Scientific Culture, and Other Essays Part 10

Now, the rational system of teaching chemistry is first to present to the scholar's mind the phenomena of Nature with which the science deals.

Lead him to observe these phenomena for himself; then show him how the conclusions which together const.i.tute that system of knowledge we call chemistry have been deduced from these fundamental facts. My plan is to develop this system in the lecture-room in as much detail as the time allotted will permit; to ill.u.s.trate all the points by experiment, and in addition to explain more in detail carefully selected fundamental experiments, which the student subsequently repeats in the laboratory himself. Thus I make the lecture-room instruction and the laboratory demonstration go hand in hand as complementary parts of a single course of teaching.

I begin by directing the student to observe for himself the properties of bodies by which substances are distinguished. I place in his hands a bit of roll-brimstone. He first notices the color, the hardness, the brittleness, and the electrical excitability of this material. He next determines its density, its melting-point, its point of ignition, and, if practicable, its boiling-point. Then he treats the brimstone with various solvents, and finds that, while insoluble in water or alcohol, it dissolves readily in sulphide of carbon. Afterward he evaporates the solution thus made, and obtains definite crystals, whose forms he studies, and compares with the forms of the crystals of the same material which he also makes by fusion. Lastly, he observes the remarkable change which follows when fused brimstone is heated above its melting-point, and also the peculiar plastic condition which the material a.s.sumes when the thickened ma.s.s is poured into water. He will thus be led to see that the same material may a.s.sume different states, and gain a clear conception of the substance we call sulphur. After this I give the student pieces of two metals which externally resemble each other, like lead and tin, in order that, after making another series of observations and experiments, he may come to understand on what comparatively slight differences of properties the distinction between substances is frequently based. A comparison is next made of the properties of two closely-allied liquids, like methylic and ethylic alcohol; and by this time the student attains sufficient skill in experimenting to make a comparison between two aeriform substances, like oxygen gas and carbonic dioxide.

After more or less of such preliminary work, we are prepared to take up the subject-matter of chemistry. In the broad fields of Nature what portion does this science cover? Natural phenomena may obviously be divided into two great cla.s.ses: First, those changes which do not involve a transformation of substance; and, secondly, those changes whose very essence consists in the change of one or more substances into other substances having distinctive properties. The science of physics deals with the phenomena of the first cla.s.s; the science of chemistry with those of the last. Any phenomenon of Nature which involves a change of substance is a chemical change, and in every chemical change one or more substances, called the factors, are converted into another substance or into other substances called the products. The first point to be made in teaching chemistry is, that a student should realize this statement, and a number of experiments should be shown in the lecture-room and repeated in the laboratory ill.u.s.trating what is meant by a chemical change.

Here, of course, arises a difficulty in finding examples which shall be at once simple and conclusive, for in almost all natural phenomena there is a certain indefiniteness which obscures the simple process. The familiar phenomena of combustion are most striking examples of this fact, and men were not able to penetrate the mist which obscured them until within a hundred years. To find chemical processes whose whole course is obvious to an unpracticed observer, we are obliged to resort to unfamiliar phenomena.

A very simple example of a chemical process is a mixture of sulphur and zinc in atomic proportions, which, when lighted with a match, is rapidly converted into white sulphide of zinc, with appearance of flame. Another example, a mixture of sulphur and fine iron-filings, which, when moistened with a little water, rapidly changes into a black sulphide of iron. Then some copper-filings, which, when heated on a saucer in the open air, slowly change into black oxide of copper. Then a bit of phosphorus, burned in dry air under a gla.s.s bell, yielding a white oxide. Next, some zinc, dissolved in diluted sulphuric acid, yielding hydrogen gas and sulphate of zinc. Then, a solution of chloride of barium added to a solution of sulphate of soda, giving a precipitate of sulphate of baryta, and leaving in solution common salt, which can be recovered by evaporating the filtrate.

In all these examples the student should be made to see and handle all the factors and all the products of each process, and the experiments should be selected so that he may become familiar with the different conditions under which substances appear, and with various kinds of chemical processes. He should also be made clearly to distinguish between the essential features of the process and the different accessories, which may be more or less accidental--such, for example, as the water used in determining the combination of iron and sulphur, or the flame which accompanies combustion.

After a clear conception has been gained of a chemical process, with its definite factors and definite products, we are prepared for the next important step. Every chemical process obeys three fundamental laws:

The Law of Conservation of Ma.s.s.

The Law of Definite Proportions.

The Law of Definite Volumes.

According to the first law, the sum of the weights of the products of a chemical process is always equal to the sum of the weights of the factors. This law must now be ill.u.s.trated by experiments, and approximate quant.i.tative determinations should be introduced thus early into the course of study. All that is required for this purpose is a common pair of scales, capable of weighing two or three hundred grammes, and turning with a decigramme. We use in our laboratory some platform-scales, made by the Fairbanks Company, which are inexpensive, and serve a very useful purpose.

A very satisfactory ill.u.s.tration of the law of conservation of ma.s.s can be obtained by inserting in a gla.s.s flask a mixture of copper-filings and sulphur in atomic proportions. The gla.s.s flask is first balanced in the scale-pan; then removed and gently heated until the ignition which spreads through the ma.s.s shows that chemical combination has taken place. The flask is lastly allowed to cool, and on reweighing is found not to have altered in weight.

For a second experiment, a bit of phosphorus may, with the aid of some simple contrivance, be burned inside a tightly-corked gla.s.s flask, of sufficient volume to afford the requisite supply of oxygen. Of course, on reweighing the flask, after the chemical change has taken place, and the bottom of the flask covered with the white oxide formed, there will be no change of weight, and this experiment may be made to enforce the truth that, in this example of combustion at least, the chemical process is attended with no loss of material. Open now the flask, and air will rush in to supply the partial vacuum, proving that in the process of combustion a portion of the material of the air has united to form the white product.

Make now a third experiment as an application of the general principle which has been ill.u.s.trated by the previous experiments. Burn some finely divided iron (iron reduced by hydrogen) on a scale-pan, and show that the process is attended by an increase of weight. What does this mean?

Why, that some material has united with the iron to form the new product. Whence has this material come? Obviously from the air, for it could come from nowhere else. And thus, besides ill.u.s.trating the first of the above laws, this experiment may be made to furnish an instructive lesson in regard to the relations of the oxygen of the atmosphere to chemical processes.

The second law declares that in every chemical process the weights of the several factors and products bear each to the others a definite proportion. This law must next be made familiar by experimental ill.u.s.trations. A weighed amount of oxide of silver is placed in a gla.s.s tube connected with a pneumatic trough. The tube is gently heated until the oxide is decomposed and the oxygen gas collected in a gla.s.s bottle of sufficient size. The metallic silver remaining in the tube is now reweighed, and the volume of the oxygen gas in the bottle measured, and from the volume of the gas its weight is deduced. The measurement is easily made by simply marking with a gummed label the level at which the water stands in the bottle. If, now, the bottle is removed from the pneumatic trough and the weight of water found which fills the bottle to the same height, the weight of the water in grammes will give the volume of the gas in cubic centimetres, and, knowing the weight of a cubic centimetre of oxygen, we easily calculate the weight of this gas resulting from the chemical process. We have now the weights of the oxide of silver, the silver, and the oxygen, the one factor and the two products of the chemical process, and, by comparing the results of different students making the same experiment, the constancy of the proportion will be made evident to the cla.s.s.

For a second ill.u.s.tration of the same law, the solution of zinc in dilute sulphuric acid, yielding sulphate of zinc and hydrogen gas, may be selected, and the weight of the hydrogen, estimated as in the previous example, shown to sustain a definite relation to the weight of the zinc dissolved.

Again, silver may be dissolved in nitric acid, and the weight of the nitrate of silver obtained shown to sustain a definite relation to the weight of the metal.

Or, still further, as an experiment of a wholly different cla.s.s, a known weight of chloride of barium may be dissolved in water, and, after precipitation with sulphuric acid, the baric sulphate collected by filtration and weighed, when the definite relation between the weight of the precipitate and the weight of the chloride of barium will appear.

For a last experiment let the student neutralize a weighed amount of dilute hydrochloric acid with aqua ammonia, noting approximately the amount of ammonia required. Let him now evaporate the solution on a water-bath, and weigh the resulting saline product; taking next the same quant.i.ty of hydrochloric acid as before, and, having added twice the previous quant.i.ty of ammonia, let him obtain and weigh the resulting salammoniac as before. A third time let him begin with half the quant.i.ty of hydrochloric acid, and, adding as much ammonia as in the first case, again repeat the process. It is obvious what the result of these experiments must be; but without telling the student what he is to expect, it will be a good exercise to ask him to draw his own inferences from the results. Of course, he must previously have so far been made acquainted with the properties of hydrochloric acid and ammonia as to know that the excess of either would escape when the saline solution is evaporated over a water-bath. But with this limited knowledge he will be able to deduce the law of definite proportions from the experimental results thus simply obtained.

The third of the fundamental laws of chemistry stated above (generally known as the law of Gay-Lussac) declares that, when two or more of the factors or products of a chemical process are aeriform, the volumes of these gaseous substances bear to each other a very simple ratio. Here, again, numerous experiments may be contrived to ill.u.s.trate the law.

Water, when decomposed by electricity, yields hydrogen and oxygen gases whose volumes bear to each other the ratio of two to one. When hydrochloric-acid gas is decomposed by sodium amalgam, the volume of the original gas bears to that of the residual hydrogen the ratio also of two to one. When ammonia is decomposed by chlorine, the volume of the resulting nitrogen gas is one third of that of the chlorine gas employed.

Having ill.u.s.trated these three general laws, attention should be directed to the fact that the nature of a chemical process and the laws which it obeys are results of observation and involve no theory whatsoever. On these facts the science of chemistry is built. The modern system of chemistry, however, a.s.sumes what is known as the molecular theory, and by means of this theory attempts to explain all these facts and show their mutual relations. Here the distinction between fact and theory must be insisted upon, and also the value of theory for cla.s.sifying facts and directing observation.

A molecule is now defined, and, if the student has not studied physics sufficiently to become acquainted with the outlines of the kinetic theory of gases, this theory must be developed sufficiently to give the student a knowledge of the three great laws of Mariotte, of Charles, and of Avogadro. He must be made to understand how molecules are defined by the physicist, and how their relative weights may be inferred by a comparison of vapor densities. He should then be made to compare the relative molecular weights, deduced by physical means, with the definite proportions he has observed in chemical processes. He will thus himself be led to the conclusion that these definite proportions are the proportions of the molecular weights, and that the constancy of the law arises from the fact that in every chemical process the action takes place between molecules, and that the products of the process are new molecules, preserving always, of course, their definite relative weights. The student will thus be brought to the chemical conception of the molecule as the smallest ma.s.s of any substance in which the qualities inhere, and he will come to regard a chemical process as always taking place between molecules.

Thus far nothing has been said about the composition of matter. A chemical process has been defined simply as certain factors yielding certain products, but nothing has been determined about the relations of these several substances except in so far as they are defined by the three laws ill.u.s.trated above. But now it must be shown that a study of different chemical processes compels us to conclude that in some cases two or more substances unite to form a compound, while in other cases a compound is broken up into simpler parts. Thus, when copper-filings are heated in the air, it is evident that the material of the copper has united with that portion of the air we call oxygen to form the black product we call oxide of copper; and again, when oxide of silver is heated, it is evident that the resulting silver and oxygen gas were formerly portions of the material of the oxide. So, when water is decomposed by electricity, the conditions of the experiment show that the resulting oxygen and hydrogen gases must have come from the material of the water, and could have come from nothing else.

Experiments should now be multiplied until the student has a perfectly clear idea of the nature of the evidence on which our knowledge of the composition of bodies depends. The decomposition of chlorate of potash by heat, yielding chloride of pota.s.sium and oxygen gas; the decomposition of nitrate of ammonium by heat, yielding nitrous oxide and water; the decomposition of this resulting nitrous oxide, when the gas is pa.s.sed over heated metallic copper; and, lastly, the decomposition already referred to, of water by electricity--are all striking experiments by which the evidence of chemical composition may be enforced.

The distinction between elementary and compound substances having been clearly defined by the course of reasoning already given in outline, the next aim should be to lead the student to comprehend how substances are a.n.a.lyzed and their composition expressed in percents. The reduction of oxide of copper by hydrogen gives readily the data for determining the composition of water, which is thus shown to contain in one hundred parts 1111 per cent of hydrogen and 8889 per cent of oxygen.

Another substance whose a.n.a.lysis can be very readily made by the student is carbonate of magnesia. By igniting pure carbonate of magnesia in a crucible (not of course the "magnesia alba" of the shops), the proportions of carbonic acid and magnesia can be readily determined.

Then, by burning magnesium ribbon, and weighing the product, the student easily finds the relative weight of magnesium and oxygen in the oxide.

And, lastly, the proportion of carbon and oxygen in carbonic dioxide is easily deduced from the burning of a weighed amount of carbon. Here the result may be expressed either in percents of oxide or magnesium and carbonic dioxide, or else in percents of the elementary substances, carbon, magnesium, and oxygen.

After making a few a.n.a.lyses like these, the student will be prepared to comprehend the actual position of the science. All known substances have been a.n.a.lyzed, and the results tabulated, so that it is unnecessary to repeat the work except in special cases.

The teacher is now prepared to take a very important step in the development of the subject. If the molecule is simply a small particle of a substance in which the qualities of the substance inhere, then it follows, of course, that the composition of the molecule is the same as the composition of the substance. The percentage results of the a.n.a.lysis of water, or of carbonate of magnesia, indicate the composition of a molecule of water or a molecule of carbonate of magnesia. Thus, 1111 per cent of every molecule of water consists of hydrogen, while 8889 per cent consists of oxygen. Hence it follows that, in a chemical process, the molecules must be divided, and these elementary parts of molecules which a.n.a.lysis reveals are the atoms of chemistry. Moreover, as we know the weights of molecules, both by physical and chemical means, chemical a.n.a.lysis now gives us the weights of the atoms. We have no time to dwell on the details of this reasoning, but the general course to be followed will be evident, and it must be enforced by numerous examples.

a.s.suming that the student fully comprehends the distinction between molecules and atoms--that is, between the physically smallest particles and the chemically smallest particles--he is prepared to master the symbolical nomenclature of chemistry, with a very few words of explanation. The initial letters of the Latin names are selected to represent the atoms of the seventy known elementary substances, and these letters stand for the definite atomic weights which are tabulated in all chemical text-books. The symbols of the atoms are simply grouped together to form the symbols of the molecules of the various substances; the number of atoms of each kind entering into the composition of the molecule being indicated by a subscript numeral.

Lastly, in order to represent chemical processes, the symbols of the molecules of the factors are written on one side and the symbols of the molecules of the products are written on the other side of an equation, the number of molecules of each substance involved being indicated by numerical coefficients.

The atomic symbols, as we have seen, stand for definite weights. In the same way, the molecular symbols stand for definite weights, which are the sums of the weights of the atoms of which each consists, and in every chemical equation the weights of the molecules represented on one side must necessarily equal the weights of the molecules represented on the other. The chemical process consists merely in the breaking up of certain molecules, and the rearrangement of the same const.i.tuent atoms to form new molecules. Again, as the molecular symbols represent definite weights, the equation also indicates that a definite proportion by weight is preserved between the several factors and products of the process represented.

Again, since every molecular symbol represents the same volume when the substance is in an aeriform condition, it follows that the relative gas volumes are proportional to the number of molecules of the aeriform substances involved in the reaction. Thus it is that these chemical equations or reactions are a constant declaration of the three great fundamental laws of chemistry.

In order to enforce the above principles, a great number of examples should now be given which should be so selected as to ill.u.s.trate familiar and important chemical processes, including the all-important phenomena of combustion. In each case, the student, having made the experiment, should write the equation or reaction which represents the process, and should be made to solve a sufficient number of stochio-metrical problems, involving both weights and volumes, to give him a complete mastery of the subject. Such questions as these will test the completeness of his knowledge:

Why is the symbol of water H_{2}O? What information does the symbol CO_{2} give in regard to carbonic-dioxide gas? Write the reaction of hydrochloric acid on sodic carbonate, and state what information the equation gives in regard to the process which it represents.

Of course, such questions may be greatly multiplied, and I cite these three only to call attention to the features of the method of instruction I have been endeavoring to ill.u.s.trate.

But, besides teaching the general principles of chemical science, it is important to give the student a more or less extended knowledge of chemical facts and processes--especially such as play an important part in daily life, or in the arts--and such knowledge can readily be given in this connection. Beyond this I do not deem it desirable to go in an elementary course of instruction. The way, however, is now opened to the most advanced fields of the science. A comparison of symbols and reactions leads at once to the doctrine of quantivalence, and to the results of modern structural chemistry which this doctrine involves.

Among these results there is of course much that is fanciful, but there is also a very large substratum of established truth; and if the student thoroughly comprehends the symbolical language of chemistry, and understands the facts it actually represents, he will be able to realize, so far as is now possible, the truths which underlie the conventional forms.

The study of the structure of molecules naturally leads to the study of their stability, and of the conditions which determine chemical changes, and thus opens the recently explored field of thermo-chemistry. To be able to predict the order and results of possible conditions of a.s.sociation of materials, or of chemical changes under all circ.u.mstances, is now the highest aim of our science, and we have already made very considerable progress toward this end.

But I have detained you too long, and I must refer to the "New Chemistry" for a fuller exposition of this subject. My object has been gained if I have been able to make clear to you that it is possible to present the science of chemistry as a systematic body of truths independent of the ma.s.s of details with which the science is usually enc.u.mbered, and make the study a most valuable means of training the power of inductive reasoning, and thus securing the great end of scientific culture.

XII.

"n.o.bLESSE OBLIGE."

In the former essays of this volume I have earnestly maintained that scientific culture, rightly understood, is a suitable basis for a liberal education; and I have maintained this thesis without in any way attempting to disparage that literary culture hitherto so generally regarded as the only basis on which the liberal arts could be built.

While, however, I have argued that, in the present condition of the world, there is more than one basis of true scholarship, I have fully admitted that for far the larger number of scholars, including all those whose lives are to be occupied with literary pursuits, the old system of education is still the best. Moreover, I have endeavored to point out that scientific culture in no way conflicts with literary culture; that it has a different spirit, a different method, and a different aim; and I have only recommended it as suitable to those who are distinctly preparing themselves for a scientific calling; but I have maintained that for such men scientific studies, rightly followed, may lead to a broad, a n.o.ble, and in the truest sense a liberal education.

I have used the term scientific culture _rightly understood_ in order to mark a distinction; because a great deal that pa.s.ses for scientific scholarship in the world does not imply true scientific culture. In all departments of learning, and not less in scientific than in literary studies, erudition does not necessarily imply a high degree of culture.

We all value the labors of the lexicographer, and the work may be so done as to task the n.o.blest intellectual power; but there is a higher form of literary culture than that which dictionary-making usually implies. So also in science, no amount of book-learning const.i.tutes what we have called scientific culture rightly understood. For example, the ability to pa.s.s an examination on the facts and principles of science is no test whatever of the form of culture we are advocating. Not that we underrate the value of such tests, or of the knowledge they imply; but the ability to master a subject as presented in a text-book, and to state that knowledge in a concise and accurate form, is the normal result of literary, not of scientific culture. The power to do something well is involved in the very idea of culture, and the scholar who can pa.s.s a successful written examination has acquired a power which literary culture chiefly gives, and that this power may be applied to scientific as well as literary subjects is obvious. Here is a most important distinction in connection with our subject. Culture implies the acquisition of some power of the mind in an eminent degree, and such power is constantly a.s.sociated with erudition, simply because it leads to erudition. But when we see erudition without such power, as we often do in every department of scholarship, we perceive at once upon how much lower a level it stands. What very different things are cla.s.sical scholarship and cla.s.sical erudition; and is not the power which the great cla.s.sical scholars possess of interpreting the thoughts of the cla.s.sical authors, and of reproducing their life, the great element of difference between the two?

So scientific culture implies the ability to interpret Nature, to observe her phenomena, and to investigate her laws. The scholar, to whom Nature presents merely an orderly succession of facts and phenomena, knows nothing of true scientific culture. As there is a spirit in the great writers of cla.s.sical antiquity which enn.o.bles the study of the forms in which the thoughts of these authors were expressed, so also is there a spirit in Nature without which facts and phenomena, however well cla.s.sified, create no intellectual elevation. The last century of the world's history has been marked, more than by anything else, by the increase of our knowledge of Nature, and it will be known in history as the age of great discoveries; but valuable as the facts and principles of science certainly are, greatly as they have promoted the well-being of mankind, and important, therefore, as the knowledge of these facts and principles must be to man, yet nevertheless I should never urge the claims of physical science as a basis of liberal education if they could be defended on no other grounds than these. It is here as elsewhere "the spirit which giveth life"; and the power to interpret Nature, and to commune with the intelligence that rules the universe, is the one acquisition which, above all others, gives worth and dignity to the form of culture we have endeavored to advocate in these essays.

Those who regard science simply as utilitarianism, and who value scientific studies solely because they teach men how to build railroads, to explore mines, to extract the useful metals from their ores, or to increase the yield of agriculture, have an even more imperfect conception of what is meant by scientific culture than those to whom science is merely a valuable erudition. It is true that physics and chemistry may be studied as arts rather than as sciences, and we have no desire to underrate the importance of such technical education; but the difference between the two modes of study is as wide as the difference between the artisan and the scholar. In a.s.serting this we do not forget that the occupations of the engineer, the electrician, and the a.n.a.lytical chemist demand a very large amount of knowledge, judgment, and skill, and are rightly regarded as learned professions. But let it not be supposed that skill in such professions is the end or aim of scientific culture; any more than legal skill is the end or aim of literary culture. If literary scholars regard the study of science solely from this point of view, it is no wonder that they think that the tone of scholarship would be lowered if it rested solely on such a utilitarian basis; and, on the other hand, if they could once realize the sublimity of Nature, as Copernicus, Newton, Faraday, and unnumbered others have realized it, this fear that devotion to science must degrade scholarship would disappear.

We are well aware that practical men frequently regard with undisguised contempt the students of theoretical science, and that the greater number of persons seeking a scientific education must look for employment to the practical professions in which this tone too often prevails. But, certainly, a narrow technical spirit prevails quite as often in the professions in which literary scholars chiefly find employment; and the new scientific professions are even more closely dependent on the discussion of theoretical and abstract principles than those which have hitherto been exclusively regarded as liberal. It is an admitted fact, as we have shown in another place, that all the great advances in practical science, all the great inventions, which during the last century have so wonderfully increased the power of man over Nature, may be traced directly to the results of theoretical study. For this reason, if on no higher ground, we have claimed that it is both the interest and the duty of the State to foster and reward scientific investigation. The time is not far distant, if it is not already at hand, when the scientific culture of a people will be one of the chief factors in determining its position among the nations of the world.