L. Active Modifications of Hydrogen and Nitrogen produced by [alpha] rays. By F. EL Newman, M.Sc, Ph.D., Head of the Physics Department, University College, Exeter [Communicated by the Author.]. 1. Introduction. IT has been shown recently t that nitrogen and hydrogen are both absorbed in the electric discharge tube, in the presence of various elements, when an electric discharge passes through the gases. This effect is due, in part, to chemical action, and is greatest when the element under investigation is deposited on the cathode of the tube. The chemical action appears to be produced by the gases assuming active modifications when an electric discharge is 456 [header] passed through them. Strutt [citation redacted] found that nitrogen drawn from a discharge tube had active properties, and concluded from his experiments that the modified form was atomic in composition. Wendt [citation redacted] has sho n that a modified form of hydrogen, probably consisting of H 3 , is produced when an electric discharge passes through hydrogen at low pressures. In both cases the active form is not due to the ions produced. The radiations from radioactive bodies, and especially the [alpha] rays, produce marked chemical effects in many substances. In general, the chemical actions produced resemble those due to the silent electric discharge. In some cases complex molecules are dissociated, in others more complex molecules are built up. Thus ozone is produced from oxygen. Carbon dioxide is transformed into carbon, carbon monoxide, and oxygen. Carbon monoxide is decomposed with the appearance of solid carbon and oxygen. Ammonia is changed into nitrogen and hydrogen, and in all cases the chemical action is proportional to the amount of radioactive body present, showing that the transformation of each atom of the radioactive body produces a definite chemical effect. It would be expected that the effect of the rays from any radioactive substance, more particularly the [alpha] rays, would be similar to the electric discharge at low pressure. It should be possible to produce the active forms of hydrogen and nitrogen by the [alpha] rays. The object of the present work was to " activate" these gases in this manner, and show by the formation of chemical compounds that the modified form of the gas is more active, chemically, than the ordinary gas. 2. Description of Apparatus. The apparatus used is shown in fig. 1. The gas was prepared, and stored in a very pure condition in a reservoir from which it could enter D. The latter was a known volume (0'106 c.c.) enclosed between two taps. A was the experimental bulb containing the radioactive substance — an electrolytic deposit of polonium on the plate G. The support of the plate was sealed through a glass stopper. The polonium could thus be removed while the bulb A was being cleaned after each experiment. The element used was introduced by the side tube B. The whole of the apparatus was evacuated by a Toepler pump. F and E were [header] 457 entrance and exit tubes respectively for moist air, used in the detection of chemical compounds produced. As a rule, the active gases will not react with any element unless the [figure redacted] surface of the latter is clean and free from occluded gas. In all experiments a thin film of the substance being tested was deposited over the surface of A by distillation in vacuum. The volume of A was about 50 c.c. 3. Experiments with Nitrogen. The nitrogen used was prepared by warming a solution of sodium nitrite and ammonium chloride. The gas was then passed over sodium-potassium alloy, calcium chloride, and phosphorus pentoxide to the reservoir. The whole of the apparatus was thoroughly washed out with nitrogen. The gas was then pumped out, and the element at the bottom of A heated to produce the pure deposit on the interior of A, care being taken that there was no film formed on G. Again the apparatus was evacuated, and the gases liberated by the melting of the element were removed. The tap H being closed, the oil manometer C was calibrated by admitting known volumes of gas from D, the pressure before and after the gas was admitted being noted. The [alpha] rays then acted on the gas in A, producing active nitrogen which combined chemically with the element present. As a result the gas gradually disappeared, this absorption being shown by a gradual decrease in the pressure indicated by C. From the initial and final readings of C the amount of gas absorbed could be calculated. This was repeated, using different, pressures of gas. The polonium was never more than 6 cm., away from any part of A, and the range of the [alpha] rays was always greater than this distance, at the pressures used. The latter were measured by a mercury gauge, not shown in the diagram. 458 [header] The substances selected, were those which are fairly volatile in vacuum. The temperature of the experimental bulb A was maintained at —40° C. by immersion in a freezing mixture. Table I. shows that the rate of absorption increased as the pressure of the gas increased. The chemical Table I. Substance. Volume of nitrogen (at 760 mm. pressure) absorbed in 30 mins. Pressure 3mm. Hg. Pressure 96 mm. Hg. Pressure 304 mm. Hg [table redacted] effect due to the [alpha] rays, which is not necessarily equivalent to the ionization and probably exceeds the latter, appears to be a function only of the velocity of the [alpha] rays and of the number of collisions with the gas molecules. As the pressure decreases, the number of molecules present decreases, and as a result the amount of chemical action decreases. After absorption had occurred no gas was re-liberated when the bulb A was heated to 100° C. The chemical compounds produced must be fairly stable. The disappearance of the gas continued for many hours, but the rate of the absorption decreased with time, and finally ceased altogether. If the substance was re-heated, so that a fresh surface was prepared, the absorption re-commenced. The chemical compound produced at the surface of the substance protects the solid from further action, and accounts for this fatigue effect ; unless the surface under examination was very clean there was no absorption at all. When about 3 c c. of the gas had been absorbed by the sodium-potassium alloy, moist air was drawn through the bulb A from F to E, and was then passed through Nessler's solution. The presence of ammonia in the stream of air showed that the nitrides of sodium and potassium had been produced. A null experiment indicated that this ammonia was not present as an impurity in the air. The product obtained with magnesium was boiled with caustic potash, and the formation of a nitride was shown by the [header] 459 ammonia test. Negative results were obtained with sulphur, iodine, and phosphorus when tested for nitrides. The absorption cannot be due to occlusion, otherwise the gas would have been re-liberated on heating. The effect must be due, in some cases at any rate, to chemical action. 4. Experiments with Hydrogen. The gas was prepared by the electrolysis of barium hydrate. After passing over sodium-potassium alloy to remove any oxygen, and then over phosphorus pentoxide, it was stored in a reservoir. Experiments were conducted in the same manner as those with nitrogen, but it was found that the gas was absorbed only by sulphur, phosphorus, and iodine. The results obtained are shown in Table II. The bulb was maintained at -40° C. Table II. Element Volume of hydrogen (at 760 mm. Pressure) absorbed in 30 mins. Pressure 5 mm. Hg. Pressure 101 mm. Hg. Pressure 299 mm. Hg. [table redacted] The rate of absorption decreased with time, and on heating the bulb to 100° C. most of the hydrogen which had been absorbed was re-liberated. This behaviour is different to that in the case of nitrogen. This indicates that with hydrogen the effect is either due to occlusion, or if it is due to chemical action, the resulting compounds must be unstable. To show that the disappearance of the gas was due to chemical action, the apparatus shown in fig. 2 was utilized. Two strips of platinum foil, about 8 cm. long and fitting close to the interior of the glass tube, were introduced at B. The strips were connected to the terminals of a 600-volt water battery. Any ions present in the gas were removed as they passed through B. Sodium-potassium alloy was prepared in D, and, after the whole apparatus had been exhausted, the alloy was run into C. As a result, the alloy in C had a bright, clean surface. Hydrogen was then drawn through the apparatus, and was subject to the action of the [alpha] rays. When examined by a microscope, the surface at C was seen to be covered with a white crystalline substance, which afterwards changed into a blush-grey coloured film as 460 [header] more hydrogen was drawn through. The experiment was repeated without the polonium present, and in this case the surface of the alloy remained quite clear. The film produced is due to chemical action of the active hydrogen on the alloy. The white crystalline compound appears to be a mixture of the hydrides of sodium and potassium, while the bluish-grey coloured product afterwards formed is probably a solution of these hydrides in the alloy. [figure redacted] For the investigation of sulphur, a film of this element was deposited over the interior surface of C by distillation in vacuum. D contained some filter-paper soaked in lead-acetate solution, together with a little of the solution. After hydrogen, subject to the action of the [alpha] rays, had been drawn over the sulphur for about 30 minutes, the filter-paper in D became blackened. This indicated the presence of hydrogen sulphide in the stream of gas, and it had been produced by the action of the active hydrogen on the sulphur. A similar result has been found by Wendt and Landauer [citation redacted]. This chemical action is not due directly to the ions present in the gas, for they are all removed by the electrostatic field before coming into contact with the sulphur. 5. Other Experiments. Some radium emanation of strength 57 mg., enclosed in a glass tube, was substituted for the polonium. The thickness of the glass — about 0'5 mm. — absorbed the [alpha] rays but transmitted the other rays. After several hours of test there was practically no absorption of hydrogen or nitrogen by any element : this indicates that the [alpha] rays are the effective ones in the chemical actions observed above. Ultra-violet light was employed instead of the radioactive compound. A quartz-mercury lamp was used as the source of illumination, and the experimental bulb A was of [header] 461 quartz. There was, however, no sign of any activation in either gas. This negative result is explained either by the ultra-violet light not producing active gas, or by the quartz not being sufficiently transparent to those rays which produce the active modification. The amount of gas absorbed was independent of the thickness of the element deposited on the glass surface : this indicates that the chemical action occurs at the surface. The rate of absorption was increased by using a larger surface area of polonium, and was decreased when the temperature of the gas was raised. The activation of the gases thus appears to become greater as the temperature is lowered. 6. Discussion of Results. Langmuir [citation redacted] found that hydrogen and nitrogen at low pressures disappeared in the presence of an incandescent tungsten filament, and he has utilized this fact in the elimination of the last traces of gas in valves, etc. The nitrogen forms a nitride with the tungsten. He accounted for the disappearance of the hydrogen by assuming that the molecules of the gas on impact with the hot filament are dissociated into atoms, and these atoms, at very low pressures, have a clear run to the walls of the vessel, and condense on them. This disappearance is marked at low temperatures. On heating the tube, Langmuir found that part of the gas was recovered. This re-liberated gas he supposes is due to the re-combination of the atoms driven off from the walls of the vessel by the heat. At the pressures used in the present work, it is unlikely that the active gas consists of atoms. It is probably dissociated at first into atoms by the action of the [alpha] rays, and the atoms then unite with neutral molecules to form triatomic molecules. The existence of these triatomic forms of nitrogen and hydrogen has been shown by Wendt, in the papers previously quoted, by passing electric discharges through these gases at low pressures. The function of the ions produced by the [alpha] rays does not appear to assist a chemical action between the gas and the element which does not otherwise take place, for the combination occurs after the ions have been removed. More probably the activity of the gas is due to an atomizing effect of the [alpha] rays on the gas, the active product being monatomic 462 [header] gas. Some of the atoms will be formed at the surface of the element, and will react chemically. Others will be produced in the interior of the gas, and will form triatomic molecules by collision with the neutral molecules. The primary action of the [alpha] rays appears to be the liberation of atoms of high activity. In addition, the rays produce [delta] rays by their motion through gases, and these [delta] rays may also be effective in producing the active modifications. The chemical actions occurring are probably determined by the heat necessary to effect the decomposition of the molecules, and not by the heat required for the final transformations and resulting products. That the [alpha] rays produce active modifications of hydrogen and nitrogen, which in turn are able to react chemically with certain elements, strengthens the view that the disappearance of these gases in an electric discharge tube, in the presence of various elements, is also due mainly to the formation of the active modifications of the gases by the electric discharge. 7. Summary. 1. [alpha] rays from polonium were allowed to act on nitrogen at different pressures in the presence of various elements. Some of the gas was absorbed. 2. The elements tested were sodium, potassium, sulphur, phosphorus, iodine, magnesium, arsenic, mercury, together with the alloy of sodium and potassium. Similar experiments with hydrogen gave absorption with sulphur, phosphorus, and iodine. 3. The absorption of the gas was shown to be due to chemical action resulting in the production of nitrides and hydrides. 4. The chemical activity of the gas is due to an active modification produced by the [alpha] rays. The active form, probably consisting of neutral atoms and triatomic molecules, is not due directly to the presence of ions. 5. The [alpha] rays are the only ones effective from radioactive bodies.