1912] on Vital Effects of Badii/m and other Bays. 807 



oate that it must always remain exceedingly scarce and of a forbidding 

 price. Naturally, therefore, those interested in its therapeutical 

 properties are anxious to know whether among other radio-active 

 substances there may be any which can take its place, and perhaps 

 be more easily available to the profession, and, through them, to the 

 public. Uranium, thorium and actinium are radio-active, and have 

 all been suggested in this connexion, but they are too feeble to have 

 real efficacy. The discovery by Otto Hahn of a substance known as 

 meso-thorium, which is one of the disintegration products of thorium, 

 and was found in the course of an attempt to separate radio-tlidrium 

 directly from thorium, has aroused considerable expectation. 



Meso-thorium is obtainable from the residues in the preparation 

 of thorium for the manufacture of incandescent gas mantles. It 

 emits the same rays as radium, and, weight for weight, is more power- 

 ful. As the supply of thorium is much larger than that of pitchblende, 

 from which thorium is obtained, we may hope to have a larger 

 supply of meso-thorium. It will cost much less, but, on the other 

 hand, it has a short life of only about seven years, as against radium 

 which lasts 2500 years. It is being experimented with medicalk in 

 Germany. I applied the tube now shown, which is equivalent to 

 10 milligrams of pure radium, to a chronic patch of ic-ray dermatitis 

 on my hand, and a reaction followed 15 days after application, and 

 the result promises to be favourable. 



[Show meso-thorium.] 



Thorium Emanation from Radio-Thorium. — Radio-thorium gives 

 off thorium emanation richly. This is a heavy gas, lasting 76 seconds, 

 giving off alpha rays in profusion. These rays, impinging upon a 

 sulphide of zinc screen, cause it to glow or fluoresce. Sulphide of 

 zinc crystals sparkle and emit light when mechanically crushed or 

 disturbed, and therefore the alpha rays, striking these crystals, cause 

 them to give out light. A remarkable spinthariscope effect is ob- 

 served when the screen is viewed with a magnifying glass. 



The emanation of radium will act like that of thorium, but, 

 instead of lasting only seventy-six seconds, it will lose half its strength 

 in about four days. Thorium emanation also resembles that of 

 radium in giving rise to an " active deposit." This becomes concen- 

 trated on the negative pole in an electric field. A metallic surface 

 can in this way be made intensely radio-active, giving forth the alpha, 

 beta and gamma rays. The "active deposit" from thorium emana- 

 tion lasts for several hours. 



[Show thorium emanation from radio-thorium and 

 screening effects. Blow emanation into sulphide of 

 zinc screen and also blow through long tubes.] 

 Vol. XX, (No. 106) y 



