The Story of Alchemy and the Beginnings of Chemistry Part 11

Radium compounds spontaneously give off energy in the form of heat. A quant.i.ty of radium chloride which contains 1 gram of radium continuously gives out, per hour, a quant.i.ty of heat sufficient to raise the temperature of 1 gram of water through 100 C., or 100 grams of water through 1 C. The heat given out by 1 gram of radium during twenty-four hours would raise the temperature of 2400 grams of water through 1 C.; in one year the temperature of 876,000 grams of water would be raised through 1 C.; and in 1800 years, which is approximately the half-life period of radium, the temperature of 1,576,800 _kilograms_ of water would be raised through 1 C. These results may be expressed by saying that if 1 gram (about 15 grains) of radium were kept until half of it had changed into inactive substances, and if the heat spontaneously produced during the changes which occurred were caused to act on water, that quant.i.ty of heat would raise the temperature of about 15 tons of water from its freezing- to its boiling-point.

Radium compounds send forth three kinds of rays, distinguished as _alpha_, _beta_, and _gamma_ rays. Experiments have made it extremely probable that the [alpha]-rays are streams of very minute particles, somewhat heavier than atoms of hydrogen, moving at the rate of about 18,000 miles per second; and that the [beta]-rays are streams of much more minute particles, the ma.s.s of each of which is about one one-thousandth of the ma.s.s of an atom of hydrogen, moving about ten times more rapidly than the [alpha]-particles, that is, moving at the rate of about 180,000 miles per second. The [gamma]-rays are probably pulsations of the ether, the medium supposed to fill s.p.a.ce. The emission of [alpha]-rays by radium is accompanied by the production of the inert elementary gas, helium; therefore, the [alpha]-rays are, or quickly change into, rapidly moving particles of helium. The particles which const.i.tute the [beta]-rays carry electric charges; these electrified particles, each approximately a thousand times lighter than an atom of hydrogen, moving nearly as rapidly as the pulsations of the ether which we call light, are named _electrons_. The rays from radium compounds discharge electrified bodies, ionise gases, that is, cause them to conduct electricity, act on photographic plates, and produce profound changes in living organisms.

The radium emanation is a gas about 111 times heavier than hydrogen; to this gas Sir William Ramsay has given the name _niton_. The gas has been condensed to a colourless liquid, and frozen to an opaque solid which glows like a minute arc-light. Radium emanation gives off [alpha]-particles, that is, very rapidly moving atoms of helium, and deposits exceedingly minute quant.i.ties of a solid, radio-active substance known as radium A. The change of the emanation into helium and radium A proceeds fairly rapidly: the half-life period of the emanation is a little less than four days. This change is attended by the liberation of much energy.

The only satisfactory mental picture which the facts allow us to form, at present, of the emission of [beta]-rays from radium compounds is that which represents these rays as streams of electrons, that is, particles, each about a thousand times lighter than an atom of hydrogen, each carrying an electric charge, and moving at the rate of about 180,000 miles per second, that is, nearly as rapidly as light.

When an electric discharge is pa.s.sed from a plate of metal, arranged as the kathode, to a metallic wire arranged as the anode, both sealed through the walls of a gla.s.s tube or bulb from which almost the whole of the air has been extracted, rays proceed from the kathode, in a direction at right angles thereto, and, striking the gla.s.s in the neighbourhood of the anode, produce a green phosph.o.r.escence. Facts have been gradually acc.u.mulated which force us to think of these _kathode rays_ as streams of very rapidly moving electrons, that is, as streams of extraordinarily minute electrically charged particles identical with the particles which form the [beta]-rays emitted by compounds of radium.

The phenomena of radio-activity, and also the phenomena of the kathode rays, have obliged us to refine our machinery of minute particles by including therein particles at least a thousand times lighter than atoms of hydrogen. The term _electron_ was suggested, a good many years ago, by Dr Johnstone Stoney, for the unit charge of electricity which is carried by an atom of hydrogen when hydrogen atoms move in a liquid or gas under the directing influence of the electric current.

Some chemists speak of the electrons, which are the [beta]-rays from radium, and the kathode rays produced in almost vacuous tubes, as non-material particles of electricity. Non-material means devoid of ma.s.s. The method by which approximate determinations have been made of the charges on electrons consists in measuring the ratio between the charges and the ma.s.ses of these particles. If the results of the determinations are accepted, electrons are not devoid of ma.s.s.

Electrons must be thought of as material particles differing from other minute material particles in the extraordinary smallness of their ma.s.ses, in the ident.i.ty of their properties, including their ma.s.s, in their always carrying electric charges, and in the vast velocity of their motion. We must think of an electron either as a unit charge of electricity one property of which is its minute ma.s.s, or as a material particle having an extremely small ma.s.s and carrying a unit charge of electricity: the two mental pictures are almost, if not quite, identical.

Electrons are produced by sending an electric discharge through a gla.s.s bulb containing a minute quant.i.ty of air or other gas, using metallic plates or wires as kathode and anode. Experiments have shown that the electrons are identical in all their properties, whatever metal is used to form the kathode and anode, and of whatever gas there is a minute quant.i.ty in the bulb. The conclusion must be drawn that identical electrons are const.i.tuents of, or are produced from, very different kinds of chemical elements. As the facts about kathode rays, and the facts of radio-activity are (at present) inexplicable except on the supposition that these phenomena are exhibited by particles of extraordinary minuteness, and as the smallest particles with which chemists are concerned in their everyday work are the atoms of the elements, we seem obliged to think of many kinds of atoms as structures, not as h.o.m.ogeneous bodies. We seem obliged to think of atoms as very minute material particles, which either normally are, or under definite conditions may be, a.s.sociated with electrically charged particles very much lighter than themselves, all of which are identical, whatever be the atoms with which they are a.s.sociated or from which they are produced.

In their study of different kinds of matter, chemists have found it very helpful to place in one cla.s.s those substances which they have not been able to separate into unlike parts. They have distinguished this cla.s.s of substances from other substances, and have named them _elements_. The expression _chemical elements_ is merely a summary of certain observed facts. For many centuries chemists have worked with a conceptual machinery based on the notion that matter has a grained structure. For more than a hundred years they have been accustomed to think of atoms as the ultimate particles with which they have had to deal. Working with this order-producing instrument, they have regarded the properties of elements as properties of the atoms, or of groups of a few of the atoms, of these substances. That they might think clearly and suggestively about the properties of elements, and connect these with other chemical facts, they have translated the language of sense-perceptions into the language of thought, and, for _properties of those substances which have not been decomposed_, have used the more fertile expression _atomic properties_. When a chemist thinks of an atom, he thinks of the minutest particle of one of the substances which have the cla.s.s-mark _have-not-been-decomposed_, and the cla.s.s-name _element_. The chemist does not call these substances elements because he has been forced to regard the minute particles of them as undivided, much less because he thinks of these particles as indivisible; his mental picture of their structure as an atomic structure formed itself from the fact that they had not been decomposed. The formation of the cla.s.s _element_ followed necessarily from observed facts, and has been justified by the usefulness of it as an instrument for forwarding accurate knowledge. The conception of the elementary atom as a particle which had not been decomposed followed from many observed facts besides those concerning elements, and has been justified by the usefulness of it as an instrument for forwarding accurate knowledge. Investigations proved radio-activity to be a property of the very minute particles of certain substances, and each radio-active substance to have characteristic properties, among which were certain of those that belong to elements, and to some extent are characteristic of elements. Evidently, the simplest way for a chemist to think about radio-activity was to think of it as an atomic property; hence, as atomic properties had always been regarded, in the last a.n.a.lysis, as properties of elements, it was natural to place the radio-active substances in the cla.s.s _elements_, provided that one forgot for the time that these substances have not the cla.s.s-mark _have-not-been-decomposed_.

As the facts of radio-activity led to the conclusion that some of the minute particles of radio-active substances are constantly disintegrating, and as these substances had been labelled _elements_, it seemed probable, or at least possible, that the other bodies which chemists have long called elements are not true elements, but are merely more stable collocations of particles than the substances which are cla.s.sed as compounds. As compounds can be changed into certain other compounds, although not into any other compounds, a way seemed to be opening which might lead to the transformation of some elements into some other elements.

The probability that one element might be changed into another was increased by the demonstration of the connexions between uranium and radium. The metal uranium has been cla.s.sed with the elements since it was isolated in 1840. In 1896, Becquerel found that compounds of uranium, and also the metal itself, are radio-active. In the light of what is now known about radio-activity, it is necessary to suppose that some of the minute particles of uranium emit particles lighter than themselves, and change into some substance, or substances, different from uranium; in other words, it is necessary to suppose that some particles of uranium are spontaneously disintegrating.

This supposition is confirmed by the fact, experimentally proved, that uranium emits [alpha]-rays, that is, atoms of helium, and produces a substance known as uranium X. Uranium X is itself radio-active; it emits [beta]-rays, that is, it gives off electrons.

Inasmuch as all minerals which contain compounds of uranium contain compounds of radium also, it is probable that radium is one of the disintegration-products of uranium. The rate of decay of radium may be roughly expressed by saying that, if a quant.i.ty of radium were kept for ten thousand years, only about one per cent. of the original quant.i.ty would then remain unchanged. Even if it were a.s.sumed that at a remote time the earth's crust contained considerable quant.i.ties of radium compounds, it is certain that they would have completely disappeared long ago, had not compounds of radium been reproduced from other materials. Again, the most likely hypothesis is that compounds of radium are being produced from compounds of uranium.

Uranium is a substance which, after being rightly cla.s.sed with the elements for more than half a century, because it had not been separated into unlike parts, must now be cla.s.sed with the radium-like substances which disintegrate spontaneously, although it differs from other radio-active substances in that its rate of change is almost infinitively slower than that of any of them, except thorium.[12]

Thorium, a very rare metal, is the second of the seventy-five or eighty elements known when radio-activity was discovered, which has been found to undergo spontaneous disintegration with the emission of rays. The rate of change of thorium is considerably slower than that of uranium.[13] None of the other substances placed in the cla.s.s of elements is radio-active.

[12] The life-period of uranium is probably about eight thousand million years.

[13] The life-period of thorium is possibly about forty thousand million years.

On p. 192 I said, that when the radio-active substances had been labelled _elements_, the facts of radio-activity led some chemists to the conclusion that the other bodies which had for long been called by this cla.s.s-name, or at any rate some of these bodies, are perhaps not true elements, but are merely more stable collocations of particles than the substances called compounds. It seems to me that this reasoning rests on an unscientific use of the term _element_; it rests on giving to that cla.s.s-name the meaning, _substances a.s.serted to be undecomposable_. A line of demarcation is drawn between _elements_, meaning thereby forms of matter said to be undecomposable but probably capable of separation into unlike parts, and _true elements_, meaning thereby groups of identical undecomposable particles. If one names the radio-active substances _elements_, one is placing in this cla.s.s substances which are specially characterised by a property the direct opposite of that the possession of which by other substances was the reason for the formation of the cla.s.s. To do this may be ingenious; it is certainly not scientific.

Since the time of Lavoisier, since the last decade of the eighteenth century, careful chemists have meant by an element a substance which has not been separated into unlike parts, and they have not meant more than that. The term _element_ has been used by accurate thinkers as a useful cla.s.s-mark which connotes a property--the property of not having been decomposed--common to all substances placed in the cla.s.s, and differentiating them from all other substances. Whenever chemists have thought of elements as the ultimate kinds of matter with which the physical world is constructed--and they have occasionally so thought and written--they have fallen into quagmires of confusion.

Of course, the elements may, some day, be separated into unlike parts.

The facts of radio-activity certainly suggest some kind of inorganic evolution. Whether the elements are decomposed is to be determined by experimental inquiry, remembering always that no number of failures to simplify them will justify the a.s.sertion that they cannot be simplified. Chemistry neither a.s.serts or denies the decomposability of the elements. At present, we have to recognise the existence of extremely small quant.i.ties, widely distributed in rocks and waters, of some thirty substances, the minute particles of which are constantly emitting streams of more minute, identical particles that carry with them very large quant.i.ties of energy, all of which thirty substances are characterised, and are differentiated from all other cla.s.ses of substances wherewith chemistry is concerned, by their spontaneous mutability, and each is characterised by its special rate of change and by the nature of the products of its mutations. We have now to think of the minute particles of two of the seventy-five or eighty substances which until the other day had not been decomposed, and were therefore justly called elements, as very slowly emitting streams of minuter particles and producing characteristic products of their disintegration. And we have to think of some eighty substances as particular kinds of matter, at present properly called elements, because they are characterised, and differentiated from all other substances, by the fact that none of them has been separated into unlike parts.

The study of radio-activity has introduced into chemistry and physics a new order of minute particles. Dalton made the atom a beacon-light which revealed to chemists paths that led them to wider and more accurate knowledge. Avogadro illuminated chemical, and also physical, ways by his conception of the molecule as a stable, although separable, group of atoms with particular properties different from those of the atoms which const.i.tuted it. The work of many investigators has made the old paths clearer, and has shown to chemists and physicists ways they had not seen before, by forcing them to think of, and to make use of, a third kind of material particles that are endowed with the extraordinary property of radio-activity.

Dalton often said: "Thou knowest thou canst not cut an atom"; but the fact that he applied the term _atom_ to the small particles of compounds proves that he had escaped the danger of logically defining the atom, the danger of thinking of it as a particle which never can be cut. The molecule of Avogadro has always been a decomposable particle. The peculiarity of the new kind of particles, the particles of radio-active bodies, is, not that they can be separated into unlike parts by the action of external forces, but that they are constantly separating of their own accord into unlike parts, and that their spontaneous disintegration is accompanied by the production of energy, the quant.i.ty of which is enormous in comparison with the minuteness of the material specks which are the carriers of it.

The continued study of the properties of the minute particles of radio-active substances--a new name is needed for those most mutable of material grains--must lead to discoveries of great moment for chemistry and physics. That study has already thrown much light on the phenomena of electric conductivity; it has given us the electron, a particle at least a thousand times lighter than an atom of hydrogen; it has shown us that identical electrons are given off by, or are separated from, different kinds of elementary atoms, under definable conditions; it has revealed unlooked-for sources of energy; it has opened, and begun the elucidation of, a new department of physical science; it has suggested a new way of attacking the old problem of the alchemists, the problem of the trans.m.u.tation of the elements.

The minute particles of two of the substances for many years cla.s.sed as elements give off electrons; uranium and thorium are radio-active.

Electrons are produced by sending an electric discharge through very small traces of different gases, using electrodes of different metals.

Electrons are also produced by exposing various metals to the action of ultra-violet light, and by raising the temperature of various metals to incandescence. Electrons are always identical, whatever be their source. Three questions suggest themselves. Can the atoms of all the elements be caused to give off electrons? Are electrons normal const.i.tuents of all elementary atoms? Are elementary atoms collocations of electrons? These questions are included in the demand--Is it possible "to imagine a model which has in it the potentiality of explaining" radio-activity and other allied phenomena, as well as all other chemical and physical properties of elements and compounds? These questions are answerable by experimental investigation, and only by experimental investigation. If experimental inquiry leads to affirmative answers to the questions, we shall have to think of atoms as structures of particles much lighter than themselves; we shall have to think of the atoms of all kinds of substances, however much the substances differ chemically and physically, as collocations of identical particles; we shall have to think of the properties of atoms as conditioned, in our final a.n.a.lysis, by the number and the arrangement of their const.i.tutive electrons. Now, if a large probability were established in favour of the view that different atoms are collocations of different numbers of identical particles, or of equal numbers of differently arranged identical particles, we should have a guide which might lead to methods whereby one collocation of particles could be formed from another collocation of the same particles, a guide which might lead to methods whereby one element could be transformed into another element.

To attempt "to imagine a model which has in it the potentiality of explaining" radio-activity, the production of kathode rays, and the other chemical and physical properties of elements and compounds, might indeed seem to be a hopeless undertaking. A beginning has been made in the mental construction of such a model by Professor Sir J.J.

Thomson. To attempt a description of his reasoning and his results is beyond the scope of this book.[14]

[14] The subject is discussed in Sir J.J. Thomson's _Electricity and Matter_.

The facts that the emanation from radium compounds spontaneously gives off very large quant.i.ties of energy, and that the emanation can easily be brought into contact with substances on which it is desired to do work, suggested to Sir William Ramsay that the transformation of compounds of one element into compounds of another element might possibly be effected by enclosing a solution of a compound along with radium emanation in a sealed tube, and leaving the arrangement to itself. Under these conditions, the molecules of the compound would be constantly bombarded by a vast number of electrons shot forth at enormous velocities from the emanation. The notion was that the molecules of the compound would break down under the bombardment, and that the atoms so produced might be knocked into simpler groups of particles--in other words, changed into other atoms--by the terrific, silent shocks of the electrons fired at them incessantly by the disintegrating emanation. Sir William Ramsay regards his experimental results as establis.h.i.+ng a large probability in favour of the a.s.sertion that compounds of copper were transformed into compounds of lithium and sodium, and compounds of thorium, of cerium, and of certain other rare metals, into compounds of carbon. The experimental evidence in favour of this statement has not been accepted by chemists as conclusive. A way has, however, been opened which may lead to discoveries of great moment.

Let us suppose that the transformation of one element into another element or into other elements has been accomplished. Let us suppose that the conception of elementary atoms as very stable arrangements of many identical particles, from about a thousand to about a quarter of a million times lighter than the atoms, has been justified by crucial experiments. Let us suppose that the conception of the minute grains of radio-active substances as particular but constantly changing arrangements of the same identical particles, stable groups of which are the atoms of the elements, has been firmly established. One result of the establishment of the electronic conception of atomic structure would be an increase of our wonder at the complexity of nature's ways, and an increase of our wonder that it should be possible to subst.i.tute a simple, almost rigid, mechanical machinery for the ever-changing flow of experience, and, by the use of that mental mechanism, not only to explain very many phenomena of vast complexity, but also to predict occurrences of similar entanglement and to verify these predictions.

The results which have been obtained in the examination of radio-activity, of kathode rays, of spectra at different temperatures, and of phenomena allied to these, bring again into prominence the ancient problem of the structure of what we call matter. Is matter fundamentally h.o.m.ogeneous or heterogeneous? Chemistry studies the relations between the changes of composition and the changes of properties which happen simultaneously in material systems. The burning fire of wood, coal, or gas; the preparation of food to excite and to satisfy the appet.i.te; the change of minerals into the iron, steel, copper, bra.s.s, lead, tin, lighting burning and lubricating oils, dye-stuffs and drugs of commerce; the change of the skins, wool, and hair of animals, and of the seeds and fibres of plants, into clothing for human beings; the manufacture from rags, gra.s.s, or wood of a material fitted to receive and to preserve the symbols of human hopes, fears, aspirations, love and hate, pity and aversion; the strange and most delicate processes which, happening without cessation, in plants and animals and men, maintain that balanced equilibrium which we call life; and, when the silver cord is being loosed and the bowl broken at the cistern, the awful changes which herald the approach of death; not only the growing gra.s.s in midsummer meadows, not only the coming of autumn "in dyed garments, travelling in the glory of his apparel," but also the opening buds, the pleasant scents, the tender colours which stir our hearts in "the spring time, the only pretty ring time, when birds do sing, ding-a--dong-ding": these, and a thousand other changes have all their aspects which it is the business of the chemist to investigate. Confronted with so vast a mult.i.tude of never-ceasing changes, and bidden to find order there, if he can--bidden, rather compelled by that imperious command which forces the human mind to seek unity in variety, and, if need be, to create a cosmos from a chaos; no wonder that the early chemists jumped at the notion that there must be, that there is, some _One Thing_, some _Universal Essence_, which binds into an orderly whole the perplexing phenomena of nature, some _Water of Paradise_ which is for the healing of all disorder, some "Well at the World's End," a draught whereof shall bring peace and calm security.

The alchemists set forth on the quest. Their quest was barren. They made the great mistake of fas.h.i.+oning _The One Thing, The Essence, The Water of Paradise_, from their own imaginings of what nature ought to be. In their own likeness they created their goal, and the road to it.

If we are to understand nature, they cried, her ways must be simple; therefore, her ways are simple. Chemists are people of a humbler heart. Their reward has been greater than the alchemists dreamed. By selecting a few instances of material changes, and studying these with painful care, they have gradually elaborated a general conception of all those transformations wherein substances are produced unlike those by the interaction of which they are formed. That general conception is now both widening and becoming more definite. To-day, chemists see a way opening before them which they reasonably hope will lead them to a finer, a more far-reaching, a more suggestive, at once a more complex and a simpler conception of material changes than any of those which have guided them in the past.