(10 Feb 1846 - 4 Mar 1927)
UNSOLVED PROBLEMS OF CHEMISTRY.
By IRA REMSEN, LL.D.,
Professor of Chemistry at Johns Hopkins University
from McClure's Magazine (1901)
[p.136] THE first duty of the chemist is to examine every kind of matter accessible to him and to determine whether it is an element or not. If it is not, and this is usually the case as regards the things found in nature, his next duty is to attack the compound in every way that is likely to lead to its decomposition, and when he reaches a substance from which he cannot get simpler ones, he calls this an element. Thus iron, copper, gold, silver, tin, hydrogen, and oxygen are elements. None of these can be decomposed by the means at present at the command of the chemist. They are like the letters of a language in some respect. Words can be decomposed or resolved into letters, but letters are the elements of language. What elements are in the earth, in the air, in water? An immense amount of work has been done that has had for its object the answering of this question. The earth has been ransacked almost from pole to pole. The air from all sorts of localities has been examined. The waters, from ocean, rivers, and springs, have been made to stand and answer the searching questions of the chemist; and animals and plants have been compelled to give up their secrets—or some of them.
What is the result? In brief, it is this: Although we find an infinite number of kinds of matter, all of these can be resolved into a comparatively small number of elements. Indeed, not more than a dozen of these elements enter into the composition of the things that are at all common. But by going into out-of-the-way corners rare things have been found, and from these, in turn, rare elements have been obtained. Altogether, between seventy and eighty elements have been found. Additions are made to the list from time to time; and, occasionally, one of the substances supposed to he an element is [p.137] found to be capable of decomposition, and it therefore becomes necessary to strike it from the list of elements.
Out of these simplest forms of matter everything that we see or feel, or are in any way cognizant of, is made up. But now arises the deep question: What is an element? To this question chemists are not able to give an answer. The relations of the elements to one another form one of the unsolved problems of chemistry. It may be that they are not related at all, but that each one is an independent form of matter. There are, however, indications of family relationships between them that have long been the subject of investigation. The elements fall into groups, the members of which resemble one another very closely in some respects. Thus, for example, phosphorus and arsenic conduct themselves, in general, alike toward other elements. They combine with them to form compounds that are very much alike — so much so that in some cases it is difficult to tell them apart. These elements are said to belong to the same family. The family traits are easily recognized in them. Similar relationships are met with throughout the entire list of elements. This subject has been beautifully worked out by the Russian chemist Mendeléef and the German, Lothar Meyer. The former, indeed, pointed out, thirty years ago, that some of the families are not complete. There were a number of vacant chairs. He was able to predict the discovery of some of these missing members and to describe them in detail. Three of these have since been discovered, and they have been found to answer the description given by Mendeléef before their discovery. Now that the way has been pointed out, it is a comparatively simple thing to predict the discovery of other elements. The vacant chairs are there, but though the elements that are eventually to occupy them are probably hidden away somewhere in the earth, they have thus far eluded the chemist.
As regards the character of the relationships that exist between the elements, it is difficult, or, rather, quite impossible, to speak with confidence. Apparently, the elements are brothers and sisters. We want to find the fathers and mothers. But it appears that they are no longer living. The plain question that we cannot help asking is: Have the elements existed from the beginning of time, or have they been formed from a smaller number of simpler forms of matter? Of course, one can [p.138] speculate on such a subject, but can one speculate profitably? It may as well be acknowledged at once that we know practically nothing in regard to the origin of the elements, or of the cause of the relationships that are so easily recognized.
It has been suggested that the elements are the products of an evolutionary process that has been in progress from the beginning, and that they all owe their existence to a primordial form of matter, simpler than any one of the so-called elements. Some evidence in favor of this view seems to be furnished by the spectroscopic examination of celestial bodies. The nebulae have been shown to contain the smallest number of our chemical elements; the hotter stars are somewhat more complex; in the colored stars and the sun a large number of elements appear; while the planets are the most complex. The complexity seems to depend upon the temperature. The higher the temperature, the smaller the number of kinds of matter present. Now, may it not be that the elements known to us are derived from simpler forms, or from one single simplest form? We can only answer—it may. If this is the true conception of the relations between the elements, then “in the beginning” space must have been filled with an incandescent vapor made up of the simplest form of matter. As this has cooled, it has taken other forms, and some of these are the things we now call elements. But this shows how easy it is to relapse into the ways of our forefathers and let our imaginations run wild.
ELEMENTS OF PLANTS AND ANIMALS
ANOTHER unsolved problem of chemistry is that presented by the fundamental constituents of plants and animals. No one knows better than the chemist that all living things are “fearfully and wonderfully made.” Plants take materials of various kinds from the air and from the earth, and work them up in proper shape for their growth. In turn, animals take parts of some plants or parts of some animals, and work them up so that they become part and parcel of the animal bodies. Life and growth of plant and animal depend upon this power to convert food into other things that can take their proper places in the body. Chemical change is the beginning of life. But what are these things that are formed within the plant and animal? That is a hard question to answer; and, indeed, the answer would be confusing. All that need be said is that among these things are the fats, sugar, starch, cellulose, and a group [p.139] of important compounds called proteids. Besides these, there are innumerable substances found both in plants and animals. Naturally, chemists are interested in these things, and they have given, and are giving, much time to their investigation. It is only through such study that we can hope ever to gain any conception of the changes that are taking place in living things, or of the nature of life in its various forms.
Of the substances mentioned, the fats are relatively the simplest, and they are, accordingly, pretty well understood. It is interesting to note in passing that the first and the most important chemical investigation in fats was carried out at the beginning of this century by the French chemist Chevreul, who died only a few years ago at the age of 103, having kept in harness to the last. Regarding our knowledge of fats, it is safe to say that we know enough about them to be able to see how one could, starting with carbon, hydrogen, and oxygen, which are the only elementary substances found in the fats—how one could make in the laboratory the same fats that occur in living things. No one has ever done this, but it appears highly probable that, with unlimited time at one’s disposal, it could be done by making use of methods that are made use of every day in the laboratory. Not many years ago that statement would have been challenged. The constituents of plants and animals were supposed to be entirely different from the constituents of the inanimate inorganic parts of the earth, and it was further supposed that those substances which are elaborated under the influence of the life-process cannot be formed without this influence. This may be true of the most complex constituents of plants and animals, but it is certainly not true of some of the simpler of these constituents. For example, urea, one of the most characteristic substances formed in the animal body, was made in the laboratory in 1828, by a method which was entirely independent of the life-process; and since that time innumerable other substances which are characteristic products of the life-process have been made artificially. So that, as we know very well what fats are, and can make substances of the same kind in the laboratory, there is nothing out of the way in saying that the fats could probably be made artificially. Let us assume that they can be. What then?
Next in order of complexity come the so-called carbohydrates, [p.140] which include the sugars, starch, and cellulose. Is it “highly probable” that the chemist can build these up out of the elements in the laboratory? Thanks to Emil Fischer, of Berlin, we can now almost say that sugar is not an unsolved problem. Within the last few years more has been done to clear up the problem of the sugars than in all preceding time put together. One of the simplest sugars has been prepared artificially in the laboratory, and the relations between the others have been, to a large extent, revealed.
But the sugars are simple things compared with starch. Starch is an unsolved problem. It is of the highest importance in Nature. Its wide distribution among plants and the part that it plays as a constituent of foods show this. What is it? Of course, if we say it is a carbohydrate, we have made the whole subject clear! The truth is we know very little about it, in spite of the large amount of work that has been done on it. In what has been done there is little promise of success, though the chemical optimist hopes, even in the face of starch. I confess to being a moderate optimist. If asked why I hope in this case, I could only answer, “ I hope—that is all.”
Let us take the next step. This brings us to cellulose, a substance of very great importance for all plants. It forms, as it were, their skeletons. Just as animals are built upon a basis of bone, so plants are built upon a basis of cellulose. It is that constituent of plants that gives them form and that enables them to resist the disintegrating influences to which they are subject in Nature. When a piece of wood is treated with certain active substances, “chemicals” as they are called by the outside world, many of the constituents are destroyed and removed, and, finally, what is known as wood-pulp remains. This is mainly cellulose. As is well known, large quantities of paper are made from this pulp. Paper is, in fact, more or less pure cellulose. Every plant contains cellulose, and without it the plants could not exist. It seems as though a chemist ought to feel humiliated to have to confess that even less is known about cellulose than about starch. There appears to be some reason for believing that it is distantly related to starch, but that is about all we can say. It is probably enormously complicated. To be sure, it contains only the three elements, carbon, hydrogen, and oxygen, but these three elements can combine with [p.141] one another in thousands of different ways, forming, on the one hand, relatively simple products, and, on the other, products of such complexity that before them the chemist can only stand and wonder. Cellulose belongs to the latter class.
THE AWESOME PROTEIDS
FINALLY, let us remove our hats and shoes, and, bowing low, ask with bated breath: — What about the proteids? What about them, indeed? Let us, rather, go back to cellulose and starch and recover our courage and our heads. This atmosphere is stifling. I always feel like running away when any one begins to talk about proteids in my presence, and here I am, trying to write something about them. I ought to be ashamed of myself. Quoting from a text-book of physiology: “These (proteids) form the principal solids of the muscular, nervous, and glandular tissues, of the serum of blood, of serous fluids, and of lymph.” That tells the story. What could we do without them? It is not for me to say what we know about proteids. In my youth I had a desire to attack these dragons, but now I am afraid of them. Fortunately, there is no occasion here for enlarging upon them. I only want to make clear the fact that they are unsolved problems of chemistry; and, let me add, they are likely to remain such for generations to come. Yet every one who knows anything about chemistry and physiology knows that these proteids must be understood, before we can hope to have a clear conception of the chemical processes of the human body. Fortunately for us, there are always some chemists who delight in working upon the most difficult problems and are not willing to take “ No” for an answer. So that there is always some one working on the proteids, and something is coming of it.
In the field of synthetic chemistry perhaps the most important problem among those that are unsolved is that presented by protoplasm. I have recently heard of a school, and a primary school at that, where the small children are introduced to the mysteries of life by being told “all about” protoplasm. If I were a pupil in that school, I might be able to tell my readers what protoplasm is, but, as I have not that privilege, I shall have to acknowledge that I know very little about it. In fact, it is a substance, or a mixture of substances, with which the chemist can do very little. Great interest has been taken in all that pertains to protoplasm, because it is so directly connected with life. The simplest organisms are the amœba.These may [p.142] be regarded as representing life reduced to its lowest form. Now an amœba “ is wholly, or almost wholly protoplasm.” “It lives, moves, eats, grows, and, after a time, dies, having been, during its whole life, hardly anything more than a minute lump of protoplasm”—(Foster). Regarded as a chemical substance, it contains the elements oxygen, hydrogen, nitrogen, carbon, and sulphur in fairly constant proportions. It would be a great day for chemistry if a chemist should succeed in putting together, and causing to unite, the above-named elements in the proportions in which they are present in protoplasm, and he should find that he had made protoplasm artificially. If this artificial protoplasm should move and eat and grow, he would deserve to be ranked with Pygmalion of old. What are the prospects?
In the first place, protoplasm does not appear to be a single substance, but a mixture of substances. It contains something that is derived from a proteid, something else derived from a fat, and still a third something derived from a carbohydrate. Perhaps these three things are chemically united with one another, and not simply mixed. The problem presented to the chemist is one of the greatest difficulty. It would be necessary for him to determine exactly what proteid, what fat, and what carbohydrate are essential to the existence of protoplasm; then to bring these together, and show that the substance thus obtained is identical with protoplasm. This might be accomplished, and yet the protoplasm obtained not be a living thing; for there is dead, as well as living, protoplasm. There is no evidence that any chemist is engaged in attempts to make protoplasm in the laboratory. Possibly some are dreaming of this problem, but dreams are generally harmless, and sometimes they are pleasant, and, indeed, useful. Before we can understand, if we ever are to understand, the difference between a living and a dead tissue, we must understand what protoplasm is, and our chances of solving the problem presented by this important basis of life are extremely poor. Still, we may hope to get nearer its solution by continued investigation, and we shall have to be satisfied with small returns for our labor.
Chemistry has to deal with the composition of things, and the changes in the composition of things, and all that pertains to these subjects. Changes in composition are often brought [p.143] about by raising the temperature. To take a comparatively simple, though not a familiar, example, water is a compound of the elements of hydrogen and oxygen. When this is heated, it is converted into water-vapor. When this vapor is heated to 4,500 degrees Fahrenheit, it is resolved into hydrogen and oxygen. At this temperature the compound, water, cannot exist. On the other hand, when hydrogen and oxygen are brought together at ordinary temperatures, they do not combine to form water, unless a spark or a flame is brought in contact with the mixture, when a violent explosion occurs, and this is the signal of the chemical union of the two elements to form water. Again, when wood is heated, it gives off gases and liquids, and at last there is nothing left but charcoal, which is one form of the element carbon. It is plain that some substances, that can exist at ordinary temperature, are decomposed—that is to say, they cannot exist—at high temperatures. This is, in fact, true of many of the substances familiar to us. But heat not only decomposes compounds; it also, if not too intense, causes elements to combine to form compounds. In the laboratory and in the factory heat is constantly being employed for the purpose of bringing about, or aiding, chemical action. The blast-furnace, from which comes all our iron, is a good example. The object in view is the separation of the metal, iron, from its ores. The ores consist of iron in combination with oxygen and, sometimes, other things; but it is the oxygen that gives the principal difficulty. When the compound of iron and oxygen is heated with something that, under the circumstances, has the power to combine with the oxygen and escape with it in the form of a gas, the iron is left behind. Charcoal or coke is used for this purpose. At high temperatures, these substances, which are different forms of the element carbon, take the oxygen from the iron, and the metal liberated sinks to the bottom of the furnace in the molten state, while the gaseous compound of carbon and oxygen passes out of the top of the furnace. The oxygen changes partners. It is to be observed that the iron ore might be mixed with the charcoal, and the mixture allowed to stand at ordinary temperatures for any length of time, without separation of iron. Heat is necessary, and a good deal of it, to cause the charcoal to unite with the oxygen and carry it off into space.
[p.144] Heat being an important factor in chemical acts, the question suggests itself: What will be the effect upon chemical processes if the temperature is raised much above the range within which we ordinarily work? And at the same time the complementary question will suggest itself: What will be the effect of lowering the temperature much below that at which we ordinarily work?
EXTREMES OF TEMPERATURE
UNTIL within the last few years the highest temperatures attainable were reached by the aid of the so-called compound blowpipe, which is an instrument for burning hydrogen, or some other combustible gas, in oxygen under pressure. By the aid of this instrument platinum was melted and, in one case, silver was boiled. But now the introduction of powerful electric currents has made the production of much higher temperatures possible, and marvelous results have been reached. M. Moissan, of Paris, has for some time been engaged in studying the chemical effects of high temperatures, and to him we owe almost all we know of chemistry at these temperatures. He has made use of a simple contrivance, which he calls an electric furnace. In this he has subjected many things to temperatures as high as from 6,000 to 7,000 degrees Fahrenheit. It is a pity that Dante could not have taken a course in chemistry under M. Moissan. These temperatures, notwithstanding their great height, are suggestive of the lower regions. This work has opened up a new world to chemists, and has shown them that there are many unsolved problems to be found here. Things that unite readily at ordinary high temperatures do not act at all at these higher temperatures; and things that do not act at all at the former act vigorously at the latter. There is no end of what may be learned in this new field.
Just as it is desirable to know how things act upon one another at high temperatures, so it is equally desirable to know how they act at low temperatures. Curiously enough, work in this direction has kept pace with that in the opposite direction, referred to in the last paragraph. Within the last year or two, the attention of everybody has been directed to low temperatures by the interesting work that has been done on liquid air. It is well known that air can now be liquefied on the large scale, and that liquid air is an article of commerce. This brings low temperatures to our door, for it is only necessary to expose the liquid in an open vessel to produce a temperature of about 300 [p.145] degrees below zero, Fahrenheit! Then, further, Dewar has recently succeeded in liquefying and, indeed, solidifying hydrogen—a much more difficult feat than liquefying air—and with the solid thus produced he has readied the temperature 432 degrees below zero, Fahrenheit! There is no serious difficulty then, at present, in studying chemical action at temperatures in the neighborhood of 300 degrees below zero. The first results are not reassuring. Things are not very lively down there, to say the least. It may be that all chemical action ceases below a certain temperature, but we do not, as yet, know enough about this subject to justify us in speaking with confidence about it. Countless experiments yet unborn will have to be tried. In thinking of the possibilities, we are confronted with what appears to be a paradox. It has been pointed out that high temperature, in many cases, has the effect of decomposing substances. This shows that these substances are more stable at low temperatures than at the ordinary temperatures. In other words, if heat causes the constituents to separate, cold might apparently cause them to unite more firmly. But, if this is so, why do not substances act upon each other readily at low temperatures? It may be that the constituents are so firmly held together that they cannot move about among one another, as they must in order to combine. The water that is frozen in a glacier does not act like water at ordinary temperatures. It is, as it were, chained up and prevented from obeying the laws of water.
THE GREAT UNSOLVED
IN what I have thus far had to say, I have kept in view certain problems which do not necessarily call for much speculation. It would, however, hardly be fair to leave the speculative side of chemistry entirely out of consideration. Sometimes young pupils are introduced to chemistry through the atom. Only very young, or very ignorant, persons can talk with confidence about atoms. The further one goes into the mysteries of chemistry, the more mysterious appears the atom. In fact, the atom is the great unsolved problem of chemistry. But this is subtle. What is an atom? Ah! that is the question. It has been a favorite subject of thought from the earliest days. Up to the beginning of this century, however, it was nothing but a metaphysical plaything. The wits of generations of philosophers have been sharpened by efforts to decide whether matter is infinitely divisible or not. Take a piece of, say, iron. No [p.146] matter what its size may be, it can be broken up into smaller pieces; and each of the pieces thus obtained can be still further subdivided. Now, how far can this process of subdivision be carried? Is there any limit? The atomists held that, after a time, particles would be reached so small that they could not be made smaller. But their opponents said, “No! this is inconceivable. Matter must be infinitely divisible.” As neither side could prove the other wrong, the question under discussion was well adapted to the purposes of controversy.
The atom of to-day is a scientific abstraction. Many facts have been brought to light that make it appear certain that matter is not continuous—is not capable of infinite subdivision. Dalton, the Quaker schoolmaster of Manchester, was the first one to bring the atom down to the earth and make it a useful idea. How he did this cannot be shown here. Suffice it to say, the atomic theory proposed by Dalton in the early years of this century lives to-day, and is stronger than it has ever been, notwithstanding the efforts that have been made to show that it is built upon sand. It has been, and is to-day, an extremely useful theory. Whether it will always continue to be so is another question, and one that need not bother us. It is believed that each elementary substance—that is to say, each chemical element—consists of minute particles that are not broken up in the course of chemical changes. These particles that remain intact are the atoms of chemistry. Some such theory is absolutely necessary to account for the fundamental laws of chemistry.
Into what thin air we enter, when we begin to speak of the properties of the individual atom, will appear when it is stated that, according to the calculations of Lord Kelvin, the molecule of hydrogen, which is at least twice as large as its atom, is of such size that it would take 50,000,000 of them placed in a row to occupy an inch! To be sure, most atoms are larger than those of hydrogen, but there are few so large that it would not be necessary to have about a million of them to occupy an inch. What sense is there in talking about such things? We shall never be able to see them, or to prove that they exist. True, but the conception of the atom has been of great help to chemists, and, as long as it continues to be helpful, it will be clung to.
[p.147] If the views held by the majority of chemists are true, the science of chemistry is the science of atoms. The astronomer has to deal with infinite distances and the largest masses in the universe. The chemist, on the other hand, has to deal with the shortest distances and the minutest particles of matter. The astronomer uses the telescope, but there is no microscope that can carry us to the atom. The astronomer observes points of light, follows their motions, and works out the laws that govern them. The chemist has troubles of another kind. He cannot deal directly with single atoms. No matter how small a quantity of an element he may use in his experiment, he has to deal with a large number of atoms. Every time he performs an experiment millions of atoms come into play. He studies his substances before action and after action. New substances are formed, and he concludes the atoms have arranged themselves in different ways. What he knows is that new substances with new properties are formed. He knows this whether atoms are realities or not, but the atom helps him to form a picture of what probably takes place throughout the masses with which he is dealing. The atoms are as far removed from the intellectual gaze of the chemist as the most remote stars from the eye of the astronomer.
Yet the chemist talks about the way in which atoms are combined with one another; and he draws figures, and constructs models to show it all. And he doesn’t do this for his amusement, but because he is helped by it. He talks in the language of chemistry, as the mathematician talks in the language of mathematics. Some day he will, no doubt, understand the language better. Probably the language itself will be changed, and that which he now uses will seem like the prattle of an infant.
One other side of chemistry must be turned into view before I can close. I am not sure that I can make myself intelligible in what I still have to say, but I shall try. Thus far, in what has been said about chemical acts, the material side has been kept in view. The relations between the elements; the artificial preparation of the substances that enter into the composition of living things; the changes in the composition of matter at high and at low temperatures; and, finally, the atom—these are the subjects dealt with. But, whenever a chemical act takes place, there are changes in the temperature and in the electrical [p.148] condition of the substances involves, in addition to the changes in composition. It is while in action that chemical substances are most interesting. Generally we have to content ourselves with observations before and after an act, but we should learn a great deal more about the nature of the act, if we could make observations while it is in progress. We should find it very difficult, if not impossible, to learn the law of falling bodies, if we could only observe bodies before and after they have fallen; but by observing them in the act of falling we can, without difficulty, deduce the law.
LAWS OF CHEMICAL CHANGE
GENERALLY speaking, chemical acts are so rapid that it is impossible to make observations during their course. Much progress has been made in this field during the past fifteen or twenty years, and some of the great laws of chemical action have been discovered. What has been learned is, however, only enough to whet the appetite of chemists. To illustrate in another way what is meant by making observations during a chemical act, let us take the case of gunpowder. This usually consists of charcoal, sulphur, and saltpeter. A spark is sufficient to cause the chemical act that is accompanied by the explosion. We can collect everything that is formed, and show what changes in composition have taken place. But we should like to know something about the act itself, and yet, plainly, observations during the act cannot be numerous, or especially instructive. And so it is with most common chemical changes that are studied in the laboratory. We get only snap-shots at them. If we could only get a series of pictures at short intervals, we might, by combining these afterward, get some idea of what is taking place during the act. Fortunately, there are ways of controlling certain classes of chemical acts and reducing their speed, so that observations can be made during their progress; and. much has been learned in this way. Here is a great field for further study, and it presents many unsolved problems.
Finally, a few words about water. It is said that a well-known chemist some years ago made a bet that a certain company of chemists could not name a chemical subject that would not, in turn, suggest to him a profitable chemical investigation. Thereupon, after much deliberation, the challenged company suggested “water,” on the assumption that this has been thoroughly worked over, and does not present unsolved problems. The result was a beautiful investigation of some of the properties of water. Every one knows that water is the most abundant substance on the earth. It also plays a more important part in the changes that are taking place on the earth than any other substance. We are only beginning to learn how it acts. That it dissolves many things is well known, but let us not be misled because this phenomenon is so common and so familiar. Put a little salt in water. What becomes of it? It disappears. There is no solid substance in the vessel. We may bandy phrases as we please, but we cannot tell what has become of the salt. We can get the salt out of the water by boiling the solution and letting the water pass off as steam, when the salt will be left behind. As we put the salt in and take it out, we have been accustomed until recently to think of the salt as being present in the solution as such. One of the most important advances in chemistry made of late years is that which leads to the conception that, in dilute solutions at least, there is little, if any, salt present; that, in some way, the water decomposes it into particles highly charged with electricity. These particles are called ions. This idea has thrown a great deal of light upon important problems of chemistry, but it has suggested many new ones. Some substances—for example, sugar—do not act like salt when dissolved in water. Why this difference? Then, too, some liquids which are good solvents do not act at all like water. What is it in water that distinguishes it from most other liquids, such as alcohol and ether, enabling it to tear many substances asunder? These are questions that are now very much to the front. Rapid progress is being made, and we may look for important discoveries in this field in the near future.
- Science Quotes by Ira Remsen.
- 10 Feb - short biography, births, deaths and events on date of Remsen's birth.
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