August i 



1903] 



NATURE 



355 



ince to the bodv^ 



owing o e^g oxvgen was withdrawn bv ignited phcs- 

 hairs ot tne?^^ visible residue was left. When, however, 

 , °'^f°J^fc,'as was introduced, so as to come into contact 

 11. i the top of the tube, and then withdrawn, the eman- 

 ation was found to be present in it in unaltered amount, 

 it appears, therefore, that phosphorus burning in oxygen 

 ind sparking with oxygen have no effect upon the gas so 

 Ml- as can be detected by its radio-active properties. 



The experiments with magnesium-lime were more strictly 

 quantitative. The method of testing the gas before and 

 after treatment with the reagent was to take i /2000th part 

 of the whole mixed with air, and after introducing it into 

 the reservoir of an electroscope to measure the rate of dis- 

 charge. The magnesium-liine tube glowed brightly when 

 the mixture of emanation and air was admitted, and it was 

 maintained at a red-heat for three hours. The gas was 

 then washed out with a little hydrogen, diluted with air 

 ;ind tested as before. It was found that the discharging 

 power of the gas had been quite unaltered by this treat- 

 ment. 



The emanation can be dealt with as a gas; it can be 

 extracted by aid of a Topler pump ; it can be condensed in 

 a U-tube surrounded by liquid air ; and when condensed it 

 can be " washed " with another gas which can be pumped 

 off completely, and which then possesses no luminosity and 

 piactically no discharging power. The passage of the 

 emanation from place to place through glass tubes can be 

 followed by the eye in a darkened room. On opening a 

 stopcock between a tube containing the emanation and the 

 pump, the slow flow through the capillary tube can be 

 noticed ; the rapid passage along the wider tubes ; the 

 delay caused by the plug of phosphorus pentoxide, and the 

 sudden diffusion into the reservoir of the pump. When 

 compressed, the luminosity increased, and when the small 

 bubble was expelled through the capillary it was exceed- 

 ^ ingly luminous. The peculiarities of the excited activity 



^ left behind on the glass by the emanation could also be 



well observed. When the emanation had been left a short 

 time in contact with the glass, the excited activity lasts 

 only for a short time ; but after the emanation has been 

 stored a long time the excited activity decays more slowly. 



The emanation causes chemical change in a similar 

 manner to the salts of radium themselves. The emanation 

 pumped off from 50 milligrams of radium bromide after 

 dissolving in water, when stored with oxygen in a small 

 glass tube over mercury turns the glass distinctly violet in 

 a single night ; if moist the mercury becomes covered with 

 a film of the red oxide, but if dry it appears to remain un- 

 attacked. A mixture of the emanation with oxygen pro- 

 duces carbon dioxide when passed through a lubricated 

 stopcock. 



(3) Occurrence of Helium in the Gases Evolved from 

 Radium Bromide. 

 The gas evolved from 20 milligrams of pure radium 

 bromide (which we are informed had been prepared three 

 months) by its solution in water and which consisted mainlv 

 of hydrogen and oxygen (cf. Gicsel, Ber., 1003, 347) was 

 tested for helium, the hydrogen and o.xygen being removed 

 by_ contact with a red-hot spiral of copper wire, partially 

 oxidised, and the resulting water vapour bv a tube of phos- 



Iphorus pentoxide. 1 he gas issued into a small vacuum- 

 tube which showed the spectrum of carbon dioxide. The 

 vacuum tube was in train with a small U-tube, and the 

 latter was then cooled with liquid air. This much reduced 

 the brilliancy of the CO., spectrum, and the D, line of 

 helium appeared. The coincidence was confirmed by throw- 

 ing the spectrum of helium into the spectroscope through 

 the comparison prism, and shown to be at least within 05 

 of an Angstrom unit. 



The experiment was carefully repeated in apparatus con- 

 -.tructed of previously unused glass with 30 milligrams of 

 radium bromide, probably four or five months old, kindly 



Ilent us by Prof. Rutherford. The gases evolved were 

 passed through a cooled U-tube on their way to the vacuum- 

 tube, which completely prevented the passage of carbon 

 dioxide and the emanation. The spectrum of helium was 

 obtained and practically all the lines were seen, including 

 those at 6677, 5876, 5016, 4^32, 4713, and 4472. There 

 were also present three lines of approximate wave-lengths, 

 bi8o, 5695, 5455, that have not yet been identified. 



NO. 1763, VOL. 68] 



On two subsequent occasions the gases evolved from both 

 solutions of radium bromide were mixed, after four days' 

 accumulation which amounted to about 25 c.c. in each 

 case, and were examined in a similar way. The D, line 

 of helium could not be detected. It may be well to state 

 the composition found for the gases continuously generated 

 by a solution of radium, for it seemed likely that the large 

 e.xcess of hydrogen over the composition required to form 

 water, shown in the analysis given by Bodljinder (Ber., loc. 

 cit.) might be due to the greater solubility of the oxygen. 

 In our analyses the gases were extracted with the pump, 

 and the first gave 286, the second 292 per cent, of oxygen. 

 The slight excess of hydrogen is doubtless due to the 

 action of the o.xygen on the grease of the stopcocks, which 

 has been already mentioned. The rate of production of 

 these gases is about 05 c.c. per day for 50 milligrams of 

 radium bromide, which is more than twice as great as that 

 found by Bodlander. 



(4) Production of Helium by the Radium Emanation. 



The maximum amount of the emanation obtained from 

 50 milligrams of radium bromide was conveyed by means 

 of oxygen into a U-tube cooled in liquid air, and the latter 

 was then extracted by the pump. It was then washed out 

 with a little fresh oxygen, which was again pumped off. 

 The vacuum tube sealed on to the U-tube, after removing 

 the liquid air, showed no trace of helium. The spectrum 

 was apparently a new one, probably that of the emanation, 

 bui- this has not yet been completely examined, and we 

 hope to publish further details shortly. After standing 

 from July 17 to 21, the helium spectrum appeared, and the 

 characteristic lines were observed identical in position with 

 those of a helium tube thrown into the field of vision at 

 the same time. On July 22 the yellow, the green, the 

 two blues and the violet were seen, and in addition the 

 three new lines also present in the helium obtained from 

 radium. A confirmatory experiment gave identical results. 



We wish to express our indebtedness to the research 

 fund of the Chemical Society for a part of the radium usefl 

 in this investigation. 



OJV THE INTENSELY PENETRATING RAYS 



OF RADIUM.^ 

 "D ADIUM is known to emit three types of radiation. 

 These are : — 

 (i) The o rays, very easily absorbed by solids, and carry- 

 ing a positive electric charge. 



(2) The j3 rays, more penetrating than these, and nega- 

 tively charged. 



(3) The 7 rays, intensely penetrating, and not conveying 

 an electric charge at all. 



In a paper published in the Vhil. Trans, for 1901, I 

 investigated the relative ionisations of gases by the a and 



rays. The present communication may be regarded as 

 a sequel to that one, and deals with the 7 rays. 



The radium employed was of activity 1000 (uranium =1), 

 and was contained in a glass cell, over which was cemented 

 a piece of thin aluminium. The cell was placed in a cavity 

 in a block of lead, and over it was placed a disc of lead 



1 cm. in thickness. This it was considered would suffice 

 to suppress all but the 7 rays, which are much the most 

 penetrating. 



In measuring the electrical leakage, the electroscope 

 method was employed. The apparatus was that described 

 in a paper published in the Philosophical Magazine for 

 June, p. (i8i. 



The radium, covered by the thick lead, was placed under 

 the apparatus, and the rate of leak determined when the 

 different gases filled the testing vessel. 



The conditions were, of course, arranged so as to use a 

 saturating P^M.F. The 7 rays are so penetrating that 

 there can be no question of their being appreciably absorbed 

 in a moderate thickness of gas. 



For the methods of preparation of the gases I must refer 

 to the former paper {Phil. Trans., A., vol. excvi., 1901, 

 p. 508). , 



1 By Hon. R. J. Strutt, Fellow of Trinily College, Cambridge. Com- 

 municated to the Royal Society by Lord Rayleigh, F.R.S. Received 

 August 5. 



