But that is by the way. A generation ago men seem to have pretty well made up their minds that they knew all about atoms. They said that everything was made up of atoms, that the atoms could not be subdivided nor changed into anything else except temporarily by combination with other atoms, and that when these combinations were broken up the atoms remained just as before, quite unchanged. They believed that the atoms were unchangeable and everlasting. Professor Tyndall, in a famous address, referred to this in somewhat flowery language, telling his hearers that the atoms would be still the same when they and he had "melted into the infinite azure of the past," which a wag translated into the slang expression of the time, "till all is blue."

Now not very long after Professor Tyndall made this historic speech Professor Henri Becquerel, of Paris, was trying some experiments with phosph.o.r.escent materials, that is, materials which glow in the darkness.

In the course of these experiments he used some photographic plates upon which, to his surprise, he found marks which he thought ought not to have been there. Thinking at first that he had accidentally "fogged" his plates, as every photographer has done at some time or other, he tried his experiments again with special care but still he got the mysterious marks.

Those marks were caused by some of those "unchangeable and everlasting"

atoms deliberately and of their own accord blowing themselves to bits.

For the celebrated Frenchman was not content to let the matter of those mysterious marks rest: he wanted to know what caused them and he did not desist until he was on the track of the secret. It appeared after careful investigation that they were made by the action of something in some of the ore of the metal "uranium" which he had been using.

Moreover, this something evidently had the power of penetrating through the walls of the dark-slide to the plate within. Finally, it was tracked down to the uranium itself which was unquestionably proved to be giving off something in the nature of invisible light, or at all events invisible rays, of strange penetrative power. A little later it was observed that certain ores of uranium seemed to give off these rays more freely than would be accounted for by the amount of uranium present, from which fact it was inferred that there must be something else present in the ore capable of giving off the rays much more powerfully than uranium can. Madame Curie ultimately found out two such substances, one of which she called, after her native land, Polonium (for she is a Pole), and the other Radium. It is the latter which is responsible for by far the greater part of the rays formed.

The rays are invisible, but they affect a photographic plate in the same way that light does. They also make air into a conductor of electricity and if allowed to impinge upon a surface coated with a suitable substance they cause it to glow.

This spontaneous giving off of rays is now spoken of by the general term of "radio-activity," and it has grown into an important branch of science. A number of other substances have been found to exhibit the same peculiar ray-forming powers, notably Thorium, one of the components of the incandescent gas mantle by the prolonged application of a fragment of which to a photographic plate an impression can be obtained due to the rays.

What, then, are these rays? It is found that they are of three kinds, not that they vary from time to time, but that they can be sorted out into three different sorts of rays which are given off simultaneously all the time.

The first sort are stopped by a sheet of paper, the second pa.s.sing easily through a thick metal plate, while the third appear to be identical with X-rays.

For convenience the three sorts are termed Alpha, Beta and Gamma rays, respectively, after the first three letters of the Greek alphabet.

Further, the Alpha rays prove to be a torrent of tiny particles about the size of atoms, indeed if they be collected the gas Helium is obtained, so that evidently they are helium atoms, and since that is one of those substances whose molecules consist of a single atom each they are also molecules of helium. No doubt the reason why they are so easily stopped by a piece of paper is because being complete atoms they are large, huge indeed, compared with the particles which form the Beta rays, for they are apparently those same electrons which are found in the X-ray tube, and which are at least 2000 times smaller than the smallest atom.

When the electrons in the vacuum tube are suddenly brought to a standstill X-rays are given off and in like manner X-rays no doubt would be given off when they start on their journey, providing that they started suddenly enough. Hence it is the starting or sudden explosion-like ejection of the Beta particles which is believed to give rise to the Gamma rays.

The strength or intensity of the rays can be measured very conveniently by their action in making air conductive to electricity, for which purpose a very beautiful but simple instrument called an Electroscope is employed. It consists generally of a gla.s.s-sided box or else a bottle with a large stopper, consisting of sulphur or some other particularly good insulator. Through this a wire pa.s.ses down into the inside of the vessel terminating in a vertical flat strip to the upper end of which is attached a similar strip of gold leaf or aluminium foil. Normally the leaf hangs down close to the strip, but if the wire above the stopper be electrified by touching it with a piece of sealing-wax rubbed lightly against the coat sleeve the charge of electricity pa.s.ses down into the inside and causes both strip and leaf to become so electrified that they repel each other.

Owing to the non-conductivity of the air in its normal condition the leaf will, if the insulation of the stopper be good, remain projecting almost horizontally for some time until, as it loses its charge by a slow leakage, it gradually settles down close to the strip.

If, however, a piece of radium be brought near while it is sticking out, the leaf will fall almost instantly. X-rays have a similar effect even from several feet or yards away.

The intensity of the radio-activity of different substances can be compared by noting the difference in the rate at which the leaf falls under the influence of each.

What is happening, then, to the atoms of radium, which causes them to show these curious effects and to give off these strange rays? To give any intelligent answer to that question we are bound to a.s.sume that which the older generation of scientists thought impossible, namely, that atoms can be broken up. Then we are forced to believe that the atoms of this particular substance radium are of a peculiarly flimsy unstable sort, so that they cannot permanently hold their parts together but are liable to break up, as far as we can see through their own inherent weakness and under the influence of disruptive forces at work within themselves.

We must remember, however, that the tiniest speck of matter which we can see contains a number of atoms of such a size as to be quite beyond the grasp of our minds. To give a rough idea of it in figures is useless as no one can comprehend the real value of a figure or two followed by probably from a dozen to twenty "noughts." It is best to content ourselves with the general statement that a speck of matter only just visible to the eye contains an exceedingly vast number of atoms. Of course a speck of radium is no exception to this and we must remember, too, that all of them do not break up at once. Indeed, the number breaking up at any time are actually countable by means of a very simple contrivance and a sensitive electrometer. Consequently, in view of the enormous number present and the comparatively small number breaking up at any moment, it is not surprising to hear that, so it is estimated, the process can go on for an almost indefinite number of years, certainly for hundreds. There are, moreover, certain facts which we need not go into here from which the above fact can be clearly inferred, quite apart from what has been said about the vast numbers of the atoms.

It seems as if the uranium atoms break up first, giving off helium atoms and electrons and leaving an intermediate substance called Ionium which in its turn breaks up giving off the same things again and leaving radium. That in its turn goes through a complicated series of changes still giving off the same alpha particles or atoms of helium and electrons until, it is suggested, it finally settles down into the simple commonplace metal lead of which we make bullets and water pipes and such-like ordinary things.

We see then that all through its history--its radio-active history at any rate--this stuff is throwing off atoms of helium at a very high velocity (about 50,000 miles a second), and if it be enclosed in anything this enclosing vessel or substance will be subjected to a continual bombardment by the alpha particles. Now just as a piece of iron gets hot if we hammer it, so the enclosing matter is heated by the continual blows which it is receiving night and day, year in and year out, from the alpha particles.

Consequently the immediate surroundings of a speck of radium are always slightly raised in temperature.

Moreover, if a speck of radium be placed against a screen covered with suitable materials each particle which strikes it will make a little splash of light. At least that is what it looks like when seen through a magnifying gla.s.s, but to the naked eye there only appears a beautiful steady glow.

Suppose, then, that instead of putting the speck of radiant matter in front of a screen we mix it up intimately with a fluorescent substance such as sulphide of zinc, we then get the same conditions in a slightly different form. Each particle of the substance serves as a tiny screen which glows every time a particle hits it. Thus is produced a luminous paint which glows by night, suitable for painting the dials of instruments which have to be used in the dark.

No doubt some of my readers will have experienced the strangely mingled delight and horror of seeing a Zeppelin in the night sky intent on dropping murder and death on the sleeping civilians of a peaceful town or city. Some too may have witnessed the later acts in that wonderful drama, when, beside the silvery monster illuminated by the beams of the searchlight there must have been, though quite invisible, a little aeroplane manned by one man or at most two. That aeroplane was, no doubt, fitted with instruments at which the pilot glanced now and then and which he was able to see and read because of the tiny speck of radium mixed into the paint. The little alpha particles gave him the light by which to see, but they gave no help to the Germans on the Zeppelin. Hence, in due time he did his work and the gigantic balloon, the pride of the Kaiser and his hordes, fell to the ground, a blazing wreck. How he did it I cannot tell, but of this I am sure, that most probably radium helped him by making luminous and visible the instruments which guided him.

But probably it has rendered and will still render us even greater services in the way of helping to repair the damages to our injured manhood. How many men came back from the war crippled with rheumatism because of the hardships through which they went. That disease is believed to be due to a substance which mingles with the blood and which, although usually liquid and harmless sometimes changes into a solid and settles in the joints. Now it is believed that radium properly administered will act upon that solid and cause it to change back into its liquid form again, thereby curing the disease. Certainly many of the mineral springs at such places as Bath and Buxton give forth a water which shows a certain amount of radio-activity and it may be that which gives those waters their healing properties. If so, we may look forward with confidence to the time when radio-activity will be induced to play a still more successful part in meeting this painful and widespread illness.

Then, of the other ills which will inevitably arise in our men through the hardships which they have endured are sure to be some of the cancerous type, many of which appear to succ.u.mb to treatment by radium.

If a very small quant.i.ty indeed be carried for a few days in a pocket it will imprint itself upon the skin beneath as if it burnt the tissues. It is never advisable, therefore, to carry radium in the pocket without special precautions. One cannot help feeling, however, that in that little fact is a hint of usefulness when the best modes of application have been discovered, for as a means of safely and painlessly burning away some undesirable growth it would seem to be without a rival. It is said, too, that it has the strange power of discriminating between the normal and the abnormal, attacking the latter but leaving the former, so that when applied, say, to some abnormal growth like cancer it may be able to remove it without harmful effect upon the surrounding tissues.

Of this, however, it is too soon to write with confidence. It has not been known long enough for our doctors to find out the best modes of use, but that will come with time: meanwhile there are indications that in all probability it will render good service to mankind.

CHAPTER IV

A GOOD SERVANT, THOUGH A BAD MASTER

One morning during the war the whole British nation was startled to learn that Mr. Lloyd George, then the Minister of Munitions, had taken over a large number of distilleries. Could it be that he, a teetotaller and temperance advocate, was going to supply all his workers with whiskey? Or was he going to close the places so as to stop the supply of that tempting drink?

Neither of these suggestions was his real reason. What he wanted the distilleries for was to make alcohol for the war, not for drinking purposes but for the very many uses which only alcohol can fulfil in most important manufactures.

Probably alcohol is the next important liquid to water. For example, certain parts of sh.e.l.ls have to be varnished and the only satisfactory way to make varnish is to dissolve certain gums in alcohol. The spirit makes the solid gum for the time being into a liquid which we can spread with a brush, yet, after being spread, it evaporates and pa.s.ses off into the air, leaving behind a beautiful coating of gum. That is how all varnishing is done, the alcohol forming the vehicle in which the solid gum is for the moment carried and by which it is applied. It is far and away the most suitable liquid for the purpose, and without it varnishing would be very difficult and unsatisfactory. Hence one need for alcohol, to carry on the war.

Then again some of the most important explosives are solid or semi-solid, and yet they require to be mixed in order to form the various "powders" in use by our gunners. The best way to bring about this mixture is to dissolve the two components in alcohol, thereby forming them both into liquids which can be readily mixed. Afterwards the alcohol evaporates; indeed, one of its great virtues for this and similar purposes is that it quietly takes itself off when it has done its work like a very well-drilled servant.

What then is this precious liquid and how is it produced? In order to answer that question it is necessary first to state that there are a whole family of substances called "alcohols," all of which are composed of carbon, hydrogen and oxygen in certain proportions. There are also a number of kindred substances also, not exactly brothers but first cousins, so to speak, which because of their resemblance to this important family have names terminating in "ol."

They owe their existence to the wonderful behaviour of the atoms of carbon. In order to obtain some sort of system whereby the various combinations of carbon can be simply explained chemists picture each carbon atom as being armed with four little links or hooks with which it is able to grapple, as it were, and hold on to other atoms. Each hydrogen atom, likewise, has its hook, but only one instead of four.

Now it is easy to picture to ourselves an atom of carbon in the middle with its hooks pointing out north, south, east and west with a hydrogen atom linked on to each. That gives us a picture of the molecule of Methane, the gas which forms the chief const.i.tuent of coal gas such as we burn in our homes. Methane is also given off by petroleum and it is the cause of the explosions in coal mines, being known to the miners as "firedamp." It is the first of a long series of substances which the chemist called paraffins. The first, as you see, consists of one of carbon and four of hydrogen. Add another of carbon and two more of hydrogen and you get the second "Ethane." Add the same again and you get the third, Propane, and so on until you can reach a substance consisting of thirty-five parts of carbon and seventy-two parts of hydrogen. All we need trouble about, however, is the first two, Methane and Ethane.

We have pictured to ourselves the molecule of methane: let us do the same with ethane. Imagine two carbon atoms side by side linked together or hand in hand. Each will be using one of its hooks to grasp one hook of its brother atom. Hence each will have three hooks to spare on to which we can hook a hydrogen atom. Thus we get two of carbon and six of hydrogen neatly and prettily linked up together. The atoms form an interesting little pattern and to build up the various paraffin molecules with a pencil and paper has all the attractions of a puzzle or game. All you have to do is to add a fresh atom of carbon alongside the others and then attach an atom of hydrogen to each available unused hook. If you care to try this you will get the whole series, each one having one atom of carbon and two of hydrogen more than its predecessor.

If you mix together a quant.i.ty of methane and an equal quant.i.ty of chlorine, which I have shown you in another chapter how to get from common salt, a change takes place, for in each molecule of methane one hydrogen atom becomes detached and an atom of chlorine takes its place.

How or why this change occurs we do not know. It is a fact that the chlorine has this power to oust the hydrogen and there we must leave it, for the present at any rate. The substance so formed is called methyl chloride.

In another chapter reference has been made to that substance which is made from common salt and which is so important in so many manufactures called caustic soda. If we bring some of it into contact with the methyl chloride the chlorine is punished for its rudeness in displacing the hydrogen; it is paid back in its own coin, for it is in turn displaced not this time by a single atom but by a little partnership called "hydroxyl" one atom of hydrogen and one of oxygen acting together. We can again form a neat little picture of what happens. The oxygen atom has two hooks, one of which it gives to its friend the hydrogen atom and thus they go about hand-in-hand, the oxygen having one unused hook with which to hook on to something else. In this case it hooks on to that particular hook from which it pushes the chlorine.

We have thus seen two changes take place. First, the hydrogen is displaced by the chlorine: then the chlorine is turned out and its place taken by the hydroxyl. And during both these changes the central carbon atom and its three hydrogen partners have remained unaffected. Those four atoms are called the methyl group, and a methyl group combined with a hydroxyl group forms _methyl alcohol_.

Similar changes can be brought about with Ethane as with Methane, and in them the two carbon atoms and the five hydrogen remain unchanged, whence they too are regarded as a group, the Ethyl group, and an ethyl group hooked on to a hydroxyl group gives us a molecule of _ethyl alcohol_.

These groups of which we have been speaking never exist separately except at the moment of change, but in the wonderful changes which the chemist is able to bring about the atoms forming these groups seem to have a fondness for keeping together and moving together from one substance into another. In a word, they behave as if they were each a single atom and they are called by the name of Radicles; the word simply means a little root.

The methyl radicle and the ethyl radicle, since they form the basis of two of the paraffin series, are called paraffin radicles, so that we can describe this useful alcohol as a paraffin radicle with a hydroxyl radicle hooked on to it. If we use the methyl radicle we get methyl alcohol: if we use the ethyl radicle we get ethyl alcohol.

Now ethyl alcohol is the spirit which is contained in all strong drink.

Whiskey has as much as 40 per cent and brandy and rum about the same, while ale has only about 6 per cent. All of them may be regarded as impure forms of ethyl alcohol, the various impurities giving to each its particular taste.

Ethyl alcohol, too, is what is sold at chemists' shops as "spirits of wine," where also we can purchase that which is familiar as "methylated spirits," whereby there hangs a tale.

All Governments regard alcohol for drinking as a fit subject for taxation. When anyone buys a drink with alcohol in it a part of what he pays goes to the Government in the form of duty. On the other hand, when alcohol is used for trade purposes, for making varnish or something like that, there is no reason whatever why it should be charged with duty.