The Science Notebook
Gilbert Chemistry - Part 8

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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  In addition, much of the information contained in this book about chemistry and other subjects is outdated and inaccurate.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 141 - 160

GILBERT CHEMISTRY 141

TESTING FOODS

TESTING FOR STARCH

EXPERIMENT 421 - How to make a solution for testing starch
Put one-half measure of tartaric acid and one-half measure of bleaching powder (calcium hypochlorite) in a test tube two-thirds full of water  Shake the contents of the tube until the solids are dissolved. Then add 10 or 12 drops of sodium iodide solution and shake again.  Notice the brown solution which is formed.  This is free iodine in solution and was formed by the action of chlorine gas on the sodium iodide solution.  The chlorine gas was liberated by the action of the tartaric acid on the bleaching powder or calcium hypochlorite.

Save this solution and use it in the following experiments for testing for starch in food and other substances.

EXPERIMENT 422 - Testing for starch in rice
Put three or four grains of rice in a test tube half full of water and boil the water for three or four minutes. Allow the test tube to cool and then add one or two drops of the iodine solution prepared in the preceding experiment. Notice the blue color which is formed.  This is the test for starch.

EXPERIMENT 423 - Testing for starch in potatoes
Boil a small piece of potato about the size of a pea in a test tube half full of water for three or four minutes. Allow the test tube to cool, then add one or two drops of iodine solution.  Notice the formation of a blue color, showing that potatoes contain starch.

EXPERIMENT 424 - Testing for starch in flour
Put one measure of flour in a test tube half full of water and boil the solution for one or two minutes. Allow the solution to cool and then add one or two drops of iodine solution.  Notice the blue color which is formed, showing that flour contains starch.

EXPERIMENT 425 - Testing for starch in corn
Break one or two kernels of corn into small pieces and boil them in a test tube half full of water for three or four minutes. Allow the solution to cool and add one or two drops of iodine solution. Notice the formation of a blue color, showing that corn also contains starch.

EXPERIMENT 426 - Testing for starch in apples
Green fruit contains starch, which is converted into sugar when the fruit becomes ripe.

Satisfy yourself that this is true by boiling a small piece of a green apple and of a ripe apple in separate test tubes half full of water for one or two minutes and adding one or two drops of iodine solution to the cool solutions. Notice that the blue color was formed only in the case of the green apple, showing that starch is present in green fruit.

142  GILBERT CHEMISTRY

THE FOOD CHEMIST - JACK HORNER

"Little Jack Horner, he sat in a corner,
Eating a piece of Mother's Thanksgiving pie,
He stuck in his finger and pulled out a raisin
And applied Gilbert's iron test to satisfy his imagination."

EXPERIMENT 427-Testing a raisin for iron
Select a raisin and wash it with water. Then incinerate the raisin in a porcelain crucible by heating the crucible over your alcohol lamp until the raisin is reduced to an ash. This ash contains only inorganic matter.  Digest the ash in diluted boiling hydrochloric acid solution and filter.  The insoluble residue will be silica.  The iron content of the ash will be dissolved, forming iron chloride.  Apply the characteristic test for iron by adding some of the iron solution to the reagent sodium thiocyanate.  If iron is present red iron thiocyanate will be formed.  Also add some of the iron solution to a mixture of potassium ferro- and potassium ferricyanide solutions.  A blue color will be formed if iron is present.

EXPERIMENT 428 - Testing raisin seeds
Take a clean raisin and remove all of the seeds from the pulp. Then incinerate the washed seeds, and the pulp separately in porcelain crucibles. Test the ash in each crucible for iron. Which contains the most iron, the seeds or the pulp?

EXPERIMENT 429 - Apple seeds
Apply the iron test to the ash of apple seeds.

EXPERIMENT 430 - Quince seeds
Apply the iron test to the ash of quince seeds.

EXPERIMENT 431 - Turnip seeds
Apply the iron test to the ash of turnip seeds.

EXPERIMENT 432 - Cabbage seeds
Apply the iron test to the ash of cabbage seeds.

EXPERIMENT 433 - Beans
Incinerate a bean after grinding to a powder and test the ash for iron.

EXPERIMENT 434 - Sunflower seeds
Apply the iron test to the ash of sunflower seeds.

EXPERIMENT 435 - Lettuce seeds
Apply the iron test to the ash of lettuce seeds.

EXPERIMENT 436 - Wheat kernel
Apply the iron test to the ash of kernels of wheat.

EXPERIMENT 487 - "Tums for your Tummy"
Procure in the drug store a small package of "Tums."  Incinerate one of the "tums" and test the ash for iron.  Dissolve some of the ash from "tums" in water and determine whether the water solution is alkaline or acid by testing with indicators.  Test a "tum" for the presence of sugar.

EXPERIMENT 438 - Popcorn
Apply an iron test to the ash of incinerated popcorn.

GILBERT CHEMISTRY 143

EXPERIMENT 439 - Popcorn balls
Pop some dry popcorn in a corn popper.  Then separate some of the white fluffy material and incinerate. Test the resulting ash for iron.

EXPERIMENT  440 - Grape seeds
Apply an iron test to the ash of some grape seeds.

STARCH AND SUGAR INDUSTRY

before we say anything about this industry, we will discuss briefly how starch and sugar are being made every day by nature in plant life and the changes these substances undergo in animal life.

The carbon dioxide which is always found in the air is made by the heat of the sun to combine with water in the plant tissues to produce a compound formaldehyde.  Formaldehyde in turn undergoes what is known as polymerization in the plant to form sugars.  By polymerization we mean several molecules of the substances combining to form a more complex compound.  The sugar is changed to starch by plant ferments or enzymes.  In the process of converting carbon dioxide and water by the plants into sugar and starch, oxygen is liberated and given off into the air. This process may be expressed very clearly as follows:

1.     CO2                +        H2O                           Sunlight    -->        CH2O                  +               O2
    carbon dioxide         Water in presence                                   Formaldehyde                      Oxygen
                                      of chlorophyll

2.    6CH2O            -->            C6H12O6                        Enzyme  -->                                      C6H10O5
    Formaldehyde                   Dextrose (sugar)                                                                      Starch

Man is  dependent upon plants for starches and sugar. When these foods are taken into the body they are changed back again with the aid of the oxygen which we breathe into the lungs from the air into water and carbon dioxide. The carbon dioxide is constantly being passed out of the body when we breathe the air out of our lungs.

To summarize, then, we can say that carbon dioxide of the air is taken up by plants and oxygen given off.  In animal life oxygen is removed from the air and carbon dioxide given off.  In other words, carbon dioxide sustains plant life but destroys animal life.

Nearly all plant and vegetable matter contains starch - potatoes, corn, wheat and rice containing a large percentage of this substance. Sugar cane and beets on the other hand are the chief sources of sugar and contain large amounts of this substance. 

Starch and sugar come under the class of compounds known as carbohydrates.  That is, they are compounds of carbon with hydrogen and oxygen.  In the United States starch is obtained chiefly from corn, while in Europe potatoes are the chief source.  Starch consists of minute granules.  These granules are composed of a substance known as granulose, which is surrounded by a membrane composed principally of cellulose.  Starch does not dissolve in cold water because the granulose which is soluble in water is protected from the action of water by insoluble cellulose membrane. When heated with water the granules burst and the granulose dissolves, forming the well-known starch paste.

Besides its commercial use in the laundry, starch is manufactured for the purpose of making the commercial products known as glucose, grape sugar, malt glucose, dextrin, British gums and soluble starch. These compounds are all formed from starch

144 GILBERT CHEMISTRY

by hydrolysis with suitable reagents. They are all important compounds and are widely used.  Corn syrup is nothing more than glucose which originally came from starch. 

Cane sugar or ordinary household granulated sugar is obtained from the sugar cane through a process of refining. It is the sweetest of all natural sugars and is called sucrose. It has the formula C12H22O11.  On hydrolysis with acids this sucrose may be broken down into two other sugars, dextrose and levulose, having the same formula C6H12O6, but differing in physical properties.  Levulose is sweeter than dextrose and is the chief component of honey.  Dextrose is found in commercial glucose or corn syrup.  Maltose is the sugar that is formed by the action of enzymes, such as diastase on starch.  It has the same formula as dextrose and levulose and is the sugar from which alcohol and most of the alcoholic liquors are prepared.

EXPERIMENT 441 - How to make potato starch
Peel a fresh potato and after washing it with water cut a piece of it up into very small slices. Place these slices in a mortar, or cup, add a little water, about a test tube full and grind the pieces into a fine pulp by means of a pestle or spoon.  Now add a little more water and after stirring a little with a stirring rod strain the  mixture through a coarse cloth, catching the liquid in a glass.  Fill the glass half full of water, stir a few times and allow the liquid to stand quietly for several minutes. Notice that a white sediment settles out in the bottom of the glass. This sediment is the starch originally contained in the potato. The liquid contains a little of the fibrous material which passed through the cloth on straining.

The principle involved in the manufacture of starch from potatoes in Europe is similar to this, although complicated machinery is used in the manufacture of large quantities and in the purification and separation of starch.

EXPERIMENT 442 - How to make cornstarch
Place about 15 kernels of corn in a mortar, or cup, add a test tube full of water and allow the corn to soften somewhat in the water for several hours. Then grind the kernels up into a pulp by means of a pestle or spoon.

Add a little more water and after stirring a few times, strain the mixture through a coarse cloth into a a glass.  Fill the glass half full of water, stir the mixture a few times and allow the liquid to stand quietly for a few minutes.  Notice the sediment in the bottom of the glass. This is starch originally contained in the corn.

Cornstarch is manufactured extensively in the United States by a method similar to this.

EXPERIMENT 443 - How to make starch from flour
Besides starch, flour contains an organic compound called gluten.  In order to separate the starch from gluten proceed as follows:

Put two tablespoonfuls of flour in a cup and add just enough water to make the flour into a stiff dough.  This can be done by working the moist flour with the fingers until it is kneaded into a round ball the same as your mother does when she prepares bread dough for making bread. Now take this ball of dough and holding it in a glass half full of water work it with the fingers so that all portions of it will come in contact with the water.  Notice that the starch separates from the dough and settles in the water, leaving a very sticky mass of gluten in the fingers.

EXPERIMENT 444 - Changing starch into glucose (sugar)
Put 12 measures of starch and three measures of sodium bisulphate in a test tube half full of water and boil the mixture for 10 or 15 minutes. The starch has now been hydrolyzed by the acid to form glucose.

GILBERT CHEMISTRY 145

In order to tell whether the starch has been completely changed over into glucose pour 4 or 5 drops of the above solution into another test tube, add 2 or 3 drops of sodium iodide solution and 1 measure of bleaching powder.  if the mixture turns blue, there is still some starch present, and it will be necessary to heat the starch and sodium bisulphate solution a little longer, adding a little more sodium bisulphate. If no color is produced when a portion of this solution is tested with sodium iodide and bleaching powder, all the starch is converted over into glucose.

When bleaching powder is added to some of the acid solution containing starch and sodium bisulphate, chlorine gas is liberated which, in turn, reacts with the sodium iodide, liberating iodine. Iodine in the presence of starch gives a blue color.

In order to obtain solid glucose from the above solution of starch and sodium bisulphate, pour the solution into a saucer and allow it to evaporate slowly.  Solid glucose will soon separate out.

EXPERIMENT 445 - Making starch from Bantam sweet corn
Obtain a good ear of Golden Bantam corn. Use a grater to make a pulp and do not use the cobs.  Put an equal amount of water with this pulp.  Put the solution in a fine cotton cloth (a linen cloth will do) and squeeze the juice into another pan.  Allow this to set for 12 hours and pour the water off. A white paste will be left.  Dry this in the sun and you will have a good grade of corn starch.

EXPERIMENT  446 - Manufacture of potato starch
Obtain quite a large potato and by scraping reduce it to pulp.  Mix this pulp with an equal amount of water and then squeeze through a cotton cloth (linen is also good).  Repeat the squeezing operation several times until the pulp is quite free of all water.  The pulp (which we can now call cellulose) remains on the cloth and the starch and water goes through into a container. Allow the solution of water-starch to set for some time and then pour the water off.  The white compound in the bottom of the container is potato starch.  By drying this starch of all water a good quality dry starch will be obtained.

EXPERIMENT  447 - Changing starch into sugar in the body
The starch in foods we eat is converted into sugars in the body during digestion by the action of acids contained in the stomach and in the saliva.

Make a little starch paste by mixing one measure of starch in a test tube with eight or 10 drops of water. Fill the test tube half full of hot water and boil the mixture for several minutes.  Now to the warm starch paste add a test tube one-quarter full of saliva from the mouth.  Shake the contents of the tube and allow the test tube to stand in a warm place, preferably on the back of the stove for a half hour.

Test a few drops of this mixture from time to time in a test tube by adding one measure of tartaric acid and one measure of bleaching powder and two or three drops of sodium iodide solution.  When you fail to get the blue color, the starch is all converted into glucose.

In the United States most of the granulated sugar or sucrose is obtained from the sugar cane which is imported into this country from Cuba. Most of the sugar in Europe, on the other hand, is obtained from the sugar beet.

The process of refining or obtaining sugar from these substances is rather simple.  These substances are first cut up and moistened with water. They are then passed through heavy rollers which squeeze out all the soluble juice. These juices are then filtered to remove any fibrous material, after which they are treated with dry slaked lime which neutralizes the acids contained in the juices and precipitates impurities such as albumens.  The mixture is then filtered and the juice concentrated or evaporated

146 GILBERT CHEMISTRY

in large vacuum evaporators to a heavy syrup. It is then allowed to stand until the sugar crystallizes out.  This is removed and after further purification is ready for the market. The liquid remaining contains much sugar in solution and is usually very dark.  This is sold on the market as molasses. 

EXPERIMENT 448-Sugar as a reducing agent
Put two measures of sodium carbonate and two measures of calcium oxide in a test tube one-third full of water.  Shake thoroughly and warm for a few minutes over a flame.  Now filter off the precipitate of calcium carbonate which is formed in the reaction, catching the sodium hydroxide solution in another test tube.

Now to the test tube containing the sodium hydroxide solution add one-half measure of copper sulphate and shake thoroughly. This gives a green precipitate of copper hydroxide.

To this test tube containing copper hydroxide and sodium hydroxide add eight or 10 drops of corn syrup or honey and heat the solution nearly to boiling.  Notice that the solution turns brown and a red precipitate forms on the bottom of the test tube.  This precipitate is cuprous oxide.

The corn syrup contains a sugar dextrose which reduces the copper hydroxide to cuprous oxide and water. Several of the sugars have this property of reduction and this is due to the aldehyde group (CHO) contained in the sugar molecule.

TESTING FOR PROTEINS

Proteins of which we already have spoken is the class of substances containing nitrogen such as lean meat, the whites or albumen of eggs; the albumen and casein of milk and that part of dry vegetables which is not carbohydrate, oil or mineral matter.  Let us examine a few of these substances for proteins.  When proteins are treated with a base, or alkali, the nitrogen is given off in the form of ammonia.

EXPERIMENT 449 - How to test for proteins in eggs
Put half a spoonful of the white of an egg in a test tube, add 2 measures of calcium oxide and 3 or 4 drops of water.  Warm the test tube over a flame for a few minutes then remove the test tube from the flame and smell at the mouth of the tube. Do you recognize the odor of ammonia? Hold a piece of moistened red litmus paper over the mouth of the tube and notice that it turns blue.

EXPERIMENT 450 - How to test for proteins in milk
Put five or six drops of milk in a test tube, add one measure of calcium oxide and warm the test tube over a flame.  Remove the test tube from the flame and smell at the mouth of the tube.  Notice the odor of ammonia.

EXPERIMENT 451 - How to test for proteins in meat
Put a piece of lean meat about the size of a pea in a test tube, add one measure of calcium oxide and 3 or four drops of water.  Warm the test tube over a flame for a few moments.  Remove the test tube from the flame and smell at the mouth of the tube.  Do you recognize the odor of ammonia?  Potato, although a vegetable, contains a certain amount of protein.

EXPERIMENT 452 - How to test for proteins in beans
Crush two beans in small pieces and place them in a test tube.  Add one measure of calcium oxide and four or five drops of water.  Warm the test tube over a flame for a few moments.  Remove the test tube from the flame and smell at the mouth of the tube.  Do you recognize the odor of ammonia?

GILBERT CHEMISTRY 147

Beans contain about 22 per cent protein material.

EXPERIMENT 453 - Testing for sulphur in proteins
Put a half spoonful of the white of an egg into a test tube and add one measure of copper sulphate and two measures of calcium oxide.  Heat the test tube over a flame and allow the mixture to boil for two or three minutes.  Notice the black precipitate of copper sulphide which is formed, showing that proteins contain sulphur.

BREAD MAKING AND BAKING POWDER

In making bread, baking powder is thoroughly mixed with the dry flour.  Water is then added, the flour is kneaded into a dough and put in a warm place to rise.  Heat nearly always hastens a chemical reaction; that is why dough rises quicker in a warm place than in a cool place.

The moisture plus the tartaric acid act upon the sodium bicarbonate and start the formation of carbon dioxide. Soon the dough begins to rise, due to the gas being liberated.  The powder has been distributed through the mass, so that a million gas bubbles are formed which puff out the dough, making it porous.  During the process of baking, the gas and the remaining constituents of the baking powder are converted into harmless substances.  Most of the carbonates are insoluble compounds and can therefore be precipitated from solutions of their soluble salts by carbon dioxide or a soluble carbonate.  Some of these insoluble carbonates are beautifully colored and make very interesting experiments.

EXPERIMENT 454 - How to make baking powder
Put two measures of sodium bicarbonate and two measures of tartaric acid into a test tube.  Mix thoroughly by closing the mouth of the tube with your thumb and shaking back and forth. Notice that nothing happens. Now add a half test tube full of water and notice the sudden reaction.  These are the two active constituents of baking powder.  The gas liberated is carbon dioxide.

Baking powder is composed of two or sometimes more chemicals which, when dry, are not reactive. When water or moisture is applied the tartaric acid and sodium bicarbonate are put into forms whereby they react readily upon each other, the sodium bicarbonate  giving up its carbon dioxide.  This gas is the same as that formed in the lungs or in soda water.

Baking powders found on the market are of three kinds, named from the kind of acid salt used.  For example, tartrate powders have tartaric acid or acid potassium tartrate (cream of tartar); phosphate powders have an acid phosphate such as lime or potassium; and alum powders have as an acid aluminum sulphate.

The reactions which take place in these different baking powders may be expressed as follows;

1.  Acid potassium tartrate + sodium bicarbonate = carbon dioxide + sodium potassium tartrate (Rochelle Salts).

2.  Acid potassium phosphate + sodium bicarbonate = carbon dioxide + sodium potassium phosphate.

3.  Aluminum sulphate + sodium bicarbonate = carbon dioxide + aluminum hydroxide + sodium sulphate (Glauber°s Salt).

EXPERIMENT 455--How to test for starch in baking powder
Put one measure of baking poweder in a test tube one-half full of water and heat the solution to boiling.  Allow the solution to cool, then add one or two drops of iodine solution.  Notice the formation of a blue color, showing that baking powder contains starch.

148 GILBERT CHEMISTRY

Starch is put into baking powder for the purpose of taking up moisture, thereby preventing the acid salt in the baking powder from reacting with the sodium bicarbonate.

EXPERIMENT 456 - How to test for alum in baking powder
Make a solution of logwood by putting one measure of logwood in a test tube half full of water and heating the solution to boiling.  Allow the liquid to cool, then pour the clear red liquid into another test tube. 

Put three measures of baking powder in a test tube half full of water and add one-half measure of tartaric acid. Notice the violent effervescence due to the liberation of carbon dioxide gas. When the reaction has stopped add two or three drops of the red logwood solution.  If the solution turns reddish-blue, alum is present in the baking powder.  Apply this same test for detection of alum in bread, biscuits, doughnuts and loaf cake.

EXPERIMENT 457 - How to test for copper sulphate in bread
Dissolve one-third measure of tartaric acid and one measure of sodium ferrocyanide in a test tube half full of water. Then put into the test tube three or four pieces of bread to be tested and allow the bread to stand in this solution for one or two hours.  If the solution becomes reddish-brown the bread contains copper sulphate.

Copper sulphate is very seldom used as an adulterant in bread.

TESTING MILK

EXPERlMENT 458 - How to test for coloring matter in milk
Put one measure of sodium bicarbonate in a test tube one third full of milk and, putting the thumb over the mouth of the test tube, shake the contents thoroughly.

Now place a piece of filter paper in this solution and allow the paper to remain in this solution for 10 to 12 hours. At the end of this time remove the paper and examine it.  If it is colored a reddish yellow the milk contains some artificial coloring matter. 

EXPERIMENT 459 - How to test for starch in milk
Heat a half test tube full of milk to boiling and allow the test tube to cool.  Then add one or two drops of iodine solution. lf the milk turns blue, it contains starch.

EXPERIMENT 460 How to test butter
Place a small piece of butter about the size of a pea in your spoon and heat it slowly over a flame.  If the butter foams and froths on boiling the butter is fresh.  On the other hand, if it sputters or pops it is either oleomargarine or renovated butter.

Another test that may be applied to butter to show whether it is adulterated is as follows:

Heat a half test tube of milk until it is very hot.  Then put into the milk a piece of butter about a half inch square to be tested and stir until it is all melted.  Now place the cup in a pan of cold water containing a little ice and stir the milk continually until the milk becomes cold and the butter solidifies.  If the butter is pure or renovated it will solidify into small particles throughout the milk.  If it is oleomargarine it will solidify into one solid cake.

Pure fresh butter contains water and butter fat.  Butter fat consists principally of the fats olein, palmitin and stearin.  The flavor of the butter is due to the presence of a small amount of butyrin, which is an ester of butyric acid and glycerine.

GILBERT CHEMISTRY 149

Oleomargarine is made from the fat of cattle and hogs, together with small amounts of cotton seed oil and milk or butter. The milk or butter is added to furnish enough butyrin to give the butter flavor.

Renovated butter is stale or rancid butter made over by chemical treatment.

EXPERIMENT 461 - How to make casein

Put three measures of sodium bisulphate in a test tube one-third full of water and shake until it dissolves. Now add a few drops at a time with constant shaking some of this solution to a half test tube full of milk.  Notice that suddenly a white curdy precipitate is formed.  This precipitate is casein.  This is the same precipitate that is formed when milk turns sour or curdles. The souring of milk is brought about by the formation of lactic acid due to the fermentation of the milk.

Casein besides being used as a food in cheese has many other important uses today.  It is used in the manufacture of adhesives, paints, in dyeing, in medicine, as electrical insulators and in making plastic masses as in stoneware, toys, etc.  In the manufacture of these things the casein is put through a certain chemical treatment.

SOAP

Most of us are familiar with soap and its cleansing properties but how few of us understand the chemistry of soap making and the part soap plays in cleansing.  Soap was made in early history by treating fat with the lye obtained by extracting wood ashes with water and lime. What really happens when ashes are treated in this way is that potassium carbonate which occurs in wood ashes is dissolved by the water.  This water solution of potassium carbonate then reacts with the lime or calcium oxide to form an insoluble compound of calcium carbonate and a soluble compound of caustic potash, potassium hydroxide or lye as it is commonly called.  Fats or grease, which are compounds of glycerine with fatty acids, are then boiled with the proper proportion of lye.  During the reaction the glycerine of the fat is set free and a compound of the fatty acid with the lye is formed, which is the soap.

If too much alkali is used in making a soap, the soap will contain free alkali which is bad.  If not enough alkali is used the soap will be greasy which is also bad.  It is up to the chemist in a soap factory to determine what the suitable proportions are for every sample of soap to be made.  In making fine soaps, such as Castile soap and the high grade toilet soaps, olive oil is used instead of common fats and in the manufacture of many soaps, perfumes and coloring matters are mixed with the other materials.  Ordinary white soaps are made from cotton seed oil. Cheap laundry soaps are made from impure fats obtained from kitchen grease, bones, etc.  Glycerine soaps are made by melting hard soap and adding an equal amount of glycerine.

The difference between hard and soft soaps is due to the materials contained in them.  Soaps made from caustic potash, or potassium soaps, are soft, while those made from caustic soda or sodium soaps, are hard.

In making hard soap, caustic soda and fat are boiled together and when the contents of the vessel are thoroughly united a strong solution of sodium chloride or common salt is added and the mixture heated again.  The heating is then stopped and the contents allowed to stand for several hours.  During this time the contents of the vessel separate into two portions, the lower one consisting of glycerine, salt and all impurities and the upper one soap.  The glycerine is separated from the water and used in medicine and in the manufacture of high explosives such as nitroglycerine and dynamite. 

Did you ever stop to think what happens when you wash your hands with soap?

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The soap removes grease or oil from your hands by breaking it up into tiny droplets that are washed away by the water. ln other words, when you produce a lather on the hands with soap you emulsify the oil or grease and in this condition it is easily removed.
 
EXPERIMENT 462 - Making soap
Make a solution of caustic soda or lye by putting three measures of sodium carbonate and four measures of calcium oxide into a test tube half full of water and boil for two or three minutes. Allow the tube to cool and when the liquid has settled pour the clear liquid into another test tube.  Now add a piece of lard or butter about the size of a marble and boil the liquid again for a few minutes, being careful that the liquid does not bump out of the test tube. You can prevent this by shaking the tube in the flame while heating.  Notice that the lard or butter dissolves very readily in the hot alkali. Now add three measures of common salt and heat the mixture again for two or three minutes.  Allow the contents of the tube to cool and notice that the soap separates out as the upper layer.  The liquid layer below contains glycerine, salt and impurities.  Try washing your hands with the soap you have made.

EXPERIMENT 463 - Why soap cleanses
Put a little kerosene oil into a test tube one-third full of water and shake the contents of the tube.  Notice that the oil has been broken up into minute droplets.  Allow the tube to stand" and now notice that the oil runs together and rises to the top of the water.

Repeat this experiment, using the white of an egg in place of the water.  Notice that this time the oil is broken up into minute droplets as before, but remains in this condition and does not run together and rise to the top of the water. This forms what is called an emulsion, the oil being emulsified.

Repeat this experiment, using a soap solution in place of the white of an egg and convince yourself that the soap forms a true emulsion with the oil.  It is due to this fact that oil, grease and dirt are easily removed from the hands when washed with soap.

EXPERIMENT 464 - Making liquid soap
Put a piece of toilet soap about the size of a marble in a test tube and add twice the amount of glycerine.  Heat the test tube over a flame until the mixture is all melted together. When this mixture is melted together pour the contents of the test tube into a small bottle and fill the bottle with water. This will give you a liquid soap which can be used on the hands the same as ordinary soap.

EXPERIMENT 465-Chemical films and bubbles
Many times you will have the occasion to use films or bubbles in your laboratory.  You may desire to fill a soap bubble with hydrogen gas. You may wish to use films of soap for defraction experiments.  The common soap bubble will not stand up well, so below we are giving a formula of a soap that will give a good bubble and that will stand up well.

Pure Castile Soap - 1 oz.  (Palm-0il soap is also good)
Distilled Water - 8 oz.
Pure Glycerine - 4 oz.

Cut the soap into thin shavings.  Dissolve in the water.  When the solution is complete as possible, add the glycerine and stir well. On standing, the mixture becomes clear at the bottom. The clear portion is removed and used.

GILBERT CHEMISTRY 151

DETERGENTS


Ordinary soap is a detergent and is made by the action of alkali on fats. During the World War several of the countries of Europe, especially Germany, were cut off from the outside world and as a result, fats became so scarce that they could not be used for making soap This shortage stimulated a search for other kinds of detergent agents.  This led to the discovery of a new type of valuable washing agents. These are designated by the class name “Hymolal Salts," and are alkali salts of sulfated alcohols of high molecular weight. The organic chemist prepares his higher alcohols by application of catalytic hydrogenation to higher fatty acids which are widely distributed in nature.  Lauric acid, for example, which is obtained commercially from cocoanut oil gives, on reduction lauryl alcohol.  Sulfation of this alcohol gives lauryl sulphuric acid, and when this last acid is neutralized with alkali a practical detergent is formed (sodium lauryl sulphate.) These salts are more powerful sudsing agents than the ordinary soaps, they are not affected by hard water, and can be us in both acid and alkaline solutions.  The hymolal salts are manufactured in the form of powders, flakes, bars and liquids. These detergents are being introduced to the trade in this country by Proctor and Gamble Company of Cincinnati, Ohio. The greatest advantage for these detergents over soaps is that they are affected very little by the hardness of water.

SOLVING THE HARD WATER PROBLEM IN THE KITCHEN, LAUNDRY AND BATHROOM

EXPERIMENT 466 - Action of ordinary soap on hard water
Place some very hard water in a basin and try to make a good washing solution by sudsing with some of your mother’s kitchen soap. Note that a large portion of your dissolved soap is used up by the hard water and is turned into insoluble calcium and magnesium soap.  These insoluble metallic soaps are sticky and heavy and settle on clothes, your face and hands, in your hair, and on the surface of your wash bowl and bathtub.  They cannot be removed by rinsing.

EXPERIMENT 467 - Action of ordinary soap on sea water
Secure a bottle of salt water at the sea shore and shake with some ordinary soap.  Note the result.

EXPERIMENT 468 - Soap in acid solutions
Prepare a dilute solution of hydrochloric acid as directed in a previous experiment and treat this acid solution with some ordinary soap. Note the result.

EXPERIMENT 469 - Treating hard water with a hymolal salt
Repeat experiment 468 and treat your hard water with a hymolal salt detergent.

EXPERIMENT 470 - Treating sea water with a hymolal salt
Repeat experiment 468 and treat sea water with a hymolal salt detergent. Note the difference in behavior.

EXPERIMENT 471 - Action of hydrochloric acid solution on soap
Mix a hymolal salt detergent solution with dilute hydrochloric acid solution.  Compare with the results obtained with soap under the same conditions.

152 GILBERT CHEMISTRY

EXPERIMENT 472 - Action of calcium chloride solution on soap
Dissolve some calcium chloride in water and then try to dissolve some common soap in the solution.  Note the formation of an insoluble calcium soap.

EXPERIMENT 473 - Action of calcium chloride on a hymolal salt
Repeat the previous experiment but instead of using soap, stir into the calcium chloride solution a hymolal salt.  Note the difference in behavior.

EXPERIMENT 474 - Action of barium chloride on a hymolal salt
Repeat experiment 473 using barium chloride.

EXPERIMENT 475 - Action of strontium chloride on a hymolal salt
Repeat experiment 473 using strontium chloride.

ALKALINE DETERGENTS AND THEIR BEHAVIOR TOWARDS METALS

Alkaline detergents are used commercially for cleaning metal surfaces.  Chemicals which find wide use for this purpose are sodium hydroxide, sodium carbonate, trisodium phosphate, sodium stearate and sodium metasilicate.  A very interesting and instructive series of experiments can be carried out with these salts as follows: Perform a series of immersion treatment tests with the following metals in sheet form, namely, tin, aluminum, zinc and copper.

IMMERSION TESTS

EXPERIMENTAL PROCEDURE 476 - Immersion test with metal strip
Suspend a small sheet of the metal strip in a one to two per cent solution of the different detergents mentioned above and let the metal remain in contact with the detergent solution for four to five hours at ordinary temperature.  The strip of metal should be weighed before and after immersion.  These experiments will offer an opportunity of using your gravimetric balance and weights.  Note the loss or icrease in weight of each strip.

EXPERIMENT 477 - Tin and sodium hydroxide
Tin and sodium hydroxide

EXPERIMENT 478- Tin and sodium carbonate
Tin and sodium carbonate

EXPERIMENT 479 ~ Tin and trisodium phosphate
Tin and trisodium phosphate

EXPERIMENT 480 - Tin and sodium silicate
Tin and sodium silicate.  Strips of tin may be cut from e clean tomato can.  Strips of metal two inches by one-half inch are large enough for experimental purposes.

EXPERIMENT 48l - Copper sheet
Apply the same series of four experiments using thin copper sheet.

EXPERIMENT 482 - Zine sheet
Apply the same series of four experiments using zinc sheet.

GILBERT CHEMISTRY 153

EXPERIMENT  483 - Sheet aluminum
Apply the same series of four experiments using sheet aluminum. Observe which one of the different metals dissolves in any of the detergent solutions.  Also observe whether gas bubbles are generated.  If gas is generated try to identify it.
 
GUMS, ADHESIVES AND GLUES

Gum arabic, a natural occurring substance, is the essential constituent in the manufacture of gums and adhesive for envelopes and stamps. However, a very good substitute known as dextrin or British gum is now made in large quantities both in this country and in Europe by heating starch and subjecting it to the proper treatment.

Glues are  manufactured by boiling with water properly prepared animal matter, such as skins, bones and fish stock, and drying the solution.

A very good household cement for mending crockery, glass, etc., can be made by using water glass or sodium silicate as the binding agent.
 
EXPERIMENT 484 - How to cement broken glass 
By means of a small camel‘s hair brush, paint the broken surfaces of the glass with water glass.  After the water glass starts to harden, which will require a few minutes, press the two broken surfaces together and allow the glass to remain this way for a day or two.  If on pressing the two surfaces together a little of the water glass squeezes out, rub this off with a damp cloth.  Notice after a day or two that the pieces are held very firmly together.  Glass mended with water glass will not hold together in contact with water, since water glass is soluble in water.

EXPERIMENT 485 - How to mend broken china or porcelain
Make a paste by putting a half spoonful of waterglass and six measures of calcium carbonate in a mortar or cup and mixing with a pestle or spoon.  Now mend the pieces of china or porcelain by painting with a brush the broken surfaces with this paste.  This paste when dry is white and resembles exactly the color of the china or porcelain.

EXPERIMENT 486 - How to mend black crockery
To cement together pieces of black chinaware or porcelain make a paste, using a half spoonful of water glass and six measures of manganese dioxide. Then mend the broken pieces together, using this cement the same way as described in the previous experiment.

EXPERIMENT 487 - How to mend blue chinaware
To mend broken pieces of blue chinaware make a paste, using one-half teaspoonful of water glass, four measures of sodium ferrocyanide and two measures of ferric ammonium sulphate.  Then proceed exactly as before in applying the cement.  The blue color is formed by the action of sodium ferrocyanide on ferric ammonium sulphate.

How could you make a red cement, a brown cement, or a green cement?

EXPERIMENT 488-Another household cement
A very good cement for mending chinaware may be made by making a paste, using a half teaspoonful of the white of a fresh egg and six measures of calcium carbonate.  To mend pieces of broken china with this paste brush some of it on the broken surfaces of the china and quickly press the broken  edges together and allow the mended pieces to stand for a day or two.

154 GILBERT CHEMISTRY

EXPERIMENT 489 - How to make envelope or postage stomp mucilage
Put five measures of sugar, two measures of gum arabic and two measures of starch in a test tube one-half full of water. Shake the contents of the tube and allow the tube to stand for five or six hours. Then heat the contents of the tube to boiling and allow the tube to cool.  With a soft brush paint some of this mucilage on a piece of paper and allow it to dry. Now when moistened with water you will be able to stick the paper to any surface. Postage stamp and envelope mucilage is made similar to this.  In order to keep this mucilage from going bad, a drop or two of some preservative, such as oil of sassafras or wintergreen, must be added.

EXPERIMENT 490 - A common household adhesive paste
Make a starch paste by shaking 12 measures of powdered starch in a test tube one-fourth full of water. Stir a little with a stirring rod if necessary. Now to this paste add half a test tube full of boiling water containing three measures of calcium chloride.  Pour this solution into the test tube containing the starch paste and heat the contents of the test tube to boiling.  Allow the test tube to cool.  This gives a  paste which is very good for ordinary household use, such as pasting on labels.

EXPERIMENT 491 - Another household adhesive paste
Another practical adhesive paste can be made from wheat flour, water and calcium chloride. 

Put eight measures of ordinary wheat flour and two measures of calcium chloride in a test tube one-half full of water. Heat the test tube over a flame and boil the contents of the tube until it becomes thick and pasty.  Then stop heating and allow the test tube to cool. 

In order to keep the pastes prepared in the last two experiments for any length of time one or two drops of a preservative, such as oil of sassafras or wintergreen oil must be added.

EXPERIMENT 492 - Labels for your bottles
Cut small pieces of adhesive tape from the roll and stick on the bottles. Then write the name of the chemicals or the formula on the tape with a pen and ink and varnish the label.  However, you can purchase gummed labels at your local drug store quite cheaply. LABEL ALL POISON BOTTLES WITH POISON!

INK

Most of the common black inks are made from nut galls and ferrous (iron) sulphate.  The nut-galls are rich in tannic acid and this with ferrous sulphate gives a black precipitate. Colloidal or jelly-like substances, such as gum arabic or dextrin are sometimes added, as these substances delay the precipitation, although the very black color is produced at once.  Some preservative is usually added to prevent the ink from moulding.

Today very good black inks are made from derivatives of the organic compound aniline.  Aniline is a compound obtained indirectly from coal tar. 

Much time has been devoted to finding an ink that would be permanent and resist all attempts to remove it from paper. Most inks can be erased from paper without much difficulty.  Printer's ink, however, which is made from lampblack has been found to be the most permanent, as the finely divided carbon which is held firmly within the pores of the paper is insoluble in all liquid solvents so it cannot be removed by washing.  lt is also very difficult to erase it without destroying the paper.

GILBERT CHEMISTRY . 155

Silver nitrate, when in contact with an oxidizable material such as cloth, is reduced in the presence of light to black metallic silver. Because of this fact it is used in the manufacture of indelible inks.

Quite often it is desirous of making several copies from a single document. In order to do this an exact copy of the document is made on heavy paper, using copying ink.  The desired copies are then made by using very thin unsized paper and placing them on the copy prepared with copying ink.  Pressure is then applied to the copies so that the inks penetrate through the duplicates. It is possible by this method to prepare as many as a dozen duplicate copies at one time from the original copy.

EXPERIMENT 493 - How to make black writing ink
Dissolve one measure of tannic acid in a test tube one-third full of water. Then in another test tube one-third full of water dissolve one measure of ferric ammonium sulphate.  Now mix the two solutions and notice the intense dark black color formed by the reaction of the two substances.  The black color and precipitate is due to the formation of iron tannate.  Try writing with this ink, using a clean pen.

If you wish to make up a bottle of black ink to use permanently proceed as follows:  Dissolve four measures of tannic acid in a test tube three~quarters full of water.  Pour this solution into a glass containing six test tubes full of water.  In another test tube three-quarters full of water dissolve four measures of ferric ammonium sulphate and one measure of gum arabic.  Heat the test tube in order to dissolve these substances.  Then pour the contents of this tube into the glass and stir well with a stirring rod.  Add one or two drops of oil of wintergreen to keep the ink from moulding and pour the ink into a bottle.  This will give a black writing ink that can be used from time to time.

EXPERIMENT 494 - How to make blue ink
Prussian blue ink may be made by dissolving two measures of ferric ammonium sulphate in a test tube one-third full of water and adding this solution to a solution of sodium ferrocyanide made by dissolving two measures of sodium ferrocyanide in a in a test tube one-quarter full of water.  The blue precipitate formed in the reaction is a compound of ferro-ferricyanide.  Write with the ink.

EXPERIMENT 495 - How to make purple ink
Put three measures of logwood into a test tube one-third full of water and boil for several minutes until the solution is deeply colored.  Then add 1 measure of aluminum sulphate and heat to boiling again.  Notice the beautiful dark colored purple ink  which is formed.  Write with the ink using a clean pen.  By repeating this experiment and adding one measure of sodium bisulphate in addition to the other compounds, it is possible to make a red ink.  Write with an ink made in this way, using a clean pen.

EXPERIMENT 496 How to make carmine ink
Put two measures of cochineal in a test tube one-third full of water and boil for several minutes until the solution is deeply colored.  Cool the solution, and, using a clean pen, write with it.  Notice that this gives a crimson or purplish-red ink. This color is due to carminic acid occurring in cochineal.

EXPERIMENT 497 - How to make a green ink
Put two measures of nickel ammonium sulphate and one measure of sodium ferrocyanide in a test tube one-third full of water and shake well.  Now add one-half measure of ferric ammonium sulphate and shake well again.  Notice the formation of a deep green color and precipitate.  Write with this solution using a clean pen.

156 GILBERT CHEMISTRY


EXPERIMENT 498 - How to make a commercial blue-black ink
Put one measure of ferric ammonium sulphate and one measure of tannic acid into a test tube one-third full of water and shake well. In another test tube one~quarter full of water add one measure of sodium ferrocyanide and one measure of ferric ammonium sulphate and shake thoroughly.  Mix the two solutions and notice the bluish-black ink produced.  Write with this ink, using a clean pen.  Notice that the writing is blue. After two or three days the writing will turn black.

EXPERIMENT 499-How to make printer's ink
Put a spoonful of water glass (sodium silicate) in a test tube and add two measures of powdered charcoal or better, lampblack.  By means of the stirring rod, stir the mixture until it is quite uniform.  Then fill the test tube one-third full of water and shake thoroughly.

Now add one measure of ferric ammonium sulphate and one measure of tannic acid.  Shake thoroughly for several minutes and notice the heavy dark black liquid produced.  Printer's ink is made similar to this.  Writing done with this ink will last for a long time and is very difficult to remove.  This is because the charcoal or lampblack gets into the pores of the paper where it is held fast.

EXPERIMENT 500 - A commercial ink powder
Mix together on a sheet of paper three measures of tannic acid, six measures of ferric ammonium sulphate, and six measures of sodium ferrocyanide.  Place this mixture in a small dry bottle and whenever you wish to make a good blue-black ink add water to the bottle and shake thoroughly.

EXPERIMENT 501 - A red ink powder
Crush into the form of a powder a little cochineal by grinding it in the mortar and put five or six measures of the powder into a small dry bottle.  Whenever you wish red ink simply add water to the bottle and shake thoroughly for several minutes.

EXPERIMENT 502 - An ink remover
Dissolve one measure of tartaric acid and one measure of calcium hypochlorite (bleaching powder) in a test tube one-third full of water. 

By means of a small camel’s hair brush, paint the ink to be removed with some of the solution just prepared and notice that the ink disappears. The bleaching powder and tartaric acid react to form chlorine gas, which in the presence of water bleaches the ink or makes it colorless. Not all inks can be bleached in this manner.  Prussian blue for example is not affected by this solution.

EXPERIMENT 503 - Ink powder 
Mix together one measure of tannic acid and one measure of ferric ammonium sulphate. Place the powder thus formed in a small bottle, and when you need ink simply add some of this powder to a little water.

EXPERIMENT 504 - Blue ink powder
Blue ink powder may be made by mixing together two measures of sodium ferrocyanide and one measure of ferric ammonium sulphate.  When this powder is mixed with water you have blue ink all ready to write with.

EXPERIMENT 505 - Red ink powder
Put two or three measures of cochineal in your mortar and grind the material up to a fine powder.  When this powder is mixed with water it will make red ink.  Ink powders are sometimes very convenient to use.

GILBERT CHEMISTRY 157

EXPERIMENT 506 - How to make carbon paper
Obtain a cake of Ivory soap and by scraping the soap with a knife, make a pile of fine soap shavings. Put 15 measures of the soap shavings in a glass or cup. In a test tube one-third full of water, put one measure of sodium ferrocyanide and one measure of ferric ammonium sulphate and shake thoroughly until the solids are all dissolved.  Pour this blue solution into the glass or cup with the soap shavings and stir thoroughly for five minutes until the mixture forms a smooth thick paste.

Now using a small brush or piece of absorbent cotton spread this paste smoothly over a piece of paper.  Set the paper away to dry for a day and then use it like you would ordinary carbon paper.

EXPERIMENT 507 - How to make blue typewriter ribbon
Obtain a quantity of soap shavings by scraping a piece of Ivory soap with a knife.  Put 15 measures o these shavings in a glass or cup and add four or five drops of glycerine. 

Now dissolve one measure of ferric ammonium sulphate and one measure of sodium ferrocyanide in a test tube one~half full of water.  Shake this solution well so that the solids will be entirely dissolved and then pour it into the glass or cup containing the soap shavings and glycerine.  Stir this mixture with your stirring rod until it forms a smooth paste.

Now get a piece of cloth or tape about the width and thickness of a typewriter ribbon and apply the paste which you have made evenly to the cloth or tape.  Now hang the tape up to dry for half an hour or so and then roll it up into a roll just like a ribbon. In order to use it on a typewriter you will of course have to roll it on to an empty spool of the same kind used on your typewriter.

EXPERIMENT 508 - A finger print record
Prepare some blue ink as in the experiment "Blue Ink."  Paint the thumb or finger with the blue solution.  Do not get too much solution on the finger, but just cover it thinly.  Now press the finger against a clean sheet of white paper being careful not to smear, and there you have your finger print.  An album can be made by taking the finger prints of all your friends and marking them.  Wash your hands after taking your finger print.

EXPERIMENT 509 - Detecting finger prints
Obtain a smooth piece of white paper, breathe on one of your fingers a few times and press it on the paper.  Prepare a mixture of one measure of sulphur and one measure of powdered charcoal.  Put this mixture on the paper which you have touched with your finger and tap the underneath side of the paper gently so that the powder will be spread over the part of the paper where you have pressed your finger.  Shake the excess powder off the paper and you will find that the finger prints instead of being invisible are now plainly seen.

EXPERIMENT 510 - Blue Ink
Dissolve two measures of sodium ferrocyanide in a test tube one-quarter full of water.  In another test tube dissolve one measure of ferric ammonium sulphate.  Pour the second solution into the first.  Prussian blue will be formed.  Try to write with the ink.  Prussian blue is used in laundry blueing.

EXPERIMENT 511 - Violet ink
Put two measures of logwood in a test tube one-quarter full of water.  Warm to extract color and then add one-half measure of aluminum sulphate to the hot solution.

158 GILBERT CHEMISTRY

EXPERIMENT 512 - Lemon ink
Dip your pen into a container of lemon juice and write as if with regular ink.  Upon heating the paper, your writing will become visible.

EXPERIMENT 513 - Red ink
Put two measures of logwood in a test tube and fill tube one-quarter full of water.  Warm to extract color and add one-half measure of aluminum sulphate and one-half measure of sodium bisulphate.

EXPERIMENT 514 - Safety ink
Put one spoonful of water glass in a mortar or cup and stir in one measure of powdered charcoal.  Stir for some time to properly mix.  Keep bottled up in a tight stoppered bottle if it is desired to keep for any length of time.  Writing done with this ink is very hard to remove.

EXPERIMENT 515 - Copying ink
Place in a test tube one measure of sodium ferrocyanide and one-half measure of ferric ammonium sulphate.  Fill test tube one-quarter full of water and shake to dissolve salts.  Blue ink is formed.

Now add to this 10 drops of glycerine. Shake. Write on paper with this mixture making your letters very large. Lay the copy on a flat surface and spread over it a  piece of soft tissue paper and then a piece of damp blotting paper and over the blotting paper place a board. Press down on the board an then remove the board and blotting paper and see if you have produced a readable copy. The copying ink should have penetrated through the tissue paper so that writing will appear on reverse side.

EXPERIMENT 516 - Making a camphor ball float
Fill a wide mouth bottle with vinegar and drop some camphor balls into the vinegar and sodium bicarbonate. Carbon dioxide will be generated and little bubbles of gas will collect on the camphor balls.  Soon the camphor balls will become "lighter" and will float to the top of the vinegar and sink again.  This process is repeated several times.

EXPERIMENT 517-Formation of lead iodide
In a convenient sized test tube place two spoonfuls of water and add six drops of sodium iodide solution.  In another test tube place about one measure of lead nitrate or lead acetate obtainable at any drug store and dissolve by adding about one test tube of water.  Now pour the lead 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 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 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 518 - Magic transfer solution
This solution transfers pictures to cloth, paper dishes, etc., in their original color.  The solution is made as follows: common castile soap, half bar; turpentine, quarter pint; water, half gallon.  Dissolve the soap in the water and then add the turpentine.  To use, apply with a small brush to any printed page or picture and the lay a clean

GILBERT CHEMISTRY 159

paper or cloth over the picture and rub quite hard with the back of a spoon. To transfer to glass or or to dishes use white varnish and do the same as above.  You can make up a few bottles of this solution and sell some to your friends at school.

EXPERIMENT 519 - 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 of a reddish-brown color.  Add to this an eighth test tube of carbon tetrachloride. The carbon tetrachloride 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 of 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 the water and it is not miscible with water.

FERMENTATION

Fermentation is the decomposition or breaking down of complex organic compounds into simpler substances by certain living organisms called ferments. There are many different kinds of fermentation depending on the different kinds of organisms or ferments.  The most familiar illustration of fermentation is the fermentation of fruits or fruit juices, the decay of vegetable matter or nitrogenous matter, the souring of cider or of milk and that taking place in bread making by action of yeast.  Most organic substances, especially the complex substances, are subject to fermentation changes.  The chemical changes brought about by ferments consist in the breaking down of complex molecules to form simple groups of atoms. In some cases it consists in a rearrangement of the atoms in the molecule to form a compound with different properties.  There are many kinds of living organisms or ferments, each of which produces its special change. Most ferments are microscopic plants of simple structure  which multiply very rapidly when placed in the proper medium or substance.  They are variously known as microbes, germs and bacteria. Yeast which is used so commonly in bread making is a microscopic plant found in the air and about certain fruit trees.  The yeast cakes which you buy in the store are these same living organisms which have been grown in some suitable culture medium as the potato or corn meal.  The above class of ferments are known as organized ferments. The other class of ferments are called chemical or unorganized ferments and are known as enzymes. Examples of these are pepsin, trypsin and diastase.

The action of ferments on organic substances always works best at definite temperatures.  Above these temperatures the ferments or organisms are destroyed or their action  delayed.

EXPERIMENT 520 - Changing sugar into carbon dioxide
Put two spoonfuls of corn syrup or molasses in a tumbler half full of water and stir it up.  Then dissolve one~quarter of a cake of yeast in a small tea cup full of lukewarm water. This is best done by allowing the yeast to stand in the water for about a half hour and then stirring.  Now pour the solution of yeast into the tumbler containing the syrup and set the tumbler aside in a warm place for several hours.  Notice that after some time a reaction is taking place, small bubbles of gas being agiven off.

Hold a lighted match over the surface of the liquid in the tumbler an notice that it goes out, due to the carbon dioxide gas which is given off.  The syrup or molasses contains a large amount of sugar and during the fermentation produced by the yeast this sugar is changed into carbon dioxide gas.

160 GILBERT CHEMISTRY
 
EXPERIMENT 521 - Changing starch into sugar and carbon dioxide 
Put a half teaspoonful of starch in a tea cup and add a spoonful of water. Stir the starch in the water until it is in the form of a paste and then fill the teacup three-quarters full of boiling water and stir for a few moments. Now dissolve one-quarter of a cake of yeast in a teacup One-quarter full of luke warm water and put this solution into teacup containing the starch. Set the teacup away in a warm place and examine it carefully from time to time.  Notice the formation of bubbles of gas, due to the liberation of carbon dioxide gas. It will require several days before the starch will be converted into sugar and carbon dioxide.  
 
This illustrates the way starchy foods are converted in the body into sugars which, in turn, are burned up through the process of assimilation into carbon dioxide and water.
 
EXPERIMENT 522 - The formation of mould
Mould is another form of ferment. You have probably noticed the formation of mould on such substances as sour milk, vinegar and starch which have been exposed to the air for some time. These substances contain the proper food material for certain bacteria in the air.  As a result these bacteria, under proper condition of heat get into these substances and multiply very rapidly, producing the mould.
 
Prepare a starch solution as follows: Put a half spoonful of starch in a tea cup and add one spoonful of water. Stir until the starch forms a paste with the water.  Then fill the cup with boiling water and stir until the starch forms a very gelatinous paste.  It may be necessary to boil this mixture in a tin cup or pan for a few minutes to form a heavy paste.
 
Now set the starch solution aside in a warm place for a few days and notice after some time the formation of mould on the surface of the starch. 
 
EXPERIMENT 523 - Growth of mould
Place one-half teaspoonful of ordinary starch in a small pan and add to this a small amount of water.  Stir to form a perfect paste and then add about one-third of a cup of boiling water.  Set the pan on a stove and continue to boil until a perfect paste is formed.  This paste is now bacteria free.  Finally pour the paste into an ordinary tumbler and set it away in a warm place. It will soon become infected with bacteria from the air.  Examine it from time to time and notice when mould begins to form.  After some mould has formed examine its appearance under a microscope.
 
EXPERIMENT 524 - Composition of mould 
Carefully remove some mould from the surface of the starch mixture and test it for sugar, starch, protein and ammonia.
 
EXPERIMENT 525 - Sugar fermentation
Dissodve one spoonful of ordinary sugar in about one~half cup of water, using an ordinary tumbler for the experiment.  Place in the sugar solution a small piece of yeast, which has first been masticated with water to form a paste and set aside in a warm place to stand.  Notice what happens after a few hours.  Test the gas that is generated.  Will it burn?  Will it dissolve in water, in sodium hydroxide solution?
 
EXPERIMENT 526 - Fermentation of corn syrup
Apply the previous experiment using commercial corn syrup or ordinary molasses.
 
EXPERIMENT 527 - Making vinegar  
Take about one cup of freshly made sweet cider and add to this two or three drops of strong vinegar.  Place the mixture in an ordinary tumbler and set aside, after covering with a plate or piece of cardboard to keep the dust  out.  At the end
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