A XOTE OK T H E FORAIATION OF LOIiG-LIVED ACTIVE hlOLECULES I N HYDROGEN SUBJECTED TO THE ACTION O F ALPHA PARTICLES FROM RADOK* BY EDTT-ARD C. TRUESDALE
Introduction Some years ago Duane and Kendtl and Wendt and Landauer? as well as other investigaton thought to have obtained evidence of a long-lived form of active hydrogen, frequently called triatomic hydrogen or “hyzone ” This active form of hydrogen was first produced by the action of alpha-particles from 35 millicuries of radon on hydrogen, and later by several other methods involving various types of electrical discharge in hydrogen, contact of hydrogen with hot platinum surfaces, etc., in nearly all cases at atmospheric pressure. Various reactions based on the supposedly greater reducing power of this active hydrogen as compared with ordinary hydrogen were used as tests of its existence. Of the three most consistent tests, the only one which seemed to respond to all methods of activating the hydrogen was the formation of hydrogen sulfide by the action of the triatomic hydrogen on a deposit of sulfur located at some distance downstream from the point of activation of the hydrogen, The other two tests referred to were the reduction of silver nitrate and of potassium permanganate solutions. However, it has been found that ordinary hydrogen will reduce silver ions in the presence of silica gel3 or of filter paper.4 so that the first of these reactions loses some of its significance; the reduction of permanganate solution by hydrogen has been found by Just and Kaukoj to proceed to a sufficient extent to be made the subject of a reaction velocity study. Hence the reaction with sulfur remains the sole “test” for the existence of active hydrogen of long life.** As shown by the investigations of Bach,6 Paneth,? Paneth, Klever and Peters,s Urey and Smallwood: and others, most of the methods of producing ‘Contribution from the School of Chemistry of the Enivewity of Minnesota. W. Duane and G. L. Wendt: Phye. Rev., (2) 10, 117 (1917). * G. L. Wendt and R. S. Landauer: J. Am. Chem. Soc., 42. 930 (1920); 44, 5 1 0 (1922). This aper includes a bibliography of related work. Latshaw and L. H. Reyerson: J. Am. Chem. SOC.,47, 610 (1925). ‘E. C. Truesdale: Intl. Eng. Chem., Anal., Ed., 2, 299 (1930). 6G. Just and I. Kauko: 2. physik. Chem., 76, 601 (1911). ** A copy of a paper by Prof. M. W.Mund has come to the author’s attention since the resent paper was submitted. (“Les Formes actives des Elements,” extract from the k s t i t u t e International de Chimie Solvay, 3e Conseil de Chimie, April, 1928, 86-89.) He states that he has failed to confirm both the contraction in volume ofgy$:$,d due to the formation of Ha from H2, and the formation of mercury hydride, two tests which had been claimed as evidence for the formation of triatomic hydrogen under the influence of abha- article bombardment. bX.Bach: Ber., 58, I388 (1925). This aper also includefi a good bibliography. 7 F. Paneth: Z. Electrochemie, 30, 504 24) BF. Paneth, I. Klever and K. Peters; 2. Elektrocbemie, 33, 102 (1927). H. C. Urey and H. M. Smallwood: J. Am. Chem. SOC.,50, 620 (1928).
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this active form of hydrogen also involved the heating of some metallic surface, or the bombardment of a large glass surface by ions, as in an ozonizer. However, since hydrogen sulfide was formed with or without the presence downstream of the sulfur deposit, and since there was generally a fatigue effect observable in connection with the production of hydrogen sulfide, it seems to be well established that the sources of hydrogen sulfide were sulfur compounds adsorbed on the various surfaces. Moreover, Paneth, Klever and Peters8 failed to repeat the formation of hydrogen sulfide observed by Duane and Kendt, using very small quantities of polonium or of thorium X and C. With the more than zoo millicuries of radon available a t this institution it mas decided to repeat the work of Duane and Wendt to test the question of the existence of the active hydrogen, and to see whether, with the high concentration of ions obtainable, reaction could be produced between the ions and the sulfur a short distance downstream. The various considerations may be stated as follows. When both positive and negative ions in a system are molecular, a , the coefficient of recombination of ions has a value of about 1.6 x IO+. But since hydrogen shows no tendency to form negative ions,1o the negative carriers must be electrons or else, what is more probable, negative ions formed by the impurities present in the system. If it were true that the hydrogen contained no impurities, one might then expect that the value of the recombination coefficient for hydrogen would be very much smaller. Assuming a supply of zoo millicuries of radon, there will be 1.36 x 1 0 1 3 ion pairs formed per second per cc. in a bulb 3 cm. in diameter.” According to the usual method of calculation,‘? if we assume a equal to 1.6 x IO-+ the steady state concentration of ion pairs is found to be nearly 3 X 1 0 9 per cc. I t has been found possible to detect 1.4 X IO-^ gram of hydrogen sulfide4 corresponding to the formation of 7 X 109molecules per second over a period of a one-hour test. Hence even if all the hydrogen ions present in the above steady state concentration were to react with sulfur at the instant of leaving the ionization chamber, the formation of hydrogen sulfide could not be detected in a one-hour test with the hydrogen flowing at a rate of 1 2 0 cc. per minute. Moreover, if we choose an interval of 0.1second between the time the ions leave the ionization chamber and the time when they react with the sulfur, calculation shows that with zoo millicuries of radon we would need to have a value of a equal to 1.6 x IO-^ in order to give a detectable reaction. No justification for such a small value seems to exist, since experimental results have always yielded a value of CY of the order of IO^. I n spite of all precautions in purifying electrolytic hydrogen, one could not safely assert that there might not be one hundred-millionth of one per cent of impurity present, i.e. 1 0 9 molecules of oxygen per cc; this amount of impurity would account for a normal recombination rate. However, since both points of interest could be t,ested a t once, it seemed worth while to conduct l o L. B. Loeb: “The Kinetic Theory of Gases”, pp. 507-513 (1927);also Proc. Nat. Acad. Sei., 6,435 (1920);Phil. Mag., 43,229 (1922). l1 S. C. Lind: “The Chemical Effects of Alpha Particles and Electrons,” 95 (1928). l2 J. J. Thomson: “Conduction of Electricity through Gases”, pp. 27 et seq. (1929).
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the experiments. Moreover, the relatively small surface of the 3 cm. bulb in which ionization occurs, and the relatively long duration of the experiments practically insures freedom from the fatigue effects peculiar to other methods of activation. Preliminary experiments using 164 millicuries of radon in a thin-walled alpha-ray bulb, and employing a purification train for the hydrogen containing solutions of potassium permanganate, potassium hydroxide, and sulfuric acid along with other customary features, indicated that there was no formation of hydrogen sulfide due to the presence downstream of purified sulfur. A very faint marking on the lead acetate paper used in making the test which appeared when the hydrogen was passed through the ionization sphere and onto the sulfur, but which was absent when the radon bulb was by-passed, indicated that a trace of some sulfur compound was present which reacted with hydrogen in the ionization sphere to produce hydrogen sulfide. It was thought that this impurity probably came from the sulfuric acid. Accordingly several changes were made in the system.
Experimental Hydrogen was prepared by the electrolysis of a thirty per cent solution of potassium hydroxide which contained a slight excess of barium hydroxide. The generators, of which there were four, were of the common “sleeve” type in which the electrodes, which were coils of pure nickel wire, were placed inside and outside of a 5 cm. glass tube which was immersed in the solution; each assembly was contained in a suitably stoppered 4-liter bottle. The hydrogen was liberated a t the inner electrode. These sleeves were part of an all-glass system which was connected to the purification train by means of a three-way stopcock. The current was varied from 3 to 5 amperes a t I I O volts. I n some of the experiments tank hydrogen was used in order to increase the rate of flow, the same purification train being used in all cases. The final purification train consisted, in order, of a tube 30 cm. long on the inner surface of which had been deposited by fusion in a vacuum some potassium hydroxide containing a trace of potassium permanganate; an electrically heated tube I O O cm. long containing copper made active by repeated oxidation and reduction of copper oxide wire; two tubes similar to the first but containing only fused potassium hydroxide; two tubes 2 j cm. long, on the walls of which phosphorus pentoxide had been sublimed in a current of oxygen a t a pressure of I cm; finally, a liquid air trap. The system was connected to the mercury pump and pressure gauge through a stopcock which was protected on both sides by liquid air traps. Magnetic valves were provided by means of which the radon bulb and also the sulfur deposit could be by-passed; thus the only “unprotected” stopcock in the system was that through which the hydrogen came from the electrolytic generators. A mercury trap was provided near the outflow end of the system to facilitate evacuation and flushing out of the system, protection from mercury vapor being provided for by a liquid air trap just preceding this mercury column. The
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radon was contained in a tiny alpha-ray bulb located a t the center of a 3 cm. bulb which was itself 13 cm. distant from the deposit of sulfur. The sulfur used had been distilled twice in air, twice in a current of carbon dioxide, and finally fractionated five times a t a pressure of 4 mm. of mercury. The final fractionation placed the sulfur in a bulb provided with side arms containing sealed-in tips; upon completion of the distillation the bulb was sealed off from the distillation system, and by means of the side tubes was sealed into the experimental system. Thus the sulfur was kept under vacuum until the moment it was wanted in the system, when by means of a magnetic breaker the tips were broken and hydrogen was admitted. hydrogen ni
FIG.I Reaction System
The presence of hydrogen sulfide was detected by delivering the gas through a capillary tip in a fine stream against a strip of quantitative filter paper moistened with an alkaline solution of lead acetate. A tiny glass guard prevented the paper from touching the tip. Such a method has been found to be sensitive to about 10-9 gram of hydrogen sulfide, contained in I O cc. of diluent gas at a concentration of one part in ten m i l l i ~ n . The ~ apparatus was constructed entirely of Pyrex, and the final form of the reaction system is shown in Fig. I . The system was prepared for operation by evacuating as completely as possible, flaming out all possible parts and then, with the stopcock leading to the pumps closed, admitting hydrogen to a pressure of half an atmosphere. This process was repeated three times. Finally the stopcock leading to the pumps was permanently closed and the system filled with hydrogen at a pressure about I cm. greater than atmospheric and flushed out for a total of about ten hours. The liquid air traps and the hot tube containing the reduced copper were maintained in continuous operation until the end of the
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experiments, with the exception of the liquid air trap just preceding the testing device which was used only as wanted provided that the hydrogen was streaming through the system, thus preventing mercury vapor from diffusing back into the rest of the system. A quantity of radon measuring 184 millicuries before introduction into the system was put in place, and a few hours later the tests were started. The tests were carried out by putting a strip of filter paper in place and streaming hydrogen against the paper for a given length of time, usually one hour, A given series of runs included tests with and without exposure to the sulfur, and with and without exposure to the alpha-particles, other experimental conditions remaining the same, Le, rate of flow, source of hydrogen, use of liquid air on final trap, etc. The results of some 40 experiments were as follows. Results I n nearly all tests an extremely faint marking appeared on the paper just opposite the tip of the capillary. These markings were always more evident when the hydrogen was exposed to the action of the radon than when it was not, but were in no way related to the presence or absence of the sulfur in the hydrogen stream. Even the heaviest of these spots was just barely visible and all such spots faded or disappeared over intervals varying from a few minutes to a few hours after removal of the papers from the tester. All papers were kept in a desiccator, some of them in air and some in hydrogen, such change in environment having no effect on the fading. This behavior remains unexplained, but is not considered to vitiate the results because of the following facts. Sone of these spots was as distinct as, nor had a similar appearance to spots obtained in tests where as little as IO+ gm. of hydrogen sulfide was known to be present. Further, such spots known to be due to hydrogen sulfide did not fade when kept for days, and were of a light brown color, whereas the spots obtained in the radon experiments were of a very faint gray color. I n fact some of these “spots” that faded were thought to be due to evaporation of water from the paper just opposite the capillary tip in the rapid stream of hydrogen, thus producing a change in the transparency of the paper at that point. Firtally the system was opened, and less pure sulfur was introduced into the hydrogen stream a t points closer to the radon but still out of the path of the alpha-particles. There was then no indication of the formation of hydrogen sulfide. Tank hydrogen was also used, in order to increase the rate of flow and shorten the interval between activation of the hydrogen and contact with sulfur. No difference was observed due to the use of tank hydrogen, nor to the increase in the rate of flow. The sulfur deposit was originally located a t a distance of 13 cm. from the ionization sphere, and with this arrangement the times of mixing were 2.4, 1.8 and 0.4 seconds, corresponding to rates of flow of 80 120, and 550 cc. per minute. The shortest mixing time
LOSG-LIVED ACTIVE ?JOLl
