Reviewing a physical-science text for grades 8 and 9

Introductory Physical Science
Sixth edition, 1994. 268 pages. ISBN: 1-882057-04-X.
Science Curriculum Inc., 24 Stone Road, Belmont, Massachusetts 02178.

The Authors Are Knowledgeable,
and the Book Is a Delight

Lawrence S. Lerner

Introductory Physical Science is short -- it has only 268 pages, rather than the 600 to 800 pages found in typical physical-science texts -- because the authors are intent on showing students how to do science, not on stuffing their heads with disjointed results. The authors achieve their purpose by guiding the students through the development of a central concept in physical science, which is announced in the book's preface:

The theme of the course is the development of evidence for an atomic model of matter. Rather than broadly surveying the entire field of physical science, we have taken a well-defined path toward this major objective. The method employed . . . is one of experimentation and guided reasoning based on the results of student experiments.

Other themes might have served as well, but the development of the atomic picture of matter works just fine. The student moves through a series of experiments and analyses that amount to an abridged account of the development of chemistry (and of physics, to some extent) from the mid-1700s to the early 1900s. The authors generally ignore the artificial distinctions between chemistry and physics; for example, they never ask the student to waste time by making lists that segregate the "chemical properties" and "physical properties" of matter.

The authors' pedagogical philosophy is set forth in a message to the student, titled "About the Course." Here is an excerpt:

If someone explained that a TV works because invisible gremlins paint the picture on the front of the tube, would you be satisfied? Using the word "gremlin" does not help you understand how a TV works. Nor does the statement "matter is made of atoms" help you much in understanding matter or atoms.

Modern chemistry and physics can give a much more meaningful account of the properties of matter. If this account is to have any meaning for you, we shall have to begin at the beginning. We cannot just throw new words at you. Each step must be filled in with experiments that you will perform. Then all the words and ideas will correspond to something real for you, and you will reach conclusions on your own.

Though the authors do not say that they have arranged their material in a sequence that generally parallels the historical development of chemistry and physics, knowledgeable teachers will recognize this -- especially when they read the first half of the book, which deals with the macroscopic properties of matter. In a series of experiments that use the simplest possible equipment, the student learns to measure the volume and mass of solids, liquids and gases, and he comes to recognize that even these basic quantities must be interpreted carefully. The student starts by measuring the volume of a rectangular solid, then progresses to measuring the volume of a stack of coins, a quantity of water, and an irregular solid. He sees that if the volume of a quantity of sand is measured by two different methods, the measurements give different results; and he is led to understand why this is so, and what it implies about the need for precision in the use of words.

The experiments with gases recreate one of the hard-won triumphs of 18th-century science: the recognition that gases have mass, density and other specific properties. In the crucial experiment, the student puts an Alka-Seltzer tablet into a test tube of water, collects (and measures the volume of) the gas that evolves, and compares the before-and-after weights of the test tube and its contents. The values obtained are not precise, but they suffice to teach two essential points: The density of a gas is typically much lower than the density of a solid or a liquid (by a factor of a thousand or so); and gases must be taken into account during studies of chemical reactions, even though the densities of gases are small.

From this experimental work, the law of conservation of mass emerges naturally. In the other physical-science books that I have seen, it is simply declared as if it were a sacred commandment.

Now the student is guided through laboratory measurements of boiling points, melting points, densities and solubilities, followed by experiments with various separation procedures: solution, filtration, flotation, fractional distillation, fractional crystallization, and paper chromatography. These prepare the student for experiments which involve the synthesis and decomposition of chemical compounds, and which elucidate the law of definite proportions and (later) the law of multiple proportions.

The concept of a chemical element arises from the student's laboratory work, with some help from the book's skillful authors. It is instructive to compare their approach with the one used in a conventional book, Prentice Hall's Chemistry of Matter. The Prentice Hall book just hands down some sacerdotal esoterica from on high:

Atoms are the basic building blocks of all the substances in the universe. . . . [T]here are only 109 different elements. Elements are the simplest type of substance. Elements are made of only one kind of atom. . . . Atoms of elements combine with one another to produce new and different substances called compounds. . . . The combining of atoms of elements to form new substances is called chemical bonding.

In Introductory Physical Science, however, we find real science instead of priestly pronouncements. The student, during his laboratory work, has weighed a sample of sodium chlorate, has heated it and weighed it again, has inspected the substance produced by the heating, and has compared that substance with the starting material. He has carried out a similar process with a sample of powdered copper. He has dissolved copper oxide in water, and he has plated copper onto a strip of zinc. Now, on page 125 of his textbook, he reads:

Heating copper in air is not the only way to produce a reaction with copper. There are many other reactions, and they all have one feature in common: The product of the reaction always has a larger mass than the mass of copper. Neither heating nor electrolysis will change copper into something that has a smaller mass than did the copper with which we started.

Contrast this behavior of copper with that of sodium chlorate . . . . When you heat sodium chlorate, oxygen is given off, and the resulting sodium chloride has a smaller mass than the original quantity of sodium chlorate. We reason, therefore, that sodium chloride is a simpler substance than sodium chlorate.

[Analogous tests show that] sodium and chlorine must be simpler substances than sodium chloride. However, just as with copper, none of the methods that can be used to break up other substances work for either sodium or chlorine. Pure substances that do not break up by heating, electrolysis, reacting with acids, or similar methods are called elements.

The authors emphasize the tentative nature of this definition by telling that Lavoisier, in 1789, classified lime as an element because he could not make it decompose, and he classified chlorine as a compound (for theoretical reasons that later turned out to be erroneous). Those two substances were not reclassified until Humphry Davy, some 30 years later, showed that lime could be broken down and chlorine could not.

Throughout Introductory Physical Science, simple experiments enable the student to arrive at exciting and useful conclusions. After using a droplet of oleic acid to make a monolayer on water, the student (by using just a little arithmetic) estimates the size and mass of an oleic-acid molecule. To compare the level of radon in a basement with the level of radon in a room upstairs, the student uses a vacuum cleaner, some filter paper and an inexpensive Geiger counter. To measure electric charge, he uses a test tube that collects hydrogen from the electrolysis of water. And when this charge-measuring apparatus is used in conjunction with a watch, it becomes an ammeter.

The text pages are peppered with appropriate, thought-provoking problems -- some easy, some moderately hard, a few that are really difficult. A few essay assignments are offered at the ends of chapters, and they differ from all the essay questions that I have seen in other physical-science books. Why? Because they are useful and make sense. Here are a few examples:

A friend wants to use your balance during the summer. Write a complete set of instructions for her so that she will be able to do so successfully on her own without anybody being present to help her. [page 26]

The terms "conserve" and "conservation" have different meanings in science and in everyday life. . . . Write a brief essay explaining the difference . . . . [page 38]

"Seeing is believing" is a common saying. But does "not seeing" imply "not believing"? Neither hydrogen nor oxygen is visible [in an electrolysis experiment performed] in the laboratory. Is there, perhaps, a form of indirect seeing? Express your thoughts on this subject [page 134]

Vacuum tubes were invented early in this century. They played a crucial role in the development of radios and, later, computers. Today they are hardly used anymore, having been replaced by transistors and integrated circuits. Other inventions, such as the steam locomotive and dirigible, have also played an important role in technology only to be replaced by newer inventions. Read about an invention of your choice and write a paper titled "The Rise and Fall of . . . ." [page 248]

The use of fluoride to reduce tooth decay was quite controversial in the past. Today, irradiating fruits and vegetables to reduce spoiling is controversial. Interview your teachers, parents, and friends to assess their feelings on this issue. Try to determine the basis for these feelings. [page 150]

The assignment dealing with irradiation is particularly interesting because many other books have exercises that are similar to that one, except for the final sentence. Those other exercises are useless. Merely assessing "feelings" is, in itself, an empty pastime -- especially if the persons who are surveyed know little or nothing about the subject involved. The assignment in Introductory Physical Science, however, has real merit, because the last sentence points to an important question: Are people's attitudes based on evidence and reason, or on speculation and emotion? This question arises often during debates about public-policy matters involving science.

Introductory Physical Science has a few shortcomings, but they are slight. Some of the photographs of laboratory setups are not clear enough to show important details, and the book's index is too skimpy. It should be more detailed.

As far as accuracy is concerned, Introductory Physical Science is outstanding. While conventional books often have one or two serious errors per page, Introductory Physical Science has only one mistake per ten pages or so, and most of the mistakes are minor. Here are examples drawn from chapters 1 through 6 (the first half of the book):

The "fundamental unit of mass in the metric system" is the kilogram, not the gram (page 15). The hydrometer in figure 3.7(a) has not sunk to the bottom of the container, as the text says; the hydrometer is resting on the bottom because the container is too shallow. The trees shown in figure 4.11 are on Whiteface (not "White Face") Mountain. The text on page 85 includes a non sequitur: "Lead seems to affect young children more than adults. Perhaps this is because lead is not eliminated from the body quickly . . . ." The labels A, B, C and D are missing from figure 5.2. The essay question on page 110 refers to a "sludge test," but the text seems to lack any description of that test. Figure 6.1 shows only one burner, but the introductory text refers to "two burners." On page 114 a question about an electrolysis experiment speaks of the "mass ratio of hydrogen to oxygen," though the student has measured volumes, not masses. In table 6.2, Fluorine is misspelled. And in figure 6.10, the siphon's inlet is lower than its outlet.

The slip-ups that I've noticed in chapters 7 through 12 include some minor mistakes and some items that lack clarity. For example, the caption under figure 7.3 includes an unclear reference to a Geiger counter "held in front." The statement that "Atoms cannot be seen even with strong microscopes" is no longer true (page 154). On page 204, in a passage about hydrogen-production in two electrolysis cells, the authors don't make clear that they are describing the production in each cell (not in the two cells taken together); this leads to ambiguous interpretation of figure 10.9. On pages 231 and 232, the description of the operation of a dry cell is vague (as the Teacher's Guide admits). And the discussion of sacrificial electrodes (on page 234) should be rewritten more clearly.

All in all, however, Introductory Physical Science is a delight, and students who spend a school year with this book will learn a great deal. What is more, they will be very well prepared to take more advanced science courses in high school, because they will have made scientific methodology their own. Still more, the teacher will find pleasure in teaching a course based on this book because the beauty of the subject matter is evident on every page, and the exposition is elegant.

Lawrence S. Lerner is a professor in the Department of Physics and Astronomy at California State University, Long Beach. He served on the panel that wrote the current framework for science education in California's public schools, and he is a director of The Textbook League.

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