October, 1908.] 



KNOWLEDGE. 



219 



charged particles of the dimensions of au ordinary atom, 

 moving with a fairly small velocity ; Prof. Rutherford 

 estimates that their velocity is ahout 25 x 10^ cms. per 

 second. The high i)enetrative capacity of the /3 rays leads 

 to the conclusion that they consist of streams of exces- 

 sively small negatively charged particles moving with a 

 very great velocity ; they are probably identical with those 

 discovered by Prof. J. J. Thomson, each possessing a mass 

 equal to about a one-thousandth part of the mass of a 

 hydrogen atom ; their velocity is probably comparable 

 with that of light. 



In addition to the a and ;3 rays, radium emits a small 

 quantity of very highly penetrative rays, termed the y rays. 

 These can penetrate a cousidenible thickness of aluminium, 

 and are not deflected in a magnetic field ; it is now gene- 

 rally held that they are closely related to, if not identical 

 with, X-rays. 



An important step has lately been achieved by Prof. 

 Rutherford and Mr. Soddy. These experimenters caused 

 air to bubble slowly through water in which a small trace 

 of a thorium salt was dissolved, after which it was led 

 through a lead tube into the case of a charged electroscope. 

 The charge of the electroscope was seen to rapidly diminish, 

 showing that the air carried charged particles away from 

 the radio-active solution Part of the lead tube through 

 which the air passed was coiled into a spiral, and this was 

 next placed in a jacketing vessel containing liquid air. On 

 re-charging the electroscope, it was found that the charge 

 scarcely diminished. Prom this it was concluded that the 

 charged particles which had previously been carried into 

 the electroscope had become condensed in passing through 

 the cooling spiral. 



Struck by the results just described. Sir William 

 Ramsay conceived the brilliant idea that the substance 

 condensed in the cooling worm was a gas. To tt^st this 

 point, a small quantity of radium was placed in an ex- 

 hausted vessel communicating with a bulb immersed in 

 liquid hj'drogen. After some months the substance con- 

 densed in the bulb was pumped into a vacuum tube, when 

 a spectroscopic examination showed that this substance 

 was helium ! Prom this the conclusion is drawn, that the 

 a rays consist of streams of charged helium atoms. 



Where has this helium come from ? There is no reason 

 to suppose that helium was present, as helium, in the 

 radium salt ; our only alternative is to suppose that the 

 element radium possesses the unique property of spon- 

 taneously decomposing into other elements, one of which 

 is helium ! In this connection it should be noted that the 

 high atomic weight of radium indicates that the atoms are 

 of a complicated structure ; jserhaps it may be found iilti- 

 malcly that tlio elements of high atomic weight, at one end 

 of the Mendelaef series, are capable of spontaneous trans- 

 mutation into the elements at the other end of the series 



Is, then, the dream of the alchemists about to be 

 realized ? It would appear so, at any rate in part ; but in 

 place of other substances being transmutable into gold, it 

 would appear more probable that gold (an element of 

 fairly high atomic weight) may be capable of transmutation 

 into helium or other gases. 



When radium is placed in the dark, it phosphoresces 

 spontaneously for an iudetinitely long period. Sir William 

 and Lady Huggins have examined the spectrum of the 

 light thus emitted, and find that after several days' 

 exposure, a photograph plat* shows a number of definite 

 lines, some of which correspond to lines in the spectrum 

 of helium. This result confirms the conclusions arrived at 

 by Sir William Ramsay. 



Before the above results had been obtained, Prof. 

 Curie had found that a fragment of radium, when placed 

 in an isothermal enclosure, maintains itself constantly at 



a temperature about TS'^ C. above its surroundings. A 

 gram of radium, in one hour, emits alx)ut 100 gram-calories 

 of heat, and could, therefore, continue indefinitely to melt 

 more than its own weight of ice per hour. 



To what extent can we now form a scheme of explanation 

 of this phenomenon ? At present the highest authorities 

 would mostly subscribe to the following theory. The 

 compUcated radium atom is continually breaking down 

 into the atoms of simple elements, of which one is helium. 

 In this process a large amount of energy is liberated by 

 the decomposition of each radium atom ; thus the helium 

 atoms are flung off vfith a great velocity, and, therefore, 

 possess much kinetic energy, and in the interior of the 

 radium this energy is transformed, during collisions, into 

 heat. At the outside of the radium the helium atoms 

 escape, carrying positive charges, and constitute the a, rays. 

 Sir William Crookes has invented au instrument, termed 

 the spinthariscope, by the aid of which this escape can be 

 observed. A particle of radium is placed in front of a 

 fluorescent screen, and the latter is examined by means of 

 a lens ; smalt luminous points continually flash out on the 

 screen and gradually die away, indicating the points struck 

 by the escaping particles. 



Minute negatively charged particles or electrons are 

 also thrown off during tiie above process, and these 

 constitute the ^ rays. The latter particles striking on the 

 radium itself, or surrounding objects, give rise to feeble 

 X-rays, just as the cathode stream in a vacuum tube 

 excites X-rays in objects on which it falls ; this accounts 

 for the y rays. The greatest outstanding mystery is 

 encountered when we try to explain why the radium atom 

 decomposes. If decompositions are due to collisions, it 

 might be supposed that a cousidei-able moleculous velocity, 

 which is eqiiivalent to a fairly high temperature, would be 

 necessary ; but Prof. Dewar has found that radium, even 

 when surrounded by liquid hydrogen, still emits radiations 

 which can discharge an electroscope, and which presumably 

 constitute ^ and y rays. The rate at which decomposition 

 progresses is extremely slow. Prof. Rutherford estimates 

 that in a year a gram of radium emits about 021 c.c. of 

 helium, and this would correspond to a loss of weight of 

 less than a tenth of a milligram. No conclusive evidence 

 of any loss of weight has so far been observetl. 



In conclusion, attention may be drawn tt) the physio- 

 logical effects of radium emanations. If a suiall fragment 

 of radium, sealed up in a glass tube, is carried for a few 

 hours in a waistcoat pocket, the skin nearest to the radium 

 is afterwards found to be blistered. It appears that radium 

 emanations destroy all living tissue; they have also been 

 found to be bactericidal. Prof. Curie states, that he would 

 be afraid to enter a room containing a j>ound of radium ; 

 he anticipates that, if he did so, his skin would be blis- 

 tered, his eyesight destroyed, and probably deatii would 

 ultimately occur. Feeble radium emanations may. how- 

 ever, in the near future be found to possess valuable 

 therapeutic properties. Thus Prof. Kutherforil suggests 

 that the inhalation of air which has bubbleil throngii a 

 dilute solution of thorium, might prove valuable in the 

 treatment of consumption. X-r.iys have been found to 

 cure superficial cancers; they probably do this by destroying 

 the cancerous tissue. In the treatment of cleep-seated 

 cancer. X-rays cannot be used; they are necessarily applied 

 from the outside, and would have to destroy the healthy 

 external tissues liefore they could reach the cancer. It 

 has, however, been suggested that a small scaled tube 

 containing i-idiuin might be introduced into the midst of 

 an internal cancer, and thus destroy the latter without 

 affecting the healthy tissues Prof. J. J. Thomson has 

 found that many well-waters are radio-active, and since 

 the Bath waters have been found, by Sir William Ramsay. 



