Chemistry in the home

Preface

This book is the product of an effort to meet the needs of students who elect chemistry early in their high school course. It aims to train students in scientific thinking and to give them a fund of information concerning the chemistry of everyday things, related to industries and the home.

Much of the theory common to high school chemistries has been omitted, because it has been found to be unnec¬ essary, in fulfilling the purpose of this text. Constant effort has been made to keep the language and style sim¬ ple and to select subject matter suitable for boys and girls in the lower classes of the high school. The book represents the result of many trials and much elimination from an overcrowded field of subject matter.

It would have been impossible to prepare the book without the efficient aid of my colleagues of the Manual Training High School of Brooklyn, New York. I wish especially to thank Dr. Charles D. Larkins, the principal of the school, to whose suggestions the book is primarily due, Mr. Charles Germann, who has read the proof and made numerous suggestions, Dr. William Lamb, Mr. Mattuck, Mr. Holly, and Mr. Foster. Mr. Frank Rexford, of Erasmus Hall High School, Brooklyn, has allowed the use of his food tables for use in the food chapter, and assisted in the preparation of the chapter. Miss J. Jenness, of the Girls High School of Brooklyn, has used the notes in her classes and has made many helpful suggestions.

Contents

E

CHAPTER

I. Physical and Chemical Changes II. Water .

Chapter I Physical And Chemical Changes

Importance of science. Every thinking person realizes that, in order to get the most out of life, it is necessary to understand the laws that govern the world in which we live. The consequences of not understanding, or of disobeying, these natural laws cannot be evaded. The State may make a law ordering us to pay a tax upon bonds which we may own. An unscrupulous person might evade the payment of this tax and thus prevent the carrying out of the law. It is not so with the laws of nature. Nature never employs courts and officers to carry out her decrees. If we violate her laws, the penalty is certain to follow, hence the import¬ ance of understanding and obeying these laws. Moreover, the laws of nature, unlike man-made laws, never change, so that what we learn of them in our study of chemistry, will be of use to us throughout life.

We must not think of physics and chemistry as studies useful only to those who expect to engage in technical pur¬ suits, but as everyday studies that will help us to live more satisfactory lives, because they help us to understand the reasons for the numerous things that we must or must not do if we expect to secure the greatest amount of health and enjoyment from life.

Matter is continually changing. As we consider our everyday life, we see that one of the most striking things about it is, that there is everywhere continual change. Our clothes wear out, iron rusts, trees decay and die, even the rocks that seem so everlasting crumble and change to soil.

Our world, then, is not an unalterable mass, but is in a constant state of change, and what we must do is to learn

to understand and direct these changes, so that they may be for our benefit, and not for our injury. This, man is slowly learning to do.

Until we had learned the cause of decay, we could not know how to prevent it, but now that we understand the rea¬ sons why foods spoil, we can prevent such changes. Scientists are constantly studying these changes which take place, and finding out how to use them to our ad¬ vantage. When we examine these various changes care¬ fully, we find that they are divided into two great classes, physical and- chemical.

Physical changes. When you cut out and make a suit, you have changed the shape of the cloth. You have taken cloth, thread, buttons, and lining. You have changed the relative arrangement of all these materials, but every particle of the cloth, thread, buttons, etc., is still in existence as

PHYSICAL AND CHEMICAL CHANGES cloth, thread, buttons, etc. When the suit is worn, you brush against the furniture, and tiny pieces of the cloth are worn off, but they are essentially the same cloth particles. Such changes as these are called physical changes.

Mixing a batter, boiling water, and the falling of rain are other examples of physical changes; in general the science of physics is the study of such changes. We see ourselves reflected in mirrors, our trolley cars run, we telegraph and telephone, by taking advantage of the laws governing such physical changes. Physical changes are those in which the composition of the small particles of the original substance remains unchanged.

Chemical changes. If we tear up a newspaper, we illus¬ trate a physical change, since every particle of the original paper is still in existence. If, however, we set fire to the paper, a different kind of change takes place. The paper particles disappear, and new substances (a white ash and an invisible gas), having new properties, take their place. Such a change as this is a chemical change, and the study of such chemical changes and the laws which govern them, constitutes the science of chemistry.

Importance of chemical and physical changes. It is difficult to overestimate the importance of the study of these chemical changes. The beautiful colors of silks and ribbons, that so delight the eye, are produced by dyes ex¬ tracted by a chemist from black, vile-smelling coal tar by chemical processes. The rails on which our trolley cars run are possible only because a chemist found how to extract iron cheaply from its ores by chemical changes. The proper selection of foods for the home may be made when we have learned of the chemical changes which each type of food undergoes in digestion, and the body requirements.

Often actions which we wish to study include both physical and chemical changes. In the making of bread, the mixing of the flour and water is a physical change, but the action of the yeast in making the bread light is a chemical change, so that the baked loaf is a result of both physical and chemical changes. Every day, in a hundred different ways we are making use of both physical and chemical changes. Let us at the very beginning try to understand and ap¬ preciate the importance of the study of these physical and chemical changes in their rela¬ tions to our everyday life.

Matter is indestructible. In many of these physical and chemical changes, there seems to be a destruction of matter. When a candle burns, it disappears, and our natural conclusion is that the matter composing it has been de¬ stroyed. It is, howrever, not safe for us to jump at such a conclusion. We know that our impressions are not always to be relied upon. You know how difficult it is to deter¬ mine by your feelings, wrhether a room is at the proper tem¬ perature or not, and how necessary it is to correct your im¬ pression by consulting a thermometer. You know how im¬ possible it is to estimate the size of a room, or to guess a person’s wreight accurately; but wdth a yardstick you can measure the room and w7ith a scales you can find a person’s weight.

You must always try to find a w7ay to test the truth of your impressions, and, in the case of the candle, the test is easy. If you place a candle in a large bottle filled with air, seal the bottle, weigh it, and then set fire to the candle with¬ out opening the bottle (which can be done by the aid of a burn¬ ing glass), you are sure that no matter can either get into or

Fig. 2. — Mat¬ ter is not destroyed in burning.

PHYSICAL AND CHEMICAL CHANGES escape from the bottle (Fig. 2). The candle will burn fpr a time, and then go out. If you allow the bottle to cool, and then weigh it again, you will find that its weight has not changed. That is, the materials making up the candle have formed new combinations with the air, and, these new sub¬ stances, being colorless gases, usually escape our notice. No matter has been destroyed, and no matter has been created, but new substances have been formed, the total weight of which is the same as that of the original candle and air.

Similar experiments verify the fact that the total weight of the new products is always equal to the total weight of the original substances. We can neither create nor destroy matter. All we can do is to change its combinations. This is the Law of the Conservation (or Indestructibility) of Matter : Matter can neither he created nor destroyed.

Matter is anything that occupies space.

A physical change is a change in which no particles of matter dif¬ ferent in composition from the original substance are formed.

A chemical change is one in which the particles of matter in the original substance are so altered that the identity of the indi¬ vidual particles is destroyed.

Law of Conservation of Matter : Matter can neither be created nor destroyed.

1. Name three common chemical changes. Three physical changes.

2. Are the following changes chemical or physical? Rusting of iron. Striking a match. Beating an egg. Making coffee. Sweeping. Digesting food.

3. A ton of coal when burned will produce only about 200 pounds of ash. Is this not a case of the destruction of matter? Explain.

4. Iron rust weighs more than the iron from which it was made. Has not matter been created ? Explain.

Chapter II

Occurrence of water. Water, a tasteless and odorless liquid, is one of the few indispensable substances of the earth. It is found even in places where no visible trace of its presence exists. The paper on which these words are printed contains about 8 %, the solid rocks contain a small amount, and our foods are largely composed of it. The table below shows the amount of water present in some common substances.

Bananas . . . . 75 % Eggs . 74 %

Beef, rib roast . . 44 % Our bodies .... 65 %

Cabbage .... 78 % Potatoes . 78 %

Cheese . 31 % Wheat flour ... 12 %

Properties of water. When we cool water to 32° F.,1 it changes to a transparent solid, colorless in small, and light blue in large, masses. Ordinary ice is not perfectly clear, because the water from which it is made contains air dis¬ solved in it, and, on freezing, this air is distributed through the ice in the form of small bubbles. The freezing point of water is the same as the melting point of ice, namely, 32° F.

1 Our ordinary house thermometers are graduated on what is known as the Fahrenheit scale. Fahrenheit is usually abbreviated to F. The name is given in honor of Dr. Fahrenheit, a German, who devised the scale.

Expansion of water. Most of us are familiar with the fact that solids expand when heated. The next time you cross an iron bridge, see if you can find the expansion joint pro¬ vided to allow for the expansion of the iron. Such expansion joints are used in many places to prevent the straining of the metal that occurs when it is held rigidly and heated. There are many such expansion joints in the steam lines of your school building. Figure 3 shows a section of one of these

Fig. 3. — An expansion joint.

expansion joints used in long pipe lines for steam and hot water. See whether you can find one.

The blacksmith takes advantage of this expansion of iron in putting the tire on a wagon wheel. He makes the tire too small to go on the wheel while cold, but, on heating the tire, it expands sufficiently to allow it to be forced on. When the tire cools again, it shrinks and grips the wheel so tightly that it stays on without bolts or screws to hold it.

Water expands in the same way when heated, but there is an unusual fact about its expansion. If we start with water at 32° F., its freezing point, it contracts on heating, up to the temperature of 39° F., at which point it first begins to expand. At 39° F., then, water has its least volume, and therefore its greatest, or maximum, density.1 That is, a cubic inch of

1 By density we mean the quantity of matter contained in a given volume of a substance. A cubic foot of water weighs 62| pounds. A cubic foot of iron weighs 437| pounds. These numbers express the density of water and iron respectively. Volume for volume, the water at 39° F. weighs more than a cubic inch of water at any other temperature.

As a result, when the surface water cools, it becomes denser and sinks to the bottom. This continues until all the water has reached its temperature of maximum density, 39° F. Then, as the surface water becomes slowly cooler, it becomes less dense, and therefore floats on the surface of the warmer water beneath. The ice forms on the surface and acts as a protective blanket. Because the ice is a poor conductor of heat, the water below freezes very slowly. It is for this

reason that a long cold spell is necessary before we have skating on a pond or lake. The water at the bottom of the ocean has about the temperature of maximum density, 39° F., the year round.

As water freezes, it expands, and it is this expansion that cracks water pipes. You have noticed the forcing up of the

FlGfromYreezPingS1°n caP the bottle in winter, due to

the expansion of the milk in freezing (Fig. 4). This expansion is the reason why ice floats on the water. Can you explain why thick cut glass dishes break, if put into hot water, while thin glass tumblers do not ?

Steam. If we melt ice, and heat the resulting water to . 212° F., and continue the heating, the water boils, that is, changes to an invisible gas called steam.

The mist that is commonly called steam is not steam at all. Notice the spout of the tea-kettle when the water is boiling vigorously. For the space of a half inch from the end of the

iron weighs seven times as much as the water, or a cubic foot of iron contains seven times as much matter as a cubic foot of water. The density of iron, compared to water, is seven.

spout, nothing can be seen ; beyond that point we have the mist formed by the steam cooling and condensing into very tiny drops of water. That is, we have transparent steam issuing from the spout, and beyond this a cloud of condensed steam.

Water boils at 212° F. only when the pressure of the air is normal, that is, when the barometer1 stands at 30 inches. At Denver, the ordinary air pressure is much less than at New York, owing to its elevation above sea level. Water boils in Denver at about 202° F. This makes it necessary to boil foods longer in Denver than in New York, as the tem¬ perature of the boiling water is so much lower there. On the tops of some high mountains, it is almost impossible to hard boil an egg, the tem¬ perature of the boiling water is so low.

Increasing the pressure raises the boiling point.

In a steam boiler, if the pressure is 100 pounds per square inch, the boiling _

. r ig. 5. — A pressure cooker.

point of the water is raised

to 337° F. Advantage is taken of this fact, in boiling meat and vegetables at high altitudes. The food, with water, is pla'ced in a steam-tight vessel, called a pressure cooker

1 A barometer is an instrument that tells what the pressure of the air is. This pressure varies from day to day. When it is sufficient to make the barometer stand at 30 inches, we say that the air pres¬ sure is normal. (See page 97.)

(Fig. 5), and heated. The steam, unable to escape, increases the pressure, this raises the boiling point, and so it is possi¬ ble to cook the food satisfactorily.

Evaporation of water. As found in nature, water usually contains impurities. The purest form is rain water, col¬ lected after the rain has fallen for a time sufficient to wash the dust from the air. If we consider the cycle of water in nature, we shall understand better why our spring and river waters must contain some impurities.

We know that if a pan of water is allowed to stand exposed to the action of the air and the sun, the water disappears. Where has it gone? Since it does not disappear when in a closed vessel, it is inferred that it must have passed into the air. It is not visible, but exists in the form of an invisible vapor. We say that the water has evaporated, and we call the change evaporation.

This same evaporation occurs on a large scale at the surface of the ocean. Sometimes the phrase, “ the sun draws the water/’ is used. This is not exactly true; we should say, “ the water evaporates.” The resulting water vapor mixes with the air. A given quantity of air cannot hold more than a certain amount of water vapor, the exact amount depending upon the temperature. The higher the tempera¬ ture of the air, the more water vapor it can hold.

The air over the ocean absorbs the water vapor which rises from it. The air, laden with water vapor, may be blown inland. When the air cools, it cannot hold as much water and so some of it condenses and forms clouds. Fog and mist are due to the same cause, and are really low clouds. This condensation continues until the drops of water become so large that they fall as rain. Before it can rain, then, it is necessary that the air contain water vapor, and that this air be cooled. This explains why certain regions have more or less rainfall than others.

The water cycle. The rain, in falling through the air, dissolves certain gases from it, and washes out the dust. Notice how dirty the first rain water that falls is, especially in the city. The amount of water that falls each year in the form of rain or snow is very great. It is enough, if it were equally distributed, and fell all at one time, to make a

Fig. 6. — Water table. The ground is saturated with water below the

dotted line.

layer about three feet deep over all the land. This amounts to about 30,000 cubic miles of water.

When the rain strikes the ground, a portion of it sinks in, and slowly passes through the soil, until it meets an impervi¬ ous layer, such as a bed of clay. Here it may accumulate and saturate the soil for some distance above the clay. This reservoir of water contained in the ground is called ground water. It is this ground water that supplies water to wells. The upper surface of the saturated soil is called the water table. This is not necessarily level, but may have a gentle slope. In case this water table rises as high as the surface of the ground, a spring, pond, lake, or stream is formed (Fig. 6).

WEED CHEMISTBY - 2

The height of the water table varies with the amount of rainfall, and hence, during very dry seasons, it may become so low that springs, and even streams, may dry up and cease to run. The spring water flows into a brook, the brook into a river, and the river into the ocean. Thus the water cycle is completed. The water came from, and returns to, the ocean, and this continues over and over again.

How water becomes impure. In passing through the ground, the water dissolves any soluble matter that may be

Fig. 7. — Contamination of well water.

present, and thus becomes somewhat impure. Most of these impurities are harmless, but if the water comes in contact with sewage, it may be so contaminated as to be dangerous to drink (Fig. 7). It can usually be made safe by boiling, and this is a wise precaution to take, in case there is doubt as to the purity of the water.

Distilling water. The commercial purification of water is usually accomplished by distilling it. The water to be purified is placed in a vessel (still), closed at the top, and provided with only one escape pipe. The water is heated to the boil¬ ing point. Most of the impurities, such as salt and calcium sulphate, are not vola¬ tile, and so remain in the still. Many of you have noticed the crust that is formed on the inside of the tea-kettle. This is the result of the evapo¬ ration of the water, leaving the dissolved matters behind. The

. . ... Fig. 8. — Distillation of water.

water m the still

(A, Fig. 8) changes into steam, and this steam passes through the escape pipe, which is surrounded with cool water in the condenser C. Cooling the steam condenses it, and pure water drops from the end of the pipe into D. This distilled water will not be perfectly pure, as it still contains some dis¬ solved gases, but it is so nearly pure, that it is used in the laboratory for chemical work.

This same process, distillation, is used to separate two liquids ’having different boiling points. Alcohol, when it is made, is a very dilute solution of alcohol in water. This mixture is distilled, and as alcohol has a lower boiling point than water, 173° F., it boils first, and on condensing the vapor, alcohol containing only a small percentage of water is obtained. This process, called fractional distillation, is also used to separate crude petroleum, as it is pumped from the earth, into gasoline, naphtha, kerosene, and lubricating oils.

Purifying water. Water as it comes from the ground often contains suspended matter. This is especially true of the waters of the western rivers. This suspended matter may be removed by filtration, or by allowing the water to stand until the suspended matter has settled. The water supply

of cities must sometimes be taken from muddy rivers. It may be cleared by filtering it through large beds of sand. This removes the suspended matter, but does not remove the bacteria, nor the dis¬ solved matter.

Composition of water. Water was long thought to be an element, that is, a substance so simple in its com¬ position that it could not be broken up into other substances. We now know that this is not true, but that water is composed of two gases com¬ bined chemically.

We determine its exact composi¬ tion by means of electrolysis . Pure water will not conduct the electric current, but if a little sulphuric acid is added, it allows the current to pass. This acidulated water is placed in a U-shaped tube, so arranged that an electric current can be sent through the water. The electricity

Fig. 9. — Electrolysis apparatus.

breaks up the water particles, and two gases are set free, one in each arm of the U tube (Fig. 9). There is twice as much of one gas as of the other.

The gas present in the larger volume is named hydrogen, and is noteworthy because it is the lightest gas known, and because it burns with an exceedingly hot flame. The other gas, oxygen, is one of the gases contained in the air, and it is essential to life.

When we pull any substance apart in order to find out its composition, we call the operation analysis. By pass¬ ing the electric current through the water, we analyze it, and find its composition by volume to be two volumes of hydrogen to one volume of oxygen.

Elements. Chemists have analyzed many thousands of different substances to find of what they are composed. The results are somewhat surprising. They show us that all the materials that form our world are made up of only about 83 different kinds of matter, and that by combining these in different proportions, we may make all of the various sub¬ stances that we know. Thus, sugar is found to contain three different kinds of matter, that is, three elements. They are oxygen and hydrogen, the elements that we found in water, and carbon, which is the name chemists give to the black material in coal.

Occasionally a new element is found. Radium is an ex¬ ample of this. It was discovered in 1898 by Madame Curie.

Notice that the definition of element is not a substance that cannot be, but a substance that has not been decomposed into simpler substances. In the past, materials have been thought to be elements, that later have been decomposed. Of the 83 elements known we shall study only a few of the more common ones, as oxygen, hydrogen, chlorine, iron, and sodium.

Compounds and mixtures. When elements combine to form pure, definite substances, we call them compounds. Sugar, salt, and starch are examples. If elements or com¬ pounds are mixed together without any chemical change taking place, we call the result a mixture. Sea sand is a mixture. It contains sand, salt, seaweed, etc., all mixed together, but not chemically combined. Muddy water is another example. The mud is mechanically mixed with the water, and can be separated from it by filtering.

Law of Definite Proportions. One distinction between a compound and a mixture is that the composition of a com¬ pound is always the same, while the composition of a mixture may vary between wide limits. Water has been analyzed thousands of times with the invariable result that its com¬ position is always found to be, hydrogen §, and oxygen J, by volume. Water, then, must be a compound, for we cannot imagine that any accidental mixture of hydrogen and oxygen would always have the same proportions.

Brass is made by melting together zinc and copper. On analyzing different specimens, we find that the percentage of zinc varies from 40% to 75%. Brass, then, must be a mixture and not a compound. These facts give us the Law of Definite Proportions, which may be stated thus : The composition of every pure chemical compound is always the same.

Synthesis of water. We may show the composition of water in still another way. If we mix two volumes of hydro¬ gen with one volume of oxygen, put the mixture in a glass tube, one end of which is closed, set the open end in a dish of mercury, so as to prevent any air from getting in, and then set fire to the mixture, the gases will disappear, and a few drops of water, formed by the combination of the two gases, will appear in the tube (Fig. 10). We can easily set fire to the gases by passing an electric spark between the points of platinum wires which are sealed in the glass tube, so that their ends do not quite touch.

The formation of water in this way is called synthesis.

Chemists can build up in such ways as this a great many substances that na¬ ture makes in plants and animals. Thus we have synthetic indigo, vanilla, cam¬ phor, etc. These are not imitations, but are the real substances, formed by man, instead of by nature, from the materials of which they are composed. Often such synthetic products are cheaper than the natural, and equally good. It is, of course, a fraud when they are sold as natural products, instead of being marked synthetic.

Composition of water by weight. The composition of water by weight can easily be determined. Oxygen weighs, volume for volume, sixteen times as much as hydrogen. Since water is composed of two volumes of hydrogen to one of oxygen, its composition by weight must be two of hydrogen to sixteen of oxygen, or one of hydrogen to eight of oxygen. That is, by weight water is ^ hydrogen and | oxygen.

Fig. 10. — Synthesis of water

Density is the mass per unit volume.

Water boils at 212° F. and freezes at 32°F.

The composition of water by volume is one of oxygen to two of hydrogen ; by weight, eight of oxygen to one of hydrogen.

An element is a substance that has not been decomposed into simpler substances.

A compound is a pure substance composed of elements chemically combined.

A mechanical mixture is a substance composed of two or more in¬ gredients the individual particles of which are not chemically combined, but exist side by side.

Analysis is the pulling apart of a substance to find out of what it is composed.

Synthesis is the formation of a compound from the elements com¬ posing it.

Electrolysis is analysis brought about by electricity.

Law of Definite Proportions : The composition of every pure chemical compound is always the same.

1. Is distilled water free from all impurities? Explain.

2. Is brass an element ? Explain.

3. Name two common elements.

4. Is a lamb chop a compound, an element, or a mixture? Explain.

5. How can you prove that wood is not an element?

6. Does the boiling of water remove the impurities ? If not, why does it make the water fit to drink?

7. How would you distinguish between distilled water and perfectly clear colorless spring water?