aside for one-half hour. Figure 26.

Notice the vigorous reaction which takes place when the vinegar is added. This is due to the liberation of sulphur dioxide gas. At the end of a half hour examine the flowers or cloth and notice that some of the colors have been bleached out. Sulphur dioxide will bleach certain colors but not all colors.

Sulphur dioxide is used commercially in bleaching straw, silk and woolen goods, or any material that would be injured
by chlorine.

EXPERIMENT 143-Preparation of sulphurous acid



Put six measures of sodium bisulphite in the gas generator flask set up as shown in Figure 27 and add about one-half inch of water. Place over the end of the delivery tube a test tube one-half full of water so that the end of the delivery tube just extends below the surface of the water in the test tube.

Now add a little acetic acid, two or three drops at a time, through the funnel which must extend below the surface of the liquid in the generator flask. Notice the action which takes place. After passing the gas, which is formed in the reaction, into the test tube for several minutes, remove the test tube. Test the liquid in the test tube with blue litmus paper and notice that the litmus paper turns red, proving that an acid has been formed.  This acid is sulphurous acid.

The acetic ac1d reacted with the sodium bisulphite to form sulphur dioxide gas.  This gas when passed into the test tube of water reacted with the water to form suphurous acid.

We have shown that when sulphur is burned in the air or when sodium bisulphite is treated with an acid sulphur dioxide is formed.  Now in the presence of an oxidizing agent sulphur dioxide can be made to combine with one more atom of oxygen to form sulphur trioxide.

EXPERIMENT 144 - Preparation of sulphur trioxide.
Put three measures of sodium bisulphite and two measures of potassium permanganate in a clean, dry test tube and shake the tube until the two substances are thoroughly mixed.  Now insert the gas delivery tube and put the end of the delivery tube just below the surface of the water in another test tube one-third full of water.  Figure 28.
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Now heat slowly the test tube containing the mixture of the two compounds, being careful that the water in the second test tube does not suck back into the first test tube.  To prevent this remove the delivery tube from the tube containing the water when you stop heating. After passing the gas into the water for a few moments remove the test tube containing the water and and test the water with a piece of blue litmus paper. Notice that it turns red, proving that an acid is formed. This acid is sulphuric acid. Add a few drops of a solution of barium salt and note the result. Explain.

Sodium bisulphite when heated in the presence of an oxidizing agent like potassium permanganate forms sulphur dioxide, which is readily oxidized to sulphur trioxide. This oxide when passed into water forms sulphuric acid.

Sulphuric acid is really a very important acid. The reactions involved in the manufacture of this acid are more complicated than those of the manufacture of the other acids because it must be built up from its elements. Sulphuric acid is made commercially by either one of two methods.

First, the "Lead Chamber Process" or the older method.  In this process sulphur dioxide is prepared by burning sulphur or an ore of sulphur such as iron sulphide or pyrite. The sulphur dioxide is then conducted into large lead chambers where it comes in contact with oxygen, oxides of nitrogen and steam.  These react to form sulphuric acid which is concentrated by heat treatment.

The second method, known as the "Contact Process" is the more recent method and gives an acid of much higher purity.  This is a more expensive method, but this is compensated for by the degree of purity in the acid produced.  In this process sulphur dioxide is formed the same as in the lead chamber process.  It is then passed through a tube heated to 400 degrees Centigrade and containing a substance known as a catalytic agent.  The catalytic agent has the property of making the sulphur dioxide combine with more oxygen to form sulphur trioxide and this is passed into water forming concentrated sulphuric acid.

EXPERIMENT 145-Preparation of sulphuric acid
Mix together on a piece of paper 1/2 measure of sulphur and 1/2 measure of potassium nitrate.  Put 1/4 of this' mixture - no more - in a clean, dry test tube and heat slowly over a flame. Notice the white fumes which are given off. These fumes are sulphur trioxide. After the fumes stop coming off, stop the heating and place the thumb over the mouth of the tube.

After the tube has become cold, fill the test tube 1/2 full of water and shake the test tube, holding the thumb over the mouth. Test the liquid with blue litmus paper and notice that it turns red. Sulphur trioxide combined with the water to form  sulphuric acid.
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EXPERIMENT 146-Sulphuric acid from sulphur dioxide and hydrogen peroxide
Fit up your gas generator bottle as previously directed, but fill the test tube half full of hydrogen peroxide solution (dioxygen). Now generate sulphur dioxide by adding a little acetic acid, two or three drops at a time, through the funnel in the generator flask and pass the gas over into the hydrogen peroxide solution for three or four minutes.

Now remove the test tube from the delivery tube and test the solution with a piece of blue litmus paper. Notice that it turns red, proving that an acid was formed. This acid is sulphuric acid.

Sulphur dioxide was formed by the action of acetic acid upon sodium bisulphite, and sulphur dioxide when passed into hydrogen peroxide solution is oxidized to sulphur trioxide.  Sulphur trioxide reacted with water in the hydrogen peroxide solution to form sulphuric acid.

Sulphates are salts of sulphuric acid, and many of them find use in commerce. These salts are all soluble in water except those of barium, strontium and lead. The chemist makes use of this insolubility of their sulphates in precipitating these metals from their solutions.

EXPERIMENT 147 - How to make strontium sulphate
Dissolve one measure of aluminum sulphate in a test tube one-quarter full of water.  In another test tube one-quarter full of water dissolve two measures of strontium nitrate.  Now mix the two solutions and notice the white precipitate of strontium sulphate  which is formed.

Aluminum sulphate reacts with strontium nitrate to form a soluble compound of aluminum nitrate and an insoluble compound of strontium sulphate.

HYDROGEN SULPHIDE

Hydrogen sulphide (H2S) and water (H2O) are members of the same chemical family.  Water is a neutral substance, while hydrogen sulphide is a weak acid. The salts of hydrogen sulphide are called sulphides. Some sulphides are very insoluble in water and for that reason find application by chemists in analytical work. Certain metals can be separated from each other by means of their sulphides.

EXPERIMENT 148-How to make hydrogen sulphide
Cut a piece of paraffin from a candle or a piece of paraffin wax about the size of a pea and put it in a test tube. Add 2 measures of sulphur, place a piece of moistened sulphide test paper over the mouth of the tube and heat the tube slowly. Notice that the test paper turns black This is a test for hydrogen sulphide gas.  The test paper contains lead acetate and when the hydrogen sulphide comes in contact with it, it forms a black precipitate of lead sulphide.

Remove the tube from the flame and smell cautiously at the mouth of the tube. Note the resemblance of the odor to that of rotten eggs. As a matter of fact this is the gas produced when eggs go bad. Hydrogen sulphide is given off from several organic compounds, for example, when cabbage is cooked.

Hydrogen sulphide is inflammable and when burned the hydrogen combines with oxygen to form water while the sulphur combines with oxygen to form sulphur dioxide.

EXPERIMENT  149 - Action of hydrogen sulphide on sulphur dioxide
Prepare hydrogen sulphide gas as in preceding experiment, using five measures of sulphur instead of two measures.
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Now pass this gas by means of a delivery tube into a test tube containing two measures of sodium bisulphite and six or eight drops of vinegar or acetic acid. (Figure 29.)  Notice that a deposit of sulphur is formed around the inside of the test tube containing the sodium bisulphite and vinegar. 

Sulphur dioxide was formed in the second test tube by the action of the vinegar or sodium bisulphite and vinegar. This reacted with the hydrogen sulphide gas to form su1phur and water.  This is the way sulphur is formed around many volcanic regions.

EXPERIMENT 150 - Action of chlorine gas on hydrogen sulphide
Prepare a solution of hydrogen sulphide water by bubbling hydrogen sulphide gas into water.

Now prepare some chlorine gas by putting five measures of tartaric acid and three measures of calcium hypochlorite in a test tube one-quarter full of water.  Attach the gas delivery tube to this test tube and allow the gas which comes off to bubble through the hydrogen sulphide water prepared above. Notice that a white precipitate is formed. This is sulphur.

Chlorine reacts with hydrogen sulphide to form hydrochloric acid and sulphur.

EXPERIMENT 151 - Reducing action of hydrogen sulphide
Dissolve a crystal of potassium permanganate in a test tube half full of water.

Now bubble hydrogen sulphide gas, prepared as described in a previous experiment, using a gas delivery tube, into the solution of potassium permanganate  and notice that the purple color fades and a white precipitate of sulphur is formed. 

Hydrogen sulphide gas reduced the potassium permanganate, therefore removing its color.  In reducing the permanganate it is oxidized by oxygen in the permanganate to water and sulphur.  Hydrogen sulphide gas is often used as a reducing agent, and the two preceding experiments with chlorine and hydrogen peroxide illustrate this behavior

You probably have noticed that some white paints turn black after exposure for a long time.  This is because such paints contain lead, chiefly in the form of the pigment lead carbonate. The lead reacts with traces of hydrogen sulphide gas in the air to form black lead sulphide.  To prevent this discoloration, zinc oxide is used as a base pigment in place of lead carbonate. When zinc oxide reacts with hydrogen sulphide a white precipitate of zinc sulphide is formed.

EXPERIMENT 152-How to restore the color of white paint
Obtain some white oil paintings which have become dark by the action of hydrogen sulphide. Wash these paintings with a little hydrogen peroxide solution and  notice that they become white again. 
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EXPERIMENT 153 - Silver sulphide
Place 1/2 measure of sulphur on a bright silver coin and wrap in several thicknesses of paper.  After a few days you will find a black spot of silver sulphide on the coin where the sulphur was in contact with it.

EXPERIMENT 154 - Sulphur in rubber
Rubber contains sulphur used in its vulcanization.  Wrap a rubber band around a silver coin and you will find that it will turn black after a few days, due to the formation of silver sulphide.

EXPERIMENT 155 - Sulphur and silver coin
a silver coin is turned black in a few hours by a paste of mustard and water, as mustard contains sulphur.  Eggs also contain sulphur, and this is the reason why silver spoons turn black when used for eating eggs.

EXPERIMENT 156 - Nickel sulphide
Dissolve one measure of nickel ammonium sulphate in a test tube one-quarter full of water.  Fill another test tube one-quarter full of water and add four measures of sodium bisulphate. Shake to dissolve the sodium bisulphate and add two measures of iron sulphide.  You will find this in any drug store.  Fit the test tube with the gas delivery tube and stopper and when hydrogen sulphide gas is coming off freely, allow it to bubble through the nickel ammonium solution.  ln a few minutes you will notice a black precipitate of nickel sulphide forming in the nickel ammonium sulphur solution.

EXPERIMENT 157 - Copper sulphide
Place one measure of copper sulphate in a test tube and fill the tube half full of water, warm the mixture gently until the solid is dissolved.  Now cool the solution and pass in hydrogen sulphide gas through the gas delivery tube as in the preceding experiment.  A black precipitate of copper sulphide will be formed.

  EXPERIMENT158 - Zinc sulphide
Place 2 measures of sodium bisulphate and a small piece of zinc metal in a test tube and fill the tube 1/4 full of water. Heat the tube gently and wait until some of the zinc has dissolved. Now pour some of the clear solution into another test tube, add water to fill the tube one-half full and pass in hydrogen sulphide gas.

EXPERIMENT 159 - Ferrous sulphide from sodium thiosulphate
Dissolve one measure of ferrous ammonium sulphate in a test tube one-quarter full of water.  Add one measure of sodium thiosulphate and heat the solution for a minute or two.  A greenish brown precipitate of ferrous sulphide will form.

EXPERIMENT 160 - Ferric sulphide from sodium thiosulphate
Add one measure of ferric ammonium sulphate in a test tube one-quarter full of water.  Add one measure of sodium thiosulphate and heat the solution. This time a brown precipitate will form.

EXPERIMENT 161 - Nickel sulphide from sodium thiosulphate
Dissolve one measure of nickel ammonium sulphate in a test tube one-quarter full pf water.  It may be necessary to warm the tube slightly to completely dissolve the nickel ammonium sulphate. Now add one measure of sodium thiosulphate and the black precipitate, consisting of nickel sulphide, will be formed as soon as the solution is heated.
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EXPERIMENT 162-Manganese sulphide from sodium thiosulphate
To form a white precipitate of manganese sulphide, dissolve one measure of manganese sulphate in a test tube one-quarter full of water. Add one measure of sodium thiosulphate; warm the solution gently and the white precipitate will form.

THE HALOGENS

The elements that go to make up the halogen family are fluorine, chlorine, bromine and iodine. These elements are called halogens, meaning salt producers. They all resemble each other very much in chemical properties but differ widely in physical properties. Fluorine is a colorless gas, chlorine a greenish yellow gas, bromine a brownish-red liquid and iodine a purple black solid.

The halogens are very active substances, so that they never occur in the free state in nature. Their compounds are very abundant - those of chlorine, bromine and iodine occurring in sea water.  The most common of these is sodium chloride or common salt.

As already stated, the halogens are very active substances.  They combine with metals like copper, sodium, potassium, gold, silver, platinum, etc., to form salts of these metals.  They also react with non-metals like sulphur, antimony and arsenic to form compounds with these substances.  They also react with hydrogen to form the corresponding acids, namely, hydrofluoric, hydrochloric, hydrobromic and hydriodic acids.  Of the halogens, fluorine is the most active and iodine the least active.  All four of the halogens find wide commercial applications.

Chlorine is used extensively as a bleaching agent and germicide. Chlorine gas is shipped in bulk compressed in iron cylinders. The gas is widely used for water purification.  It also comes on the market known as bleaching powder or chloride of lime.  The corresponding acid, hydrochloric acid, is an important technical acid and is used for a number of purposes.

Bromine is used principally in the preparation of bromides, which are used to a considerable extent in photography and in medicine.  lt is also used in the preparation of a number of organic drugs and dyestuffs.  Bromine is extracted today in large quantities from sea water and apparently this source is inexhaustible.

The chief sources of iodine are brine wells and the ashes of certain sea weeds.  Iodine is used extensively in medicine, especially in the form of tincture of iodine.  It also finds an important use in the preparation of iodides and of certain dyes and drugs.  The antiseptic iodoform is a compound of iodine with carbon and hydrogen.  This iodine compound is analogous to the widely used anesthetic - chloroform - which is a compound of chlorine combined with hydrogen and carbon. While iodoform and chloroform are valuable drugs, the corresponding compounds of bromine and fluorine are unimportant compounds in medicine.

EXPERIMENT 163 - How to make chlorine gas
Put two measures of potassium nitrate, two measures of sodium bisulphate and two measures of sodium chloride (common table salt) in a test tube and heat the test tube gently over a flame for a few moments.  Remove the test tube from the flame and smell cautiously the gas which is given off.  This is chlorine gas. 

Sodium bisulphate reacted with sodium chloride to form hydrogen chloride gas which was oxidized by oxygen from the potassium nitrate to water and chlorine gas. 

EXPERIMENT 164 - To show the bleaching properties of chlorine
Prepare chlorine gas as in the preceding experiment, placing a small piece of moistened blue litmnus paper over the mouth of the tube before heating. Notice on   
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heating that the blue litmus paper turns white, showing that chlorine gas has the property of bleaching certain colors. 

What happened was that the chlorine gas reacted with the water on the blue litmus paper forming hydrochloric acid and oxygen. It is really this free oxygen that does the bleaching.

EXPERIMENT 165 - How to make hydrochloric acid
Put two measures of ammonium chloride and two measures of sodium bisulphate in a test tube.   Moisten a piece of blue litmus paper and place it over the mouth of the test tube.  Now heat the tube slowly over a flame for a few minutes.  Notice that the litmus paper turns red, proving that an acid has been formed. Remove the test tube from the flame and smell cautiously the gas that is given off.  This is hydrogen chloride gas.

Dip the glass stirring rod in a little household ammonia and hold the rod over the mouth of the test tube.  Notice the white fumes that are formed.  These fumes are ammonium chloride fumes.

Hydrogen chloride gas, as prepared in this experiment, when dissolved in water forms hydrochloric or muriatic acid.   Commercially, hydrochloric acid is manufactured by heating sodium chloride with sulphur acid.

BLEACHING POWDER

Bleaching powder or "Chloride of Lime," as it commonly comes on the market, is a compound composed of calcium, oxygen and chlorine. It is prepared by passing chlorine gas over slaked lime, bleaching powder or calcium hypochlorite being formed. 

Bleaching powder is a very important compound and has many uses in everyday life.  It is a very good bleaching agent and readily gives up its chlorine when treated with an acid.  In bleaching paper rags, the rags are first boiled in an alkali to remove the grease, then placed in a large vat with bleaching powder and sulphuric acid; on removing, the rags are pure white.  Cotton cloth is bleached by passing it through alternate vats of bleaching powder and sulphuric acid.

Besides being used as a bleaching agent chloride of lime is employed as a disinfectant, since it destroys germs. Water is sometimes purified with this compound.

EXPERIMENT 166 - How to make chlorine from bleaching powder
Make a solution of tartaric acid in water by adding 3 measures of tartaric acid to a test tube containing about 1/2 inch of water. Then add 3 measures of calcium hypochlorite or bleaching powder and smell cautiously at the mouth of the tube.  Note the odor of chlorine gas. The other compound formed in the reaction is calcium tartrate.

EXPERIMENT 167 - Bleaching with bleaching powder
For this experiment obtain two or three pieces of colored cloth and some colored flowers; a red carnation works well.

Put 5 measures of calcium hypochloride (bleaching powder) and 5 measures of tartaric acid in a clean glass and add a few drops of water to moisten the compounds.  Then moisten the pieces of colored cloth and flowers with water, place them in the glass and cover the glass with a saucer.   Allow the glass to stand for an hour.  Notice that the cloth and the flowers lose their color, and become white, due to the bleaching effect of the chlorine gas liberated in the reaction.
 

EXPERIMENT - 168 How to make iodine
Put 4 drops of sodium iodide solution into a test tube 1/4 full of water and mix the contents of the tube by shaking.
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Now prepare chlorine gas as already shown in a previous experiment and fit the test tube with a gas delivery tube. Allow the chlorine gas to bubble through the sodium iodide solution prepared above and notice after a few moments that the solution turns brown.

Chlorine gas reacts with sodium iodide to form sodium chloride and free iodine.  It is this free iodine that gives the solution its brown color. 

Now add 6 or 8 drops of carbon tetrachloride to this solution containing the iodine, close the mouth of the tube with your thumb and shake several times.  Allow the test tube to stand for a few seconds and notice that the carbon tetrachloride has become red and the brown color has disappeared from the water.

EXPERIMENT 169 - How to test for iodine
Prepare some starch solution by putting 1 measure of powdered household starch in a test tube and moisten with a few drops of water.  Now heat a test tube half full of water to boiling and pour the hot water into the test tube containing the starch paste. To this starch solution add 5 drops of sodium iodide solution.

To a dry test tube add 2 measures of common table salt or sodium chloride, 2 measures of potassium nitrate and 2 measures of sodium bisulphate. Insert the perforated cork with gas delivery tube and heat the test tube slowly over a flame. After the  gas starts to come off freely insert the end of the delivery tube into the test tube containing the starch solution and sodium iodide and allow the chlorine gas to bubble through the starch solution for several moments.  Notice the blue color which is formed.  This is the test for free iodine.

The chlorine gas displaced the iodine in the sodium iodide solution, liberating iodine. Free iodine in the presence of starch produces a blue color.

EXPERIMENT 170 - Formation of lead iodide
Fill a test tube one-third full of water and add six drops of sodium iodide solution.  In another test tube place about one measure of lead nitrate or acetate obtainable at any drug store and dissolve by adding one-third test tube of water. Now pour the nitrate solution into the sodium iodide solution. A heavy bright yellow precipitate of lead iodide will form.  Now heat until it begins to boil, then set aside to cool.  On cooling watch closely what happens.  Most of the lead iodide will have settled to the bottom, but there also appears above it, numerous little scales or specks of all colors - some golden, some silver blue, green, red, pink, orange, and violet which sparkle beautifully. The lead iodide, which by this time has all settled to the bottom of the test tube, leaves the most beautiful colored specks in the almost clear liquid above it.  Its beauty cannot be very easily described, but soon the beautiful specks settle to the bottom of the test tube leaving only a few lingering above them. Even at the bottom they produce a striking effect. It is very interesting to watch the colored particles.

EXPERIMENT 171 - Partition solubility of iodine
To a half test tube of water add about ten drops of tincture of iodine (this you will find in the medicine closet). The solution in the test tube will be a reddish-brown color. Add to this an eighth test tube of carbon tetrachloride. The carbon will sink to the bottom. Shake the test tube and then let the carbon tetrachloride layer settle to the bottom of the tube.  The bottom layer will be a rich violet color.

Reaction: Tincture of iodine is a solution of iodine and potassium iodide in water and alcohol. When carbon tetrachloride is added, it dissolves the free iodine. The carbon tetrachloride settles to the bottom of the test tube because it is heavier than water and it is not miscible with water.
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EXPERIMENT 172 - Testing vegetables for starch
Make a solution of iodine by dissolving 2 crystals of iodine in a test tube 1/4 full of water containing 5 drops of sodium iodide solution. You will notice that the solution turns brown, showing that iodine is soluble in sodium iodide solution.

Now cut in half a potato, beet, carrot or any other vegetable that you may obtain and add 2 or 3 drops of the iodine solution to the freshly cut surface. Notice which of the vegetables produce a blue color. The potato contains a lot of starch. A more pronounced blue color may be obtained by boiling a small piece of the vegetable and adding 1 or 2 drops of the iodine solution to the cool solution containing the vegetable.

EXPERIMENT 173-Testing other substances for starch
Test some grains of corn, barley and wheat for starch the same way you did in the preceding experiment. Notice that these substances contain starch.

GAS WARFARE



It was not until the last World War that poisonous gases were demonstrated to be an important factor in modern military science. They were introduced so unexpectedly during the critical period of the world’s conflict that the unprepared combatants were handicapped in military efficiency, and months of intensive training in the new technique of chemical warfare became necessary before the different countries were able to provide a defense against this new method of attack. In the early development of this new method of warfare, chlorine gas or compounds con-
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taining this halogen were used extensively, and they made up the bulk of the so-called poisonous gases. Chlorine itself is a heavy suffocating gas which can be produced cheaply, and is easily transported in steel cylinders. Other chlorine compounds of high toxicity which were used in quantity as poisonous gases were chloropicrin and phosgene. Chlorine gas was later abandoned and was replaced by special compounds containing this element in combination with sulphur, carbon and hydrogen, which pr proved to be more destructive and efficient for offensive military movements. One of the most valuable products developed for the chemical warfare service was a chlorine compound known as "mustard gas." Large chemical plants were operated in the United States during the World War for the manufacture of chlorine gas, phosgene, chloropicrin, and mustard gas, to be shipped abroad to the military forces engaged in this destructive war.

Today poisonous gases fulfill an important commercial service in their uses as protective measures against bank robberies, and for police equipment in controlling public riots and serious labor strikes. Such cases provide a more effective and humane weapon of defense than the rifle or police gun.

THE GAS MASK

As a preventative from gas poisoning, the well-known gas mask was invented.  This consisted of a face piece to shut out the gases from the nose, mouth and eyes and from which ran a flexible rubber tube to a cannister or container which held the chemical for neutralizing the poisonous gases. On breathing in, the poisonous air passes into the cannister where the deadly gases are removed, allowing the good air to pass up through the flexible tube, the end of which is held in the mouth, and then into the lungs.  The exhaled air is passed out through a rubber slit in the lower part of the face piece. The chemicals used to remove the gases were principally a mixture charcoal and soda lime.

BORON AND THE BORATES

Boron does not occur as the free element. It has been found in nature in the form of boric acid in many hot springs, particularly in Italy and California. Boron occurs in large quantities in the desert regions of California and Nevada in the form of its sodium salt, known as borax, ordinary "Twenty Mule Team Borax." It also occurs as the calcium  salt.

Boric acid is used as a mild antiseptic, as a constituent of talcum powder, and as a preservative.

EXPERIMENT 174 - Boric acid from borax
In a test tube 1/4 full of water, dissolve 8 measures of borax heating the tube a little to completely dissolve the solid. In another test tube 1/4 full of water dissolve, by heating if necessary, S measures of sodium bisulphate. Now pour the sodium bisulphate into the borax solution and cool the resulting solution by holding the test tube in water. After some time a white solid crystallizes out. This solid is boric acid.

EXPERIMENT 175-Borax from boric acid
Put 2 measures of boric acid in a test tube 1/4 full of water and heat to boiling over a flame. Now add 3 measures of sodium carbonate and boil the solution for two or three minutes. Set the tube aside to cool and observe the behavior while crystals separate out. These are crystals of sodium tetraborate or borax.
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EXPERIMENT 176 - Test for boric acid
Dissolve 2 measures of boric acid in a test tube 1/3 full of alcohol. Now pour this solution into a saucer, darken the room and light the alcohol with a flame. Notice that the alcohol burns with a green flame. This is a test for boric acid.

EXPERIMENT 177 - Examination of talcum powder
Repeat experiment 176 using instead of the boric acid 3 or 4 measures of a talcum powder.  Some talcum powders contain boric acid.

BORAX GLASS

When heated, borax swells up to a bulky mass, loses its water of crystallization and then melts to a clear glass. This glass readily dissolves various metallic oxides which impart characteristic colors to the glass. This property is used in testing for certain metals.  For this same reason borax is used as a flux in brazing or hard soldering to remove the oxides from the surface of the metals to be joined.

EXPERIMENT 178 - Cobalt borax glass
Put 1 measure of borax on a clean sheet of paper and mix with it a very small quantity (a speck about the size of a pin point) of cobalt chloride. Now pick up some of this mixture on the loop of your nickel steel wire and heat it over the alcohol lamp flame.  The borax will melt as before, but you will find that the glass which is formed will be blue in color because of the cobalt which dissolved in it. If very much cobalt is used the film will appear to be black, so intense is the coloring power, but if only a very slight trace of the cobalt is used the film will be a beautiful azure blue color.

EXPERIMENT 179 - Iron borax glass
Take a fresh quantity of borax, about 1 measure, and put it on a clean sheet of paper.  Mix with the borax a very small trace of ferric ammonium sulphate.

Now put some of this mixture on the loop of your nickel steel wire and heat it.  This time you will obtain yellow borax glass due to the presence of iron.

EXPERIMENT 180 - Manganese borax glass
Manganese colors borax violet or lilac.  Mix a very small amount of manganese sulphate with 1 measure of borax and make a ball of borax glass on your nickel steel wire using this mixture.

EXPERIMENT 181 - Nickel borax glass
Nickel colors borax glass brown.  Mix a very small quantity of nickel ammonium sulphate with 1 measure of borax and make a ball of borax glass from this mixture.

EXPERIMENT 182 - Chromium borax glass
Chromium colors borax glass green. Mix a very small quantity of chrome alum with 1 measure of borax.  Make a ball of borax glass from this mixture.

BORON COMPOUNDS

EXPERIMENT 183 - Strontium borate
Dissolve 2 measures of strontium chloride in a test tube 1/2 full of water. In another test tube 1/4 full of water dissolve 2 measures of borax. Now pour one of these solutions into the  other and notice the heavy white precipitate of strontium borate which forms.
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EXPERIMENT 184 - Magnesium borate
Dissolve 2 measures of magnesium sulphate in a test tube 1/4 full of water. Upon pouring this into a solution of borax a white precipitate of magnesium borate is formed.

EXPERIMENT 185 - Aluminum borate
Prepare a solution of 2 measures of aluminum sulphate in a test tube 1/4 full of water, and add to this a solution of 2 measures of borax, dissolved in a test tube 1/4 full of water.

EXPERIMENT 186 - Ferric borate
Prepare a solution of 2 measures of ferric ammonium sulphate in a test tube 1/4 full of water, and also a solution of 2 measures of borax in a test tube 1/4 full of water.  Upon pouring one of these solutions into the other a heavy precipitate of ferric borate is formed.

EXPERIMENT 187 - Cobalt borate
Dissolve 1 measure of cobalt chloride in a test tube 1/4 full of water. In another test tube 1/4 full of water dissolve 2 measures of borax. Pour the cobalt solution into the borate solution and a very pretty precipitate of cobalt borate will result.

EXPERIMENT 188 - Nickel borate
To precipitate nickel borate prepare a solution of two measures of nickel ammonium sulphate in a test tube 1/4 full of water. lt is necessary to heat the solution a little in order to dissolve all of the nickel ammonium sulphate. In another test tube prepare a solution of two measures of borax and pour the nickel ammonium sulphate solution into the borate solution. A thick greenish precipitate of nickel borate will result.

EXPERIMENT 189 - Manganese borate
Dissolve 2 measures of manganese sulphate in a test tube 1/4 full of water, and dissolve 2 measures of borax in another test tube 1/4 full of water. Pour the manganese solution into the borate solution and a thick white precipitate of manganese borate will be formed.

EXPERIMENT 190 - Calcium borate
Prepare a solution of 2 measures of calcium chloride in a test tube 1/4 full of water.  In another test tube dissolve 2 measures of borax and pour the calcium chloride  solution into the borax solution.

EXPERIMENT 191 - Chromium borate
Prepare a solution of 2 measures of chrome alum in a test tube 1/4 full of water.  Dissolve 2 measures of borax in another test tube 1/4 full of water. Upon pouring these solutions together a green precipitate of chromium borate is formed.

PHOSPHOROUS AND THE PHOSPHATES

Phosphorus never occurs free in nature but is found is combination with oxygen and metals as derivatives of phosphoric acid. It occurs most extensively as calcium phosphate. All fertile soils contain calcium phosphate. Since it is essential to plant growth, it is an important constituent of fertilizers, the soluble calcium monophosphate being used. The bone of animals is largely calcium phosphate.

Phosphorus exists in two forms. Yellow phosphorus is a transparent, wax-like solid which often takes fire in air at ordinary temperature. It is always kept under water.
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Yellow phosphorus is very poisonous.  Red phosphorus is a chocolate red amorphous powder and is quite stable in air at ordinary temperature.

The phosphates of most metals can be precipitated from solution of the salts since most phosphates are insoluble in water.

EXPERIMENT 192 - Nickel phosphate
Place in a test tube 1/2 measure of sodium carbonate and 1/2 measure of calcium monophosphate.  Fill the test tube half full of water and shake for a moment. The heavy white precipitate which is formed will gradually settle to the bottom of the tube leaving a clear solution on top.  This solution contains sodium phosphate which is soluble in water and the precipitate in the bottom of the tube consists of calcium carbonate.

Now place in another test tube two measures of nickel ammonium sulphate. Fill the test tube half full of water and heat for a few moments to completely dissolve the solid.  Cool the solution of nickel ammonium sulphate by holding the bottom of the tube in cold water for a moment, and then add a few drops of the clear solution of sodium phosphate to the nickel ammonium sulphate solution. A thick green precipitate of nickel phosphate will be formed.

The precipitate of nickel phosphate is soluble in solutions containing ammonium salts.  Place 3 measures of ammonium chloride in a test tube. Fill the tube 1/4 full of water and shake to dissolve the ammonium chloride. Add to this solution about 1/4 of a test tube of the nickel phosphate precipitate and shake the tube vigorously.  Notice that the precipitate is dissolved in the ammonium chloride solution and a clear green liquid results.

Nickel phosphate is also soluble in acids. Prepare a solution of 3 measures of sodium bisulphate in a test tube 1/4 full of water and add to this solution 1/4 of a test tube of the nickel phosphate precipitate. Notice that the nickel phosphate is again dissolved in the solution, leaving a clear green liquid.

EXPERIMENT 193 - Copper phosphate
Prepare a solution of sodium phosphate by adding 1/2 measure of sodium carbonate and 1/2 measure of calcium monophosphate to a test tube half full of water.

Now prepare a solution of copper sulphate. Add to this copper sulphate solution a few drops of the sodium phosphate solution and a very pretty blue precipitate of copper sulphate will be formed.

EXPERIMENT 194-Strontium phosphate
Make a solution of sodium phosphate by dissolving sodium carbonate and calcium monophosphate in water.

Prepare a solution of 2 measures of strontium chloride in a test tube half full of water and add to this a few drops of the clear sodium phosphate solution. A thick white precipitate of strontium phosphate will be formed.

EXPERIMENT 195 - Aluminum phosphate
Prepare a solution of sodium phosphate as before and add a few drops of this to a solution of 2 measures of aluminum sulphate in 1/4 test tube of water.

EXPERIMENT 196-Ferric phosphate
Place 2 measures of ferric ammonium sulphate in a test tube half full of water and shake to dissolve the solid.  Now add to this solution a few drops of sodium phosphate solution and examine the brownish white precipitate of ferric phosphate.
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EXPERIMENT I97 - Manganese phosphate
Dissolve 2 measures of manganese sulphate in a test tube half full of water by heating.  Cool the solution and add a few drops of sodium phosphate as prepared before.  The white precipitate tinged with pink is manganese phosphate.

EXPERIMENT 198 - Calcium phosphate
Place 2 measures of calcium chloride in a test tube half full of water and shake vigorously for a minute or two.  Now add to this solution a few drops of sodium phosphate made as before. This white precipitate formed is calcium phosphate; the same substance chemically as phosphate rock.

EXPERIMENT 199-Cobalt phosphate
Dissolve 1 measure of cobalt chloride in a test tube half full of water and add a few drops of sodium phosphate solution.  A beautiful light blue precipitate of cobalt phosphate will appear in the test tube.

EXPERIMENT 200 - Magnesium phosphate
Dissolve 2 measures of manganese sulphate  [NOTE: This should probably be magnesium sulphate]  in a test tube half full of water.  To this solution add a few drops of sodium phosphate solution prepared as before.

EXPERIMENT 201 - Chromium phosphate
Dissolve 2 measures of chrome alum in a test tube 1/4 full of water. Fill a second clean test tube 1/4 full of sodium phosphate solution prepared as before.  Now add a few drops of chrome alum solution to the sodium phosphate solution and a light blue precipitate of chromium phosphate will form.

THE ALKALI METALS

The alkali metals are lithium, sodium, potassium and rubidium and they are all very similar in their chemical behavior. The two most common are sodium and potassium. These metals are called alkali metals because they are a part of the compounds which are known as alkalies or bases, such as caustic soda (sodium hydroxide) and caustic potash (potassium hydroxide). 

Because of their extreme reactivity none of these metals occur free in nature.  They are found as compounds distributed in sea and mineral water, salt beds and rocks.  The free metals are soft, with a silvery luster, but tarnish quickly in air because  of the reaction with oxygen. They are kept in kerosene out of contact with the air. They react vigorously with water, setting free hydrogen from the water.

Some of the more important compounds are sodium hydroxide, the chief constituent of ordinary lye; sodium chloride, or common salt; sodium carbonate, or washing soda; sodium bicarbonate, or baking soda.

EXPERIMENT 202 - How to make sodium hydroxide
Dissolve 2 measures of sodium carbonate in a test tube 1/2 full of water.  To this solution add 2 measures of calcium oxide and shake the tube. Heat cautiously over the flame for a few minutes to complete the reaction and filter the solution into another test tube. The calcium oxide reacted with the sodium carbonate to form sodium hydroxide and a white precipitate of calcium carbonate. The clear filtered solution contains the sodium hydroxide.

To a test tube full of water add 3 drops of phenolphthalein solution and and 2 drops of the sodium hydroxide solution prepared above. The red color proves that sodium hydroxide is a base. Save the sodium hydroxide for the following experiments.
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EXPERIMENT 203 - Manufacture of sodium bicarbonate or baking soda
Sodium bicarbonate is manufactured on a commercial scale by what is known as the Solvay process.  This consists essentially of treating a saturated solution of common salt in ammonium hydroxide with carbon dioxide gas. The carbon dioxide gas reacts with the ammonium hydroxide to form ammonium bicarbonate which in turn reacts with the sodium chloride to form sodium bicarbonate. This is insoluble in the ammonium chloride formed in the reaction and precipitates out.

Make a saturated solution of common salt by shaking a teaspoonful of common salt in a flask or bottle with about 3 spoonfuls of common household ammonia. Filter about a half inch of this strong solution into a test tube.

Now pass carbon dioxide into this strong solution for half an hour. Notice the precipitate which forms. This is sodium bicarbonate. The carbon dioxide is prepared by putting 3 spoonfuls of washing soda or baking soda in the generator bottle and adding enough  water so that the end of the funnel comes just below the surface of the water in the bottle. Now add small amounts, 2 or 3 drops at a time, of vinegar or a solution of tartaric acid to keep up the flow of gas.

EXPERIMENT 204 - To convert sodium bicarbonate into sodium carbonate
Put 1 measure of sodium bicarbonate into a test tube half full of water and add 2 drops, no more, of phenolphthalein solution. Notice the pink color which is produced.

Now heat the solution for several moments and notice that the pink color changes to red.  This is because sodium carbonate which is formed when sodium bicarbonate is heated has stronger basic properties than sodium bicarbonate. The gas liberated in the reaction is carbon dioxide gas.

The hydroxides of many metals are insoluble and are precipitated by addition of sodium hydroxide to a water solution of salt of these metals.

HYDROXIDES

EXPERIMENT 205 - Aluminum hydroxide
Dissolve 1 measure of aluminum sulphate in a test tube half full of water and add a few drops of the sodium hydroxide solution just prepared. A thick white precipitate of aluminum hydroxide is formed.

EXPERIMENT 206 - Ferric hydroxide
Dissolve 1 measure of ferric ammonium sulphate in a test tube half full of water and again add a few drops of the sodium hydroxide solution. A very pretty red-brown precipitate immediately forms which is iron hydroxide.  This material is similar to iron rust and is used in paints.

EXPERIMENT 207 - Nickel hydroxide
Dissolve 1 measure of nickel ammonium sulphate in a test tube half full of water, heating the solution a little if necessary, to make the solid all dissolve. Add a few drops of sodium hydroxide and a blue-green precipitate of nickel hydroxide is formed.

EXPERIMENT 208 - Manganese hydroxide
Place 1 measure of manganese sulphate in a test tube half full of water and shake well to dissolve the solid. Now add a few drops of sodium hydroxide solution and you will obtain a thick white precipitate of manganese hydroxide.
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EXPERIMENT 209 - Zinc hydroxide
Place a small piece of zinc and 1 measure of sodium bisulphate in a test tube half full of water. Warm this solution until the solids are all dissolved, and after it has cooled a little add a few drops of sodium hydroxide solution.

EXPERIMENT 210 - Cobalt hydroxide
Dissolve 1 measure of cobalt chloride in a test tube half full of water and add a few drops of sodium hydroxide solution. A very pretty blue precipitate of cobalt hydroxide is formed which very soon changes to red.

EXPERIMENT 211 - Magnesium hydroxide
Dissolve 2 measures of magnesium sulphate in a test tube half full of water.  Add a few drops of sodium hydroxide solution. A heavy white precipitate of magnesium hydroxide is formed.

EXPERIMENT 212 - Calcium hydroxide
Dissolve 2 measures of calcium chloride in a test tube half full of water. Now add a few drops of sodium hydroxide solution and a white precipitate of calcium hydroxide  will form. This calcium hydroxide is the same substance that is obtained when lime is slaked.

EXPERIMENT 213 - Chromium hydroxide
Dissolve 2 measures of chrome alum in a test tube 1/4 full of water. To this solution add a few drops of sodium hydroxide solution. A beautiful green precipitate of chromium hydroxide is formed.

Potash or potassium carbonate is an important compound and is essential to plant growth. It is absorbed by plants from the soluble compounds in the earth or in fertilizers.

EXPERIMENT 214 - Obtaining potash from wood ashes
Potash was formerly obtained by leeching out the soluble material in wood ashes with water.

Put 4 spoonfuls of wood ashes in a glass half full of water and stir well for several minutes. Now allow this mixture to stand for a few minutes and then filter off a little of the liquid into a test tube. Test this liquid by adding 2 or 3 drops of phenolphthalein solution.  Notice that the solution turns red. Potassium carbonate is found in wood ashes and is removed in this way. By evaporating the liquid down to dryness we could obtain the solid compound.

ALKALINE EARTH METALS, CALCIUM, STRONTIUM, BARIUM

The term "alkaline earth" was originally applied to the oxides of these metals because they resemble both the alkalis and the earths, the latter term being applied to oxides of aluminum and iron.

These metals do not occur free in nature, but largely as carbonates and sulphates.  They are light and active, resembling each other closely in physical and chemical properties. They react with the oxygen in the air and decompose water, liberating hydrogen, similar to the alkali metals.

Calcium carbonate is found in nature in large quantities as limestone or marble.  Also gypsum (calcium sulphate) and phosphate rock (calcium phosphate) occur extensively.
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Lime or calcium oxide is prepared from limestone by heating in large furnaces or kilns.  It is used in making calcium hydroxide and slaked lime.

EXPERIMENT 215 - Burning limestone to quick lime
Obtain a few pieces of limestone, marble or oyster shells and break them up into a powder.

Place some of this powder - 2 teaspoonfuls - on a small tin can lid and heat over a hot gas flame.  Heat so that the limestone becomes white hot and after twenty minutes' heating allow to cool. The compound remaining is quick lime or calcium oxide.  Limestone or calcium carbonate, upon heating, decomposes into calcium oxide and carbon dioxide gas.

EXPERIMENT 216 - Slaked lime or calcium hydroxide
To a test tube add 1/2 inch of powdered lime and 5 or 6 drops of water. Notice that the lime puffs up after a few minutes and appears to be perfectly dry. This forms what is known as slaked lime and is really calcium hydroxide.

Now fill the test tube 1/3 full of water and shake the contents of the tube. Filter off the liquid and test it with red litmus paper. This liquid is a solution of calcium hydroxide.  It is a weak base and is used in medicine as lime water.

Mortar, which is used in stone foundations for buildings, is made by mixing together water, sand and slaked lime. On exposure to the air mortar sets or becomes hard. This is because  carbon dioxide in the air reacts with the slaked lime to form an insoluble calcium carbonate or limestone.

EXPERIMENT 217 - Making mortar
Take three measures of calcium oxide and mix this together thoroughly with three measures of sand. Then add a few drops of water to make a paste.

Spread this paste on a board and allow it to stand for several days. Notice that it soon becomes hard and sets.

Plaster of Paris is made from gypsum or calcium sulphate by heating until all the water is driven off.

EXPERIMENT 218 - To make Plaster of Paris
Take a spoonful of calcium sulphate and heat over the alcohol or gas flame for ten minutes to a high temperature. Allow to cool and then empty the contents of the spoon on a sheet of paper. This is plaster of Paris.

EXPERIMENT 219 - Making a cast with plaster of Paris
Break up the plaster of Paris which you made in experiment 218 into a fine powder and mix a little of this with water to the consistency of a paste. Place a coin slightly greased with oil on a paper. Spread some of this paste on the coin. Press the paste out on the coin to displace any air bubbles and leave the plaster undisturbed until hard.  Then remove it and you will notice a perfect imprint of the face of the coin on the plaster.

It is important to call attention to the application of magnesium chloride and magnesium sulphate in the production of plaster cement used for stucco construction work.  When magnesium oxide is mixed with strong aqueous solutions of these salts, interreactions occur with the formation of oxychlorides and oxysulphates, respectively that have the property of setting like cement. These cements form the basis of stuccos, flooring, synthetic wood, and sound absorbing materials. This material has found a very extensive use for the construction of office buildings and public buildings.
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Calcium sulphide when it contains traces of sulphides of some of the other metals has the property of absorbing light from a luminous body and then giving up light in the dark. It is prepared by heating calcium sulphate with carbon.

EXPERIMENT 220 - Calcium sulphide light
Expose a piece of calcium sulphide paper to a gas or electric light for several minutes.  Now take the paper into a dark room and notice that it is luminous and gives off light.

Certain metals or their compounds impart a characteristic color to a flame. While the alkaline earths resemble each other in chemical properties, they differ in the colors they give to a flame. Calcium compounds give a red flame, strontium gives carmine and barium gives a green flame.

The alkali metals and their compounds also give characteristic colors in a flame.  Sodium gives a yellow flame and potassium a purple flame. Copper compounds give a green flame.

EXPERIMENT 221 - Flame test for metals
Clean the steel wire and make a loop in the cleaned wire. Heat the loop in a flame until there is no color given to the flame by the wire.

Dip the clean wire into some powdered calcium chloride and then heat in the tip of the flame. Notice the red flame of calcium.

EXPERIMENT 222 - Red fire
Mix together thoroughly in a pan one measure of strontium nitrate, two measures of potassium nitrate, one measure of sulphur and two measures of powdered charcoal. Make into a small pile and keeping the face at a safe distance light the pile with a match. Notice that the mass takes fire readily and burns with a red light, due to the strontium. The sulphur and charcoal act as combustible materials, while the potassium nitrate furnishes oxygen for the reaction.

EXPERIMENT 223 - How to make green fire
Zinc, when in the form of a powder, burns with a green flame.

Repeat experiment 222, using two measures of powdered zinc, two measures of potassium nitrate, two measures of powdered charcoal and one measure of sulphur.  Notice that this mixture when ignited will burn with a green flame. These mixtures can be ignited to good advantage by the use of a fuse. The fuse is prepared by soaking a piece of ordinary string in a strong solution of potassium nitrate and allowing the string to dry.

EXPERIMENT 224 - How to make yellow fire
Sodium when burned produces a yellow flame.

Repeat experiment 223, using one measure of dry sodium chloride, two measures of potassium nitrate, one measure of sulphur and two measures of powdered charcoal.  Ignite the mixture and notice that it burns with a yellow flame.

EXPERIMENT 225 - Preparing a safe explosive
Chemicals needed: iodine crystals and ammonia. Apparatus you will need: test tube and filter paper.

Crush several of the iodine crystals and place them in a clean test tube.  Pour in about one teaspoonful of ammonia and let this stand for half an hour.  Then filter it.  Do not let filtrate spill on the table.  Dry the filter paper in dry open air. As soon as it is dry just a scratch on the filter paper will explode the crystals.
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