300Figure IV
Figure IV
Figure IV
When a vacuum is produced in the receiver,, which contains air charged with the emanation, and when the radiation of the receiver is measured immediately after the extraction of the air, it is found that the radiation has not changed at the moment when the active air is withdrawn. The Becquerel radiation of air charged with the emanation does not, then, produce any action in this experiment. This radiation probably exists, but it is composed of very slightly penetrating rays, incapable of passing through the glass wall. In this connection the following experiment can be performed. One of the ends of the metallic tube,(Fig. IV.), communicates atby means of a rubber tube with a receiver,, in which is a solution of a radium salt. The other end of the tube,, is closed with an insulating stopper,. Through the stopper passes a metallic rod,, connected with an electrometer. The tube,, and the rod,, form a cylindrical condenser. The tube,, is brought to a potential of 500 volts. The metallic tube,, connected with the earth, serves as a guard-tube. When the tube,, is sufficiently active it is removed from the radium, and the intensity of the current passing through the condenser is measured. Then the active air which fills the condenser is rapidly driven out, inactive air is admitted, and a new measurement of the intensity of the current is made immediately. It is found that the current has become six times more feeble. Thus, during the second measurement the radiation of the excited walls acts solely to ionize the air in the condenser, while during the first measurement the emanation acts as well. We may, then, suppose that it also emits an emanation. This radiation is necessarily very slightly penetrating, for its action cannot be detected on the exterior.
When a solid plate which has been excited by the emanation becomes inactive in free air, the law of loss of activity depends on the time during which the plate has been left in contact with the emanation. If the action of the emanation is prolonged (more than twenty-four hours, for example), the law of loss of activity is given by the difference between two exponentials. The intensity of the radiation,, may in this case be represented as a function of the time,, by the equation
0is the intensity of the radiation at the beginning of the time, that is at the moment when the plate is removed from the influence of the emanation.,, andare three constant coefficients:= 4.2;= 0.000413;= 0.000538, taking one second as the unit of time.
These results are represented by the curve 1 (Fig. V.). The logarithm ofis represented on axis of the ordinates, and the time on the axis of abscissas. One hour and a half after the beginning of the loss of activity the second exponential has become negligible with respect to the first in the expression for the value of, and the representative curve has become straight. From this moment the activity diminishes by one-half during each period of twenty-eight minutes.
300Figure V
Figure V
Figure V
If the duration of the action of the emanation is not so long, the law of the variation of the radiation during its loss is much more complex. In Fig. V. are represented the results of experiments for different times of action, as indicated on the corresponding curves. We see, for example, that for a time of excitation of five minutes, the intensity of the radiation during the loss of activity first falls rapidly to a minimum; then it increases, and again begins to fall. Finally, the law of loss of activity tends towards a simple exponential law which is the same as the limiting law after prolonged excitation. These complex phenomena can be explained by assuming that on the excited plate the radioactive energy is in three distinct states, but the demonstrations relative to this subject are too long to have a place in this article.
The emanation from radium causes the energetic phosphorescence of a large number of substances. Glass reservoirs containing air charged with the emanation are luminous, Thuringian glass being the most sensitive. Phosphorescent sulphide of zinc is particularly sensitive to the action of the emanation from radium, and then gives an intense light.
If in a closed space substances become more active the greater the amount of free gas around them. When plates placed parallel to one another, and a short distance apart, are put into a closed space with radium, the faces of each plate become excited in proportion to its distance from the others. When glass tubes of different diameters are filled with the emanation and communicate with one another, the walls of those of greatest interior diameter become most active. These tubes are also most luminous. To interpret these facts it must be assumed that the air charged with the emanation acts on the walls by a radiation that arises in every part of the gaseous mass, and that the radioactivity induced upon a wall is proportional to the flow of exciting radiation received by that wall.
The Slow Evolution of Induced Activity.—A solid body acquires a very feeble, persistent, induced activity when it remains a month or less in contact with the radiation from radium. A substance withdrawn from the influence of the emanation after having been subjected to it for a long time loses its activity rapidly at first, according to the laws given. But the activity of the radiation does not disappear completely. There remains a radiation several thousand times more feeble than it was at first. This radiation is given off with extreme slowness and continues for several years. (The radiation passes through a minimum, then slowly increases for several months, but always remains very slight.)
Occlusion of the Emanation of Radium by Solids.—All solids when excited by contact with the emanation from radium acquire the property of themselves emitting the emanation in very small quantity. They preserve this power for only twenty, minutes from the time they are removed from the space containing the emanation. Nevertheless certain substances as caoutchouc, paraffin, and celluloid have the property of being saturated with the emanation, and of emitting it afterwards in abundance for several hours, or even days.
Induced Activity of Liquids.—When a liquid is placed in a closed space with radium it becomes radioactive. Water, salt solutions, petroleum, etc., can thus be excited. The liquids dissolve a certain amount of the emanation. When an excited liquid is separated from the radium and sealed up in a tube it slowly loses its activity according to the law of the destruction of the emanation (decrease to one-half in four days). When the liquid is placed in a flask open to the air it loses its activity very rapidly, and the emanation spreads into the surrounding air.
Variations of the Activity of Solutions of Radium Salts and of the Solid Salts of Radium.—When a solution of a salt of radium is exposed to the air of a room in an open vessel it becomes almost inactive. The solution emits an emanation that spreads into the room and causes induced radioactivity of the walls. The radiation of the radium is thus externalized. If the solution be enclosed in a sealed tube its activity increases little by little, and tends toward a limiting value that is reached only after several months. No doubt the emanation produced by the radium accumulates in the tube until the velocity of its spontaneous destruction is equalized by the supply from the radium.
We have seen that a salt of radium that has been freshly prepared possesses an activity which increases with the time, and becomes about five times as great as the initial activity. It seems that the emanation emitted by the radium can escape only with difficulty from the solid salt, and that it accumulates there and is transformed at once into induced radiation. An equilibrium is established when the spontaneous loss becomes sufficient to compensate the production.
When solid salt of radium is heated to redness, all the emanation which it had accumulated escapes. When the salt returns to the temperature of the room it emits Becquerel rays to a much less extent. However, the radiation recovers little by little its original value, which is reached after one or two months. The salt which had been heated to redness no longer possesses the power of emitting the emanation, but this property may be restored to it by dissolving it and drying it at a slightly elevated temperature.
Diffusion of the Emanation from Radium.—Danne and I have studied the law of the diffusion of the emanation of radium. A large glass reservoir filled with excited air communicates with the atmosphere by means of a capillary tube. The Becquerel radiation emitted by the walls of the reservoir is measured as a function of the time, and from this is deduced the law of the escape of the emanation through the capillary tube. It is found that the rapidity of the escape of the emanation is proportional to the quantity of it in the reservoir. It varies proportionally to the cross section of the capillary tube, and inversely as its length. These laws are the same as for a gas mixed with air under the same conditions. The coefficient of the diffusion of the emanation into air is equal to 0.100 at 10°. The coefficient is, therefore, of the same order of magnitude as that of the diffusion of carbon dioxide into the air, which is equal to 0.15 at the same temperature.
Radioactivity Induced by Thorium and the Emanation of Thorium.—Thorium emits an emanation and gives rise to the phenomena of induced radioactivity. These properties have been made the subject of numerous researches by Rutherford. The action of thorium is, otherwise, considerably less intense than that of radium.
The emanation of thorium disappears spontaneously according to a simple exponential law, but its disappearance is much more rapid than that of the emanation of radium. The quantity of the emanation from thorium diminishes by one-half in about one minute and ten seconds, while in the case of radium the quantity falls to one half in four days. This considerable difference causes a profound difference in the aspect of the phenomena.
In a closed space of not too great dimensions the emanation from radium spreads almost uniformly into all parts. But under the same conditions the emanation of thorium is found to accumulate in the vicinity of the thorium, because it disappears spontaneously before it has time to diffuse any considerable distance into the air.
The radiant activity of a substance can be measured by placing it upon the lower plate of a condenser formed of two horizontal plates, and measuring the conductivity communicated to the air between the plates. If this measurement be made with oxide of thorium, it is found that the conductivity of the air is greatly decreased when a current of air is sent between the plates. The oxide of thorium emits, indeed, an emanation that accumulates upon the substance and by its radiation helps to ionize the air between the plates. A current of air carries away the emanation as rapidly as it is set free, and the only thing left to cause ionization is the Becquerel radiation coming directly from the thorium.
If the same experiment be repeated with a salt of radium it is found that the current of air produces only a feeble effect. With uranium and polonium, which do not emit the emanation, the current of air has no effect. On the contrary, in the case of actinium, the action of the current of air is to suppress four-fifths of the conductivity of the air. It may be concluded that for thorium, and especially for actinium, the radiation of the emanation is very important in comparison with the radiation of the radioactive substance itself.
When one wishes to excite a solid to saturation with the emanation from thorium, it is necessary to cause the emanation to act for a long time, and hence new supplies of it must be brought continually to the surface of the body that is to be excited. To do this a current of air is passed through a solution of a salt of thorium and, then this current, of air charged with the emanation, is passed over the body. The solid, when excited by the emanation from thorium, loses its activity spontaneously according to an exponential law. The radiation falls to one-half every eleven hours. Hence, contrary to what takes place with the emanations, the activity induced by thorium upon solid substances disappears more slowly than that induced by radium.
Radioactivity Induced by Actinium and the Emanation from Actinium.—Actinium emits an emanation which gives a very intense radiation. This emanation disappears spontaneously with extreme rapidity, and diminishes by one-half in about one second. In air at the atmospheric pressure the emanation emitted by actinium cannot propagate itself to a greater distance than 7 or 8 mm. from the active substance, and excites bodies only when they are placed very near the source. On the contrary, in a vacuum the diffusion is rapid, and a body placed 10 cm. away from the actinium can be excited. The radioactivity induced by the actinium upon solids disappears according to an exponential law. It diminishes to one-half in about thirty-six minutes.
The Concentration of Induced Radioactivity upon Bodies Charged Negatively.—Rutherford showed that a body exposed to the emanation from thorium became much more active when it was charged negatively than when it was at the same potential as the surrounding objects. On the contrary, it became less excited when it had a positive potential. The same phenomenon is noticed in the case of the excitation by radium and actinium. The nature of this curious phenomenon seems to me not to be well established.
Condensation of the Emanations from Radium and Thorium.—Rutherford and Soddy discovered that the emanations from radium and thorium can be condensed at the temperature of liquid air. A current of air charged with the emanation loses its radioactive properties when passing through a coil of tube plunged in liquid air. The emanations remain condensed in the tube, and can be restored to the gaseous state when it is warmed. The emanation from radium condenses at -150°, while that from thorium condenses between -100° and -150°. The experiment can be performed as follows: Two glass reservoirs, one large and the other small, communicate with one another. They are filled with gas excited by radium. The small reservoir is plunged in liquid air. The large reservoir then rapidly becomes inactive, while all the activity is concentrated in the small reservoir. If the two are then disconnected, and the small one be taken from the liquid air, it is seen that the large reservoir is not at all luminous, while the small one gives off more light than at the beginning of the experiment. The experiment is a very brilliant one if the walls of the reservoirs are coated inside with phosphorescent sulphide of zinc.
When a platinum wire excited by thorium or radium is heated to redness, it loses most of its activity. Fanny Cook Gates showed that this radioactivity is transferred to cold solids placed in the vicinity of the wire. It distils in some way, at a sufficiently high temperature, passing through the intermediate form of a gaseous emanation. The induced radioactivity of solids would thus be analogous to a condensed emanation.
Activity Induced by Remaining in Solution in a Radioactive Liquid. Uranium X. Thorium X.—Certain substances are temporarily excited when they stay in the same solution with radioactive substances. Giesel and Mme. Curie prepared active bismuth by dissolving one of its salts in the solution of a salt of radium. Debierne also excited a salt of barium in a solution of a salt of actinium. The barium salt thus excited presents certain analogies to the salt of radium, and can be fractionated in the same way. By crystallization the active chloride is concentrated in the salt that is deposited.
By various methods of chemical precipitation the activity of uranium has been divided (Crookes, Soddy, Rutherford and Grier, Debierne, Becquerel). For instance, barium chloride is added to a solution of uranyl nitrate, and the barium is then precipitated by adding a little sulphuric acid. The precipitated barium sulphate, when separated and dried, is radioactive. It has carried with it a part of the activity of the uranium, for the uranium salt, when the solution is evaporated to dryness, is less active than before it was submitted to this operation. But after several months the sulphate of barium loses its radioactivity, while the uranium salt has regained its original properties. It is evident that the barium was excited by contact with the uranium, or that it occluded in some special form a part of the activity of the uranium (uranium X of Crookes).
Rutherford and Soddy showed that if nitrate of thorium is precipitated by ammonia, the precipitated oxide of thorium is less active than ordinary thorium. The liquid from which it was precipitated is radioactive, and on evaporating it to dryness the small residue is 2,500 times more active than the thoria (they call the radioactive substance in this residue thorium X). After several weeks the residue has lost its activity, the thorium X has disappeared, and the thoria which was precipitated has, on the contrary, regained its normal activity. Further, while the thorium X existed it emitted the thorium emanation in abundance.
Rutherford and Soddy think that uranium X and thorium X are simply intermediate products of the breaking down of uranium and thorium. Thorium, for example, produces thorium X continuously, which breaks down into the emanation of thorium, that is in its turn transformed into induced activity.
Conductivity of Atmospheric Air. Emanation and Induced Radioactivity at the Surface of the Earth—Elster and Geitel, and also Wilson, showed that atmospheric air conducts electricity to a slight extent, that it is always slightly ionized. This ionization seems to be due to various causes. According to the work of Elster and Geitel, atmospheric air always contains a small proportion of an emanation analogous to that emitted by radioactive substances. Metallic wires suspended in the air and kept at a high negative potential become active under the influence of this emanation. At the summits of high mountains the atmosphere contains more of the emanation than on plains or at the level of the sea. The air of caves and caverns is especially highly charged with the emanation. Air rich in the emanation can also be obtained by aspirating, by means of a tube sunk in the earth the air which is contained in it. The air extracted from certain mineral waters contains the emanation, while the air dissolved in the water of the sea and of the rivers is almost free from it.
The conductivity of the atmosphere is also probably due in part to very penetrating radiations that traverse space, and of which the origin is unknown. Finally, it is probable that all bodies are slightly radioactive, and that those at the surface of the ground render the air around them a conductor of electricity.
Time-Constants that Characterize the Disappearance of Emanations and of Induced Radioactivity.—We have seen that the radioactive emanations and the induced radioactivity of solids disappear spontaneously, and that the law of their disappearance is, in general, a simple exponential law. The intensity of the radiation,, is given as a function of the time,, by the formula,
0is the intensity of the initial radiation, anda constant. This exponential law is completely defined by the knowledge of a constant of time that may be, for example, the inverse ofin the preceding formula. One may also take as the constant the time necessary for the intensity of the radiation to diminish to one-half.
It is very remarkable that these constants of time seem to be invariable under widely different circumstances. Thus it is that the emanation from radium diminishes to one-half during each period of four hours, whatever may be the conditions of the experiment, and whatever the temperature between -180° and +450°. The rate of its disappearance is the same whether the emanation be in the gaseous state (room temperature) or condensed (-180°). The properties of the emanation from radium thus give us an invariable standard of time which is independent of all agreements as to the unit.
The time-constants of the radioactivity serve to characterize in a precise manner the nature of the different radioactive energies.
The following are the times necessary for the activity to fall to one-half of its value:
Thus J. J. Thomson and Adam found recently that the emanation from water from certain sources falls to one-half for each period of four days, and that this emanation causes induced activity in solids which falls to one-half in about forty minutes. The supposition is that the emanation contained in the water is due to radium.
Ordinary thorium extracted from monazite sand is slightly radioactive. Thorium from pitchblende is strongly radioactive (thorium with actinium of Debierne). The radioactivity in the two cases is not due to the same substance, for the time-constants of the emanation and of the radioactivity are different.
Certain radioactive substances like actinium have never been separated in a pure state, and it may be supposed that the very active substances that have been studied contain only traces of them. The chemical reactions of substances cannot be recognized with certainty when they are found solely in a diluted condition, mixed with other substances. Under those circumstances one element may carry another down with it in a precipitation, and the action of the reagent is not the same as when we have pure compounds. Hence the chemical reactions will not serve to characterize a radioactive substance. It may, however, be recognized under all circumstances by the time constants of the emanation it emits, and of the induced radioactivity excited by that emanation upon solids.
Nature of the Emanation.—According to Rutherford, the emanation of a radioactive substance is a radioactive, material gas which escapes from it. In fact, the emanation from radium acts in many ways like a gas.
When we put in communication two glass reservoirs, one containing the emanation and the other none, the emanation diffuses into the second and, when equilibrium is established, it is found that the emanation is divided between the two reservoirs according to their respective volumes. One of the two may be heated to 350°, while the other remains at the room temperature, and it is found that in this case, also, the emanation is divided between the two reservoirs as if it were a perfect gas obeying the laws of Marriotte and Gay-Lussac.
We have also seen that the emanation from radium diffuses into the air according to the law of the diffusion of gases, and with a coefficient of diffusion comparable with that of carbon dioxide. Finally, the emanations from radium and thorium condense at low temperatures like liquefiable gases.
At the same time it should be remembered that no one has yet observed any pressure due to the emanation, nor has any one shown by weighing that a material gas is present. All our knowledge of the properties of the emanation results from measurements of radioactivity. More than that, no one has yet shown with certitude that there is a characteristic spectrum produced by the emanation.
The emanation should also not be considered as an ordinary material gas, for it disappears spontaneously from a sealed tube containing it, and the rapidity of its disappearance is absolutely independent of the conditions of the experiment, especially of the temperature.
It is very curious that the numerous attempts made under the most varied conditions to obtain chemical reactions with the emanation have been fruitless. To explain this fact Rutherford thinks that the emanations are gases of the argon family.
The following facts are difficult to explain. The emanation from radium condenses at -150°, and according to Rutherford, a current of air at -153° may be passed over it continuously without removing it. The amount of the emanation must be very small, and if it had the slightest tension at -153°, it would quickly evaporate in a current of air. Further, the temperature of condensation by cooling should be a function of the amount of the emanation in a given volume of air, which has not yet been proved.
Debierne and I have found that the emanation passes with extreme ease through the tiniest holes and fissures in solids, while under the same conditions the ordinary gases could circulate only with the greatest slowness.
Rutherford supposes that radium destroys itself spontaneously, and that the emanation is one of the products of the breaking-down. Debierne and I observed that a solid salt of radium quite rapidly excites the walls of the reservoir filled with air, which contains it, by the emanation which it emits. On the contrary, if a quite perfect vacuum be made in the reservoir the excitation takes place only with extreme slowness; but it rapidly reappears when a gas has been admitted. However, the emanation spreads much more rapidly in a gas at very low pressure than at the atmospheric pressure. It seems from this that the emanation experiences some particular difficulty in escaping from radium which is in a vacuum.
Disengagement of Gas by the Salts of Radium. Production of Helium.—Giesel noticed that solutions of radium bromide continually give off gases. These gases are principally hydrogen and oxygen, in the same relative proportion as in water, and might, therefore, come from the decomposition of the water of the solution. But Ramsay and Soddy also showed that there always is a small quantity of helium that they detected by its spectrum in a Geissler tube. The helium lines were also accompanied by three unknown lines.
A solid salt of radium also constantly gives off gases capable of producing a pressure in a closed tube. To this liberation of gas can be attributed two accidents during my experiments. A sealed bulb of thin glass, almost filled with well-dried bromide of radium, exploded and became slightly warm at the same time. An explosion was also caused by dry radium chloride when heated quite rapidly in a vacuum to 300°. In this case the explosion seemed to be caused by fragments of the solid salt filled with occluded gas.
At the moment we dissolve in water a solid salt of radium that has been prepared a long time, there is an abundant evolution of gas.
The spontaneous production of helium in a sealed tube containing radium is plainly a new fact of fundamental importance. Ramsay and Soddy accumulated some of the emanation from radium, and enclosed it in a Geissler tube at low pressure. They obtained new lines which they attributed to the emanation, and they also showed that the spectrum of helium was absent at first, but that it came into being little by little in the tube. According to that, helium must be one of the products of the disintegration of radium.
In support of the preceding results may be mentioned some points noticed by Mme. Curie and me at the beginning of our work. We were struck by the simultaneous occurrence of uranium, radium, and helium in the same mineral. We took 50 kilograms of commercial barium chloride, coming from minerals that did not contain uranium, and submitted it to fractional crystallization to see whether it contained traces of radium chloride. After a prolonged fractionation, the portion at the head, now reduced to a few grams, was not at all radioactive. Hence, barium contains radium only when it comes from uranium minerals. These are the same that contain helium. One might think that there is a relation of cause and effect from the simultaneous occurrence of these three substances.
This rapid summary of the researches on radioactivity serves to show the importance of the scientific movement that has been started by the study of this phenomenon. The results obtained are of a nature to modify the ideas one might have about the invariability of the atom, the conservation of matter and of energy, the nature of the mass of bodies, and the energy spread through space. The most fundamental questions of science are thus brought into the discussion. Apart from the theoretical interest of which they are the object, the phenomena of radioactivity give new means of action to the physicist, the chemist, the physiologist, and the physician.
Radiation from Uranium.—Becquerel: Compt, rend., 1896-7, different notes; Mme. Curie:Ibid., April, 1898; Rutherford: Phil. Mag., 47, 109 (1899).
Radioactive Minerals.—Mme. Curie: Compt. rend., April, 1898.
Radiation of Thorium.—Schmidt: Wied. Ann., 65, 141; Mme. Curie: Compt. rend., April, 1898; Rutherford: Phil. Mag., 47, 109 (1899); Owens:Ibid., Oct., 1899.
Radiation of Polonium.—P. Curie and Mme. Curie: Compt. rend., July 18, 1898; Mme. Curie: Rev. Gen. des Sciences, Jan. 30, 1899; Mme. Curie: Compt. rend., Jan. 8, 1900. Thèse de doctorat, June, 1903; Becquerel; Compt. rend., 129, 1230; 130, 979, 1154; Merckwald: Ber. d. chem. Ges., June and Dec., 1902; Becquerel; Compt. rend., April 27, 1903 (α-rays), and Feb. 16, 1903.
Radium.—P. Curie, Mme. Curie and Bémont: Compt. rend., Dec. 26, 1898.
Atomic Weight of Radium.—Mme. Curie: Compt. rend., Nov. 13, 1899, Aug., 1900, July 21, 1902; Thèse de doctorat, 1903; Phys. Ztschr., 1903, p. 456.
Spectrum of Radium.—Demarcay: Compt. rend., Dec., 1898, Nov. 1899, July, 1900; Giesel: Phys. Ztschr., Sept. 15, 1902; Runge and Precht:Ibid., 4, 285 (1903).
Radiation of Radium.—M. and Mme. Curie: Compt. rend., Nov., 1899, Jan. 8, 1900, pp. 73 and 76, March 5, 1900 (electric charge of the rays), Feb. 17, 1902 (conductivity of liquids under the influence of the rays); Becquerel:Ibid., Dec. 4, 11, and 26, 1899, Jan. 29, Feb. 12, April 9 and 30, 1900; Giesel: Wied. Ann., 69, 91, 834; S. Meyer and V. Schweidler: Acad. de Vienne, Nov. 3 and 9, Dec. 7, 1899; Kaufmann: Nachrichten der K. Ges. Wiss. Göttingen, 1901, Heft 2; Rutherford: Phil. Mag., 4, 1 (1902).
α-Rays of Radium.—Rutherford: Phil. Mag., Feb. 1903; Becquerel: Compt. rend., Jan. 26, Feb. 16, June, 1903; Des Coudres: Phys. Ztschr., June 1, 1903; Crookes: (spinthariscope) Chem. News, April 3, 1903.
Heat Given Off by Radium.—P. Curie and Laborde: Compt. rend., March 16, 1903; P. Curie: Roy. Inst. June 19, 1903.
Actinium.—Debierne: Compt. rend., Oct. 16, 1899, April 2, July 30, 1900; Feb. 16 and March 16, 1903.
Radioactive Lead.—Giesel: Ber. d. chem. Ges., 34, 3779 (1901); Hofmann and Strauss:Ibid., 33, 3126 (1900).
Radioactivity of all Substances.—Strutt: Phil. Trans., 1901; Phil. Mag., June, 1903; MacLennan and Burton:Ibid., June, 1903; Lester Cooke:Ibid., October, 1903.
Induced Radioactivity and the Emanation of Radium.—P. Curie and M. Curie: Compt. rend., Nov. 6, 1899; P. Curie and Debierne:Ibid., 1901 (5 notes); P. Curie:Ibid., Nov. 17, 1902, Jan. 26, 1903; P. Curie and J. Danne:Ibid., Feb. 9 and June 2, 1903: Dorn: Abhand. Naturforsch. Ges. Halle, June, 1900: Rutherford: Phys. Ztschr., April 20, 1901, Feb. 15, 1902; Rutherford and Miss Brooks: Chem. News, April 25, 1902; Rutherford and Soddy: J. Chem. Soc. (London), April, 1902; Rutherford: Phys. Ztschr., March 15, 1902, Phil. Mag., Nov., 1902, Jan., 1903; Rutherford and Soddy: (condensation of the emanations) J. Chem. Soc. (London), Nov. 19, 1902. Phil. Mag., May, 1903.
Induced Radioactivity and the Emanation of Thorium.—Rutherford: Phil. Mag., Jan. and Feb., 1900; Phys. Ztschr., April 20, 1901; Rutherford and Soddy: J. Chem. Soc. (London), April, 1902; Phil. Mag., 1902, pp. 370, 569; Rutherford: Phys. Ztschr., Feb. 15, March 15, 1902, Phil. Mag., Nov., 1902, Jan., 1903.
Radioactivity and Ionization of the Atmosphere and of Spring Water.—Elster and Geitel: Phys. Ztschr., 1900, 1901; Wilson: Proc. Roy. Soc. (London), 1901; Rutherford and Allen: Phil. Mag., Dec. 24, 1902; Elster and Geitel: Phys. Ztschr., Sept. 15, 1902; MacLennan: Phil. Mag., 5, 419; MacLennan and Burton:Ibid., June, 1903; Saake: Phys. Ztschr., 1903; Lester Cooke: Phil. Mag., Oct., 1903; J. J. Thomson: Conduction of Electricity through Gases, Cambridge, 1903.
Gases Given Off by Radium.—Giesel: Ber. d. chem. Ges., 36, 347 (1903); Ramsay and Soddy: Phys. Ztschr., Sept. 15, 1903.
Physiological Effects of the Becquerel Rays. Action on the Epidermis.—Walkhoft: Phot. Rundschau, Oct., 1900; Giesel: Ber. d. chem. Ges., 33; Becquerel and Curie: Compt. rend., 132, 1289.Action on the Eye.—Giesel: Naturforscherversammlung, 1899; Himstedt and Nagel: Ann. Phys., 4, 1901.
Physiological Action.—Aschkinas and Caspari: Ann. Phys., 6, 570 (1901); Danysz: Compt. rend., Feb. 16, 1903; Bohn:Ibid., April 27 and May 4, 1903.Treatment of Lupus.—Danlos: Soc. Dermatologie, Nov. 7, 1901; Hallopau and Gadaud:Ibid., July 3, 1902; Blandamour: Thesis, Faculty de Médecine de Paris, 1902.
TRANSCRIBER'S NOTEThe cover image was created by the Transcriber and placed in the public domain.
TRANSCRIBER'S NOTE
The cover image was created by the Transcriber and placed in the public domain.