Chemical actions.
123. Rays from active radium preparations change oxygen into ozone[[210]]. Its presence can be detected by the smell or by the action on iodide of potassium paper. This effect is due to the α and β rays from the radium, and not to the luminous rays from it. Since energy is required to produce ozone from oxygen, this must be derived from the energy of the radiations.
The Curies found that radium compounds rapidly produced coloration in glass. For moderately active material the colour is violet, for more active material it is yellow. Long continued action blackens the glass, although the glass may have no lead in its composition. This coloration gradually extends through the glass, and is dependent to some extent on the kind of glass used.
Giesel[[211]] found that he could obtain as much coloration in rock-salt and fluor-spar by radium rays, as by exposure to the action of cathode rays in a vacuum tube. The coloration, however, extended much deeper than that produced by the cathode rays. This is to be expected, since the radium rays have a higher velocity, and consequently greater penetrating power, than the cathode rays produced in an ordinary vacuum tube. Goldstein observed that the coloration is far more intense and rapid when the salts are melted or heated to a red heat. Melted potassium sulphate, under the action of a very active preparation of radium, was rapidly coloured a strong greenish blue which gradually changed into a dark green. Salomonsen and Dreyer[[212]] found that plates of quartz were coloured by exposure to radium rays. When examined minutely, plates cut perpendicular to the optic axis showed the presence of lines and striae, parallel to the binary axes. Adjacent portions of the striated system differed considerably in intensity of coloration and clearly revealed the heterogeneity of structures of the crystal.
The cause of these colorations by cathode and radium rays has been the subject of much discussion. Elster and Geitel[[213]] observed that a specimen of potassium sulphate, coloured green by radium rays, showed a strong photo-electric action, i.e. it rapidly lost a negative charge of electricity when exposed to the action of ultra-violet light. All substances coloured by cathode rays show a strong photo-electric action, and, since the metals sodium and potassium themselves show photo-electric action to a very remarkable degree, Elster and Geitel have suggested that the colorations are caused by a solid solution of the metal in the salt.
Although the coloration due to radium rays extends deeper than that due to the cathode rays, when exposed to light the colour fades away at about the same rate in the two cases.
Becquerel[[214]] found that white phosphorus is changed into the red variety by the action of radium rays. This action was shown to be due mainly to the β rays. The secondary radiation set up by the primary rays also produced a marked effect. Radium rays, like ordinary light rays, also caused a precipitate of calomel in the presence of oxalic acid.
Hardy and Miss Wilcock[[215]] found that a solution of iodoform in chloroform turned purple after exposure for 5 minutes to the rays from 5 milligrams of radium bromide. This action is due to the liberation of iodine. By testing the effect of screens of different thicknesses, over the radium, this action was found to be mainly due to the β rays from the radium. Röntgen rays produce a similar coloration.
Hardy[[216]] also observed an action of the radium rays on the coagulation of globulin. Two solutions of globulin from ox serum were used, one made electro-positive by adding acetic acid, and the other electro-negative by adding ammonia. When the globulin was exposed close to the radium in naked drops, the opalescence of the electro-positive solution rapidly diminished, showing that the solution became more complete. The electro-negative solution was rapidly turned to a jelly and became opaque. These actions were found to be due to the α rays of radium alone.
This is further evidence in favour of the view that the α rays consist of projected positively charged bodies of atomic dimensions, for a similar coagulation effect is produced by the metallic ions of liquid electrolytes, and has been shown by W. C. D. Whetham[[217]] to be due to the electric charges carried by the ions.
124. Gases evolved from radium. Curie and Debierne[[218]] observed that radium preparations placed in a vacuum tube continually lowered the vacuum. The gas evolved was always accompanied by the emanation, but no new lines were observed in its spectrum. Giesel[[219]] has observed a similar evolution of gas from solutions of radium bromide. Giesel forwarded some active material to Runge and Bödlander, in order that they might test the gas spectroscopically. From 1 gram of a 5 per cent. radium preparation they obtained 3·5 c.c. of gas in 16 days. This gas was found, however, to be mainly hydrogen, with 12 per cent. of oxygen. In later experiments Ramsay and Soddy[[220]] found that 50 milligrams of radium bromide evolved gases at the rate of about 0·5 c.c. per day. This is a rate of evolution about twice that observed by Runge and Bödlander. On analysing the gases about 28·9 per cent. consisted of oxygen, and the rest hydrogen. The slight excess of hydrogen over that attained in the decomposition of water, they consider to be due to the action of oxygen on the grease of the stop-cocks. The radio-active emanation from radium has a strong oxidizing action and rapidly produces carbon dioxide, if carbonaceous matter is present. The production of gas is probably due to the action of the radiations in decomposing water. The amount of energy required to produce the rate of decomposition observed by Ramsay and Soddy—about 10 c.c. per day for 1 gram of radium bromide—corresponds to about 30 gram-calories per day. This amount of energy is about two per cent. of the total energy emitted in the form of heat.
Ramsay and Soddy (loc. cit.) have also observed the presence of helium in the gases evolved by solution of radium bromide. This important result is considered in detail in [section 267].