WHAT WE KNOW OF RADIUM.

Star (Christchurch), Issue 7923, 30 January 1904, Page 4

WHAT WE KNOW OF RADIUM.

THE CHANGING OE THE ELEMENTS. (By SIR WILLIAM RAMSAY,* in the "Daily Mail.") The story of the discovery of radium is full of interest, and my readers may pardon me even if it is again told ; for it forme the first chapter in a volume of which' many have still to be written. M. Henri Becquerel, prompted by a hint from the celebrated mathematician M. Poincare, discovered that the compounds of uranium, a somewhat rare metal, as well as the metal itself, were capable of impressing a photographic plate wrapped up in black paper, or otherwise protected from light. It was also found that such salts, placed near a charged electroscope, discharged it, the gold leaves falling together. An electroscope, it may be explained, is a metal box with glass sides ; through a hole in the lid a wire passes, the stopper which closes the hole and supports the wire being made of sulphur, or sealing-wax, or some other material which does nd. conduct electricity, j From the end of the wire are suspended, two pieces of gold leaf, hanging down so as to be visible through the glass sides of the box. THE GOLD LEAVES IN THE BOX. If a piece of sealing-wax is rubbed, so as to excite it electrically, and 1 if the projecting end of the wire is touched with the rubbed sealing-wax, a small charge of electricity is given to the wire, and through it to the gold leaves, so that they repel each other, and fly apart, making a figure like an inverted V (A). If the wire be touched with the finger the electric charge is conducted- away through the body, and the leaves swing back into their original posi- , tion. This effect of discharging was found tobe produced when a salt or 1 mineral containing uranium was placed inside the box. •Mdme Curie, a Polish lady, living in Paris, noticed that the rate at which the gold leaves fell together was more rapid with certain uranium) minerals (specimens of pitch-blende) than could be accounted for by the uranium oxide in the mineral ; she therefore separated the mineral into its groups of constituents — uranium, iron, lead, barium, bismuth, etc. (for the mineral contains all these and many other elements), • and tested each group as to its power of flischarge. At first she thought that she had traced the discharging power to the bismuth group, and attributed it to an element which she named "polonium," after ber native country. ■ OTHER ELEMENTS. This discovery has not been disproved; but ib appears that the amount of polonium obtainable is exceedingly small, and difficulb to separate fron. bismuth. Subsequently Mdme Curie discovered another element of the barium group, possessing enormous powers of discharge, and to this element, which occurs in relatively greater amount, she gave the name "radium." It is an undoubted element in the sense in which that term is generally used; its salts resemble closely those of barium', and its spectrum has been observed by M. Demarcay, by Professor Runge, and by Sir William Crookes. Its atomic weight has been determined by Mdme Curie as 225 ; the atomic weight of uranium is the highest known — 240; and there is some evidence from its spectrum, that radium may have even a higher atomic weight — over 250 — and that the sample analysed by Mdme Curie may not have been quit 6 free from barium, of which the atomic weight is only 137. While these researches were in progress M.- Curie and Dr Schmidt discovered simultaneously that another element, thorium, of which the atomic weight is 232, also possesses tbe power of discharging an electroscope; and, moreover, that if air be led over salts of thorium, the air acquires and retains for a short time discharging power. FURTHER DISCOVERIES., The subject was taken up by Professor Rutherford, of Montreal, and by Mr Frederic Soddy, who then worked inh's laboratory ; amd they found that if t_e " active " air were cooled by passing it through a tube cooled with liquid air, ifc lost its "activity," the active portion remaining in the cold tube. On warming the tube, the active portion was carried forward, and with ib the discharging power. They also found that a similar "emanation," or gas, was evolved from salts of radium, possessing a much more permanent discharging power. While the "emanation " from thorium salts "decayed" in a few minutes, that from radium salts lasted a month. It, too, was condensable when cooled; it was , luminous, and imparted temporary lumi- ■ nosity to objects which it touched (" excited activity"). The fact that a radium salt is always hotter than its surroundings, discovered by the Curies_ implies that radium is continually losing energy; and' 1 if the radium, salt be dissolved in water some of this energy is expended in decomposing ai portion of the water into oxygen and hydrogen gases. Professor Rutherford and H. T. Barnes have recently shown that " more than twothirds of the beating effect is not due to the radium at all, but to the radio-active emanation which it produces from itself." In November, 1902, Messrs Rutherford and Soddy concluded) from their experiments on the emanations from 1 radium amd thorium that they are "inert gases, analogous in nature to the members ■■ of the argon family," and also threw out tbe surmise, " whether the presence of helium in minerals and its invariable association with uranium amd thorium may not be connected witb the radio-activity." THE NATURE OF ELEMENTS. Now, I had the good fortune to discover beliun. in 1895 ; it is one of . the argon gases, and is contained in certain minerals ; and when. Mr Soddy caime to work with me in the early summer of this year, we tested the truth of tbis surmise, and we were rewarded! witb success. The fresh emanation from radium does not show : the spectrum) of 'helium ; but as it "decays," heKum. is produced in minute but ever-increasing' quantity. , We can help ourselves by an analogy. Very complicated compounds of carbon and hydrogen ca<n be produced ; one containing thirty atoms of carbon and sixty- two atoms of hydrogen is known. But one of, say, . 200 atoms of carbon and 402 of hydrogen _ would almost certainly fall to nits; it •would split. up and give out beat. The supposition appears reasonably tbat just as there is a limit to the possible number of atoms in such compounds (for the molecules or groups of atoms fall apart hy their own; weight), so there may be a limit to tbe atomic weight of an element. Those elements with high atomic weight, such as ..thorium, uranium and radium, are, apparently decomposing into elements "with low atomic weight; in doing! so they give off heat, and also possess th© curious property of radio-activity. What these elements are is unknown, except in one case ; one of the products of the decomposition of the emanation from radium is helium. Can the process be reversed? No one knows. But as gold is an element of high atomic weight, it may. be confidently stated that if it is changing it is much more likely that it' is being converted into silver and capper tban that it is being formed from them. At this stage, however, lation is futile. It is certain that further experiments will lead to more positive knowledge of the nature of the elements, and of the transformations whioh at least, some of them are und^going.