February, 1915. 



KNOWLEDGE. 



57 



salt solution. The frequency of the oscillations is not 

 exceedingly high ; and, since the resistance of the tissues 

 is great, the current is not confined to the outer parts of 

 the conducting tissues, as would occur \\-ith better con- 

 ductors and higher frequency. The electrodes and currents 

 can be arranged so as to cause a rise of temperature of a few- 

 degrees only, or the electrical heating may be concentrated 

 on a portion of tissue which it is desired to coagulate and 

 destroy, ^\^len the former method of application is employed 

 the whole body is heated, and the skin becomes bathed in 

 sweat, owing to the convection of the heat by the blood. 

 Some interesting experiments are described, in one of which 

 albumen is coagulated in tlie space between the electrodes 

 connected to the diathermy apparatus, and in another 

 a cube of raw meat is charred. Two disc electrodes, one 

 inch in diameter, are placed on opposite sides of the cube. 

 A central bridge of meat^is soon cooked, and is finally 

 charred. 



RADIO-ACTIVITY. 



By Alexander Fleck, B.Sc. 



MEDICAL USES FOR RADIUM.— Early in the histon.' 

 of radio-acti\'it>' it was disco\ered that the rays produced 

 by atomic disintegration had some effect on the tissue of 

 organisms, and in recent years many in the medical pro- 

 fession have turned their attention to directing such effects 

 to alleviate and cure various diseases. In some forms of 

 disease, such as rodent ulcers, a cure ma^' be confidently 

 expected, provided that sufficient quantities of radium are 

 used. In other and more serious diseases, as, for example, 

 cancer, it is not yet possible to say that a complete cure can 

 be looked for. It seems, however, that the malignancy 

 of the disease is mitigated by the application of radium, and 

 often a cure lasting for a number of years has been obtained. 

 -■Vlthough the disease may recur, it does not necessarily 

 follow that it will do so. The position taken up by the 

 London Radium Institute and most medical men is that, 

 whenever the cancer is at all operable, an excision is made, 

 and the radium treatment reserved for inoperable cases. 

 Considerable hope is entertained that, by judicious com- 

 bination of radium treatment and e.xcision, cancer will 

 soon cease to be the terrible scourge that it is at present. 



London, of course, has had for some years now a large 

 quantity of radium available for medical purposes, and 

 several other cities in the United Kingdom have recently 

 purchased quantities to be set aside for use in the treatment 

 of disease. 



RADIO-ACTIVITY AT THE BRITISH ASSOCIATION. 

 — In the issue of Nature for November 26th a report is 

 given of the proceedings of Section A (Physical) of the 

 meeting in Australia, and it seems that pure radio-activitj^ 

 occupied a minor position, while the allied subject of radi- 

 ations in general was discussed in a number of important 

 aspects. From the point of view of the radio-active chemist, 

 the most interesting was a joint discussion with the 

 Chemistry Section on the structure of atoms and molecules. 

 Professor H. E. Armstrong seems to have been the chief 

 representative of chemistry, and contributions were made 

 by Sir E. Rutherford, Professor Nicholson, l\Ir. IMoseley, 

 and others. Professor Hicks dealt with the subject from 

 the spectroscopic point of view, and stated that neither by 

 the Thomson nor the Rutherford atom is it easy to explain 

 the spectra of the elements. The real atom seems to 

 be something more complicated than either of these models. 

 The meeting is said to have been more of a s>Tnposium 

 than a discussion ; and, while no new facts or principles of 

 importance have been enunciated, the full report which it 

 is promised will be published in the annual British 

 Association volume will be awaited with interest. 



FORMATION OF ACTIVE DEPOSITS.— Very shortly 

 after the discovery of radium emanation it was found that 

 if two metal plates, one positively and the other negatively 

 charged, were placed for a few hours in a space available 



to this gas, the negatively charged plate became intensely 

 active, whilst the positive plate had only a very small 

 acti\-it5-. The material that produces the activities so 

 obtained is called the " active deposit." 



It is easily proved that the emanation itself is not affected 

 by the electric field, and that therefore it is electrically 

 neutral. The emanation in its disintegration gives oft 

 an a-particle, carrj-ing two positive unit charges, and there- 

 fore we should expect that the remaining part of the ema- 

 nation atom (i.e., after taking away positive electricity from 

 a neutral body) would be negatively charged. If this were a 

 complete explanation of the disintegration of the ema- 

 nation, then the active deposit material would be attracted 

 to the positive plate in place of being, as it actually is, 

 collected on the negative plate. This anomaty is explained 

 by the Uberation of a number of low-speed negatively 

 charged 5-rays by the a-particle in its passage through the 

 atom. There remains, however, the question as to how the 

 small quantity of active deposit is obtained on the positive 

 plate, and tliis problem has been attacked in a number of 

 papers which have recently appeared in the Philosophical 

 Magazine (papers by WelUsch, Walmsley, and Lucian). 

 The main conclusion in aU cases is the same, namely, that 

 when the A member of the active deposit (i.e., the first 

 disintegration product after the emanation) is formed, it 

 always carries a positive charge, but that, just as in the case 

 of an ordinar^^ gas ion, in the course of diffusion it may 

 recombine with another negative ion to become electrically 

 neutral. \Mien this happens this neutral particle will be 

 deposited on the first surface that it meets. The small 

 quantity of active deposit material referred to is therefore 

 obtained from those particles rendered neutral by re- 

 combination which have chanced to come into contact with 

 the positively charged surface. 



SEPARATION AND PURIFICATION OF RADIUM. 

 — In a uranium-bearing mineral the greatest possible amount 

 of radium (except in very rare circumstances) that may be 

 present is 3-23 parts of radium for every ten million parts 

 of uranium, and the task of separating this very small 

 amount of material is one that demands a considerable 

 amount of chemical skill. As it is first separated, the radium 

 is contained in a mixture of barium, lead, and other sub- 

 stances, of which the sulphate is comparatively insoluble. 

 The concentration at this stage is usually about 0-2 to 0-5 

 of a milligramme of radium per kilograrmne of material. 

 This sulphate has then to be converted into some soluble 

 salt, usually the chloride, sulphuretted hydrogen, and then 

 ammonia added to the solution so obtained in order to 

 remove elements of the lead and iron groups respectively. 

 Finally, the radium is obtained in the filtiate from these 

 elements along with the barium. At this stage the pro- 

 cedure is transferred from the works to a chemical laboratory, 

 and the long process of fractionation is commenced. This 

 consists in making a hot concentrated solution of the 

 barium-radium chlorides, which is allowed to cool. It is 

 found that the crj'stals that separate out are richer in 

 radium than the material that remains in solution (usually 

 in the ratio of 5 to 1). This process is repeated a great 

 many times until finally pure radium is obtained. The 

 physical chemistry of the process is verj' interesting, because 

 it IS usually taught that by crj'stalUsing a substance from 

 solution a small quantity of impurity will remain in the 

 liquid, and that the crj'stals will be pure. In the above case 

 the exceptionally small quantities of radium present are 

 concentrated in the crystals. It is found by experience 

 that lead also accumulates in the crystals, and it has to 

 be separated frequently by sulphuretted hydrogen or some 

 other means. 



In some Austialian works this process is considerably 

 modified, and an account was given during the course of 

 last year by Radcliff to the Sydney Section of the Society 

 of Chemical Industry', in which pure barium-radium 

 chloride was obtained by saturating the solution obtained 

 from the crude sulphates with hydrochloric-acid gas. 



