391 i Experiments upon the Reported Transmutation of Mercury into Gold. By M. W. Garrett. B.A., Exeter College, Oxford. (Communicated by Prof. F. A. Lindemann, F.R.S.—Received July 14, 1926.) The possibility of effecting a transmutation of the atom by electronic bom­ bardment, as distinct from the alpha-ray methods so successfully used by Rutherford and others, has attracted attention from time to time in recent years. The first to report success in such an experiment was Ramsay, who announced in 1912 the artificial production of helium and neon in X-ray bulbs. The controversy aroused by his announcement has not yet subsided, for Riding and Baly have supported quite recently, in this Journal, the genuineness of such a transformation. Miethe,* in 1924, reported the transmutation of mercury into gold, and since the original announcement he has described various experimental arrange­ ments which he claims have proved successful.*)* Two principal methods have been employed by this investigator. First, a Jaenicke mercury vapour lamp, operating at atmospheric pressure with a current of 12*5 amperes, a terminal voltage of 170, and a potential gradient of 11 or 12 volts per cm., was run for 20 to 200 hours, and amounts of gold up to 0*1 mg. reported, though no direct proportionality existed between the quantity of gold and the number of hours run. Miethe also reported the formation of silver in these experiments, often in larger amounts than the gold, and stated that the yield of noble metals was increased by irregular burning of the arc, with frequent extinction and relighting. No gold was obtained from vacuum arcs. The second method was a development of the first, in which the effect of irregular burning was arti­ ficially enhanced by constant interruption of the arc. The final simplified form of this experiment consisted in the employment of an ordinary rotating mercury interrupter, and with this apparatus Miethe states that he obtained for the first time consistently reproducible results, a direct proportionality existing between the number of ampere hours run and the yield of gold (about 4 X 10~7 gm. per ampere hour.) He also describes a series of experiments in which one and the same quantity of mercury (ca. 1*5 kg.) was submitted to a number of successive runs, about a score in all, when no diminution of the * ‘ Naturw.,’ vol. 12, p. 597 (1924); 4Nature,’ vol. 114, p. 197 (1924). t Stammreich, 4Naturw.,’ vol. 12, p. 744 (1924); Miethe and Stammreich, 4Naturw.,’ vol. 13, p. 635 (1925); 4 Z. techn. Phys.,’ vol. 6, p. 74 (1925); 4Z. anorg. Ch.,’ vol. 150, p. 350 (1926). VOL. CXII.—A. 2D 392 M. W. Garrett. yield was observed. He states that self-inductance was here found to be absolutely without effect, though from certain earlier experiments he had believed that the inclusion of an inductance in the circuit increased the yield. No mention is made of the production of silver in these experiments. Nagaoka,* working quite independently, used an induction coil capable of giving a spark of 120 cm. length. With a capacity of 0*002fx F in parallel and a secondary current of 10 ma. he sparked for four hours between a tungsten pole and a mercury surface under transformer oil, until the entire mass car­ bonised. He then tested for gold by methods which, though they could give no quantitative idea of the amount present, seem to have been qualitatively reliable, and he states that all the tests were unmistakably positive. In a second, somewhat different, experiment he found mainly silver. It seemed worth while to make some attempt to confirm or refute these experiments, more especially since there appeared, shortly afterwards, an announcement by Smitsf that he had succeeded in transmuting lead into thallium and mercury by a somewhat similar method. When the work described in this paper was undertaken, only the positive results outlined above were extant. Since then, no further positive results have been reported, whereas negative results have been announced by various experimenters^ operating under diverse conditions. Of these the work of Haber is the most complete, as well as the most recent. In some cases the published papers contain so few^ details of experimental conditions, duration of the runs, and analytical methods, that it is difficult to draw any conclusions from them. A general discussion of the various results will be postponed until after the description of the experimental work carried out by the writer has been completed. E x per im en ta l . Distillation of the Mercury. The mercury employed in these experiments was taken from a single stock prepared by two successive distillations and kept in a glass-stoppered bottle. * 4Naturw.,5 vol. 13, p. 682 (1925), and vol. 14, p. 85 (1926); 4Nature,5 vol. 116, p. 95 (1925); 4J. Physique et Ra.,5 vol. 6, p. 209 (1925). t 4Naturw.,5 vol. 13, p. 699 (1925); 4Nature,5 vol. 117, p. 13 (1926). (An examination of the results of Smits is now in progress, and it is hoped to be able to report upon it, as well as upon certain related work, in the near future.) J Sheldon and E stey,4Sci. Amer.,5p. 296 (Nov., 1925), and p. 389 (Dec., 1925); 4Nature,5 vol. 116, p. 792 (1925); Tiede, Schleede and Goldschmidt, 4Naturw.,5 vol. 13, p. 745 (1925); Piutti and Boggio-Lera, 4Rendic. Accad. Sci. Fis. Mat.5 (Naples) (Sept.-Dee., 1925); 4Nature,5 vol. 117, p. 604 (1926); Haber, Jaenicke and Matthias, 4Naturw.,5 vol. 14, p. 405 (1926); 4Z. anorg. Ch.,5 vol. 153, p. 153 (1926). Reported Transmutation of Mercury into Gold. 393 Two identical stills of Pyrex glass were employed, one for each stage of the dis­ tillation. These were of ordinary design, consisting of a wide inverted U-tube and two narrow limbs of barometric height dipping into reservoirs of mercury. When once exhausted, baked out and sealed, they were quite continuous in operation, it being necessary only to pour the mercury into one side and draw it off from the other. They were electrically heated by means of nichrome coils of high resistance, so that only 50 watts were expended in heating in each still, and in spite of the wide tubes (3 cm.) and water cooling, the rate of distillation was only about 100 gm. per hour. Under these circumstances the temperature of the mercury did not rise much above 150°, and evaporation took place quietly from the surface. Since the whole of the input side of the still was heavily lagged with asbestos cord, any particles which might be situated in the free space above the mercury were not subjected to any unnecessarily heavy differential molecular bombardment from below (as in a mercury vapour pump), and there was no tendency for surface impurities to be mechanically carried over with the vapour. These details are mentioned here because of the fierce (and somewhat point­ less) battle which has been waged over the question of whether the noble metals are completely removed from mercury by distillation. This question is of some interest in itself, but its importance to the transmutation controversy has been greatly over-estimated. For Miethe has regularly analysed his mercury after its electrical treatment by the same process which he employed before it, and his blank experiments have been invariably negative. The question of whether distillation removes all traces of gold is thus clearly resolved into the question of whether distillation removes electrically treated gold more efficiently than it does ordinary gold. Nobody has yet attacked this problem experimentally ; or rather this problem is, experimentally considered, practically identical with the transmutation question proper. Hulett, Riesenfeld and Haase, and Tiede have all reported* that gold dis­ tills over in small quantities with mercury, though all except Tiede agreed that two or three distillations even of a strong amalgam were sufficient to reduce the concentration of gold to the extreme limit detectable. Tiede found that under certain conditions the gold actually concentrated itself in the distillate, a sufficiently improbable result which is in want of confirmation. Miethe and Stammreich,f as the result of methodical experiments on the * Hulett, 4Phys. Rev.,’ vol. 33, p. 308 (1911); Riesenfeld and Haase, 4Ber. deutsch. Oh. Ges.,’ vol. 58, p. 2828 (1925); Tiede, ‘ Phys. Z.,’ vol. 26, p. 845 (1925). t 4Phys. Z.,’ vol. 26, p. 842 (1925); 4Ber. deutsch. Oh. Ges.,5 vol. 59, p. 359 (1926); 4Z. anorg. Oh.,’ vol. 149, p. 263 (1925). 2 D2 394 M. W. Garrett. distillation of amalgams of various metals, have concluded that with proper precautions these metals pass over into the distillate only by virtue of their own proper vapour pressure (i.e., in very small amounts, so small as to lie beyond the limits of detection in the case of the noble metals). They believe that where gold is not removed from mercury by a single distillation, the cause is to be sought in small particles of it having been carried over mechanically with droplets of mercury which have reached the receiver without passing through the vapour phase at all. This form of mechanical contamination can be eliminated by careful attention to the design of the apparatus and regulation of the conditions of distillation. They quote Michaelis in support of this view, which is shared by the present writer, and is capable of explaining the results of the other experimenters. Hulett distilled at a pressure of over a centimetre with a stream of air bubbling through the mercury, while the work of Riesenfeld and Haase is fragmentary, and is otherwise open to grave objections which have been pointed out by Miethe. Never in the course of the experiments described below has it been found possible to detect gold in mercury which had been distilled, though in the course of the preliminary analytical practice some moderately strong amalgams were distilled. Analytical Procedure. Methods of analysis have been described by Haber,* and by Miethe and Stammreich.t The method employed in the present research was essentially that of Miethe. This consists in distilling off the mercury till only about one gram remains, and dissolving up this last drop, under the microscope, in nitric acid of specific gravity 1*20, free from all traces of hydrochloric acid. The gold remains behind as metal, and may be estimated by fusing it in borax and measuring the diameter of the resulting sphere. This method of analysis was tested on 100 gm. samples of mercury to which known small quantities of gold had been added, and it was found possible to detect 1CT7 gm., and afterwards, with improved microscopy, 10“8 gm. of gold with absolute regularity. It was also repeatedly proved that no gold could be detected in the stock of distilled mercury when analysed by this method. There can be no ^question that the analysis could have been rendered still more sensitive, but a suitable microscope was not at hand, and it was considered * Haber, Jaenicke and Matthias, loc. cit., and Haber and Jaenicke, 4Z. anorg. Ch.,’ vol. 147, p. 156 (1925). f c Z. anorg. Oh.,’ vol. 140. p. 368 (1924), and vol. 148, p. 93 (1925). Reported Transmutation of Mercury into Gold. 395 that quantities of gold less than 10“8 gm. could have no significance in testing methods said to be capable of producing 10-4 gm. with moderate energy inputs, particularly since the danger of error through accidental contamination becomes quite large when working with quantities below 10-8 gm. All the experiments were so designed as to require minimal quantities of mercury, never more than 100 gm. and rarely as much as 50. It is perhaps unnecessary to add that all the vessels employed in the research had been carefully cleaned with boiling aqua regia. Spark Methods. The first experiments were similar to those of Nagaoka, but with slight modifications. A transformer giving a peak voltage of 15,000 was employed, with a condenser of 0 •006 fi F capacity. The spark was passed between tungsten wires in a glass vessel containing an emulsion of fine mercury drops in white paraffin oil. Miethe, in similar sparking experiments, had always found the gold concentrated entirely in the small droplets of mercury dispersed along the path of the discharge, and the above method, by starting with a fine emulsion, permitted the main mass of inert mercury to be eliminated altogether from the experiment, less than 10 gm. being required for each run. Furthermore, in experimenting on the Stark effect in silver arcs Nagaoka had found that the presence of small droplets resulted in a marked local intensification of the potential gradient. It was found necessary to place the two wires constituting the spark gap less than 2 mm. apart in order to permit the spark to pass, so that although the actual voltage was much below that employed by Nagaoka, the potential gradient remained substantially the same. The gradient is, in fact, determined by the dielectric strength of the oil, and it should be noted that even this initial gradient becomes much reduced as the experiment proceeds and the oil is carbonised. The larger condenser permitted heavier secondary currents (20-30 ma.) to be employed than those used by Nagaoka, and the transformer delivered a much steadier voltage than is obtained from an induction coil. Considerable trouble was experienced with the bursting of the glass vessel and the splashing of the emulsion, and the final form of apparatus employed was a glass tube about 6 cm. deep by 2 cm. in diameter, with a widely flared top ground flat and held against a sheet of ebonite by rubber bands. The tungsten wires were carried by thick-walled glass capillaries inserted through the ebonite. The sparking vessel was water-cooled. It was found possible to run about 396 M. W. Garrett. half an hour before the oil solidified completely and showed a tendency to arc. The mixture of miscellaneous organic matter, mercury and carbon was then transferred to a Pyrex flask and distilled in an electric furnace, when the carbon remained behind. This was oxidised by heating in a stream of oxygen, leaving hardly a trace of residue of any kind. The flask was now washed out with hot aqua regia, the solution diluted, and a small drop of mercury added. When this had dissolved, the solution was make alkaline with ammonia, and the mercury reprecipitated by the addition of ammoniacal 6 per cent, hydrazine sulphate solution. The mercury drop, which would have carried down with it any gold present, was filtered off, washed, and dissolved up as usual, under the microscope, in dilute nitric acid. This experiment was repeated several times, with uniformly negative results. Distilled water was then substituted for the oil, in the hope that it could be made to run longer without losing its insulating properties. Aluminium electrodes were employed, and the emulsion was prepared by passing an arc at 100 volts between an aluminium pole and mercury at the bottom of a beaker of distilled water. But the water always became conducting after 20 minutes to half an hour, and the explosive spark at first produced could no longer be maintained. One lot of mercury in water emulsion was analysed after about 25 minutes’ run, but no gold w^as found. Longer runs and larger energy inputs were found possible when hydrogen was used as the dielectric. The apparatus used is sketched in fig. 1. It was constructed in Pyrex, with a tungsten wire sealed into the bottom to establish contact with the mercury pole. The other pole consisted of a 4 mm. iron rod, clamped by means of a set-screw into a steel tube attached to the copper electrode A. The latter was turned down to a thin tube at its upper end, and sealed directly into the central glass tube carried by the ground joint. This electrode was kept cool by the boiling of water which filled the central glass tube, and the mercury pole was cooled in a similar manner by a vessel of water in which the outer tube was immersed. The apparatus was connected during the experiment to a reservoir of hydrogen, and the ground joint fitted so well Reported Transmutation of Mercury into Gold. 397 that without any lubrication only a few cubic centimetres of hydrogen per hour escaped through it. With a spark gap of about 1 cm. and a capacity of 0*01 p. F, the secondary current of the 15.000-volt transformer was 75 ma., and the current in the spark gap 15-20 amperes. A limit to the useful length of a run was set by the con­ tamination of mercury and glass by fine dust from the iron pole, which burned away at the rate of about half a millimetre an hour, so that the apparatus had to be continually reopened and this pole reset. Two analyses were made on runs with this apparatus, one after five hours and one after twelve. The liquid mercury was mechanically separated from the superincumbent emulsion of finely divided mercury and iron dust; the former was distilled to a residue of 1 gm., and the latter digested with aqua regia until all the mercury had dis­ solved. The residue from the distillation was dissolved in the solution contain­ ing the extract of the emulsion, the mercury precipitated with hydrazine, and the remainder of the analysis proceeded with as usual. The result was negative in both cases. The conditions in such a spark discharge might be expected to be very favourable to the formation of gold. In the first place, it seems highly probable that doubly charged ions of mercury are present; the significance of this fact will be discussed hereafter. The spectrum of this spark showed a very different intensity distribution from that of the mercury vapour lamp, the three lines 6149, 5679 and 5425 being among the strongest on the plate. The light was nearly white except at the iron pole, where it was coloured quite red by a preponderance of the Ha line. In the second place, Miethe concluded, from the irregularity of his early results, that the formation of gold depended upon the exact reproduction of certain conditions of potential gradient and current density, which he was unable to define, but which he assumed his arcs passed through at some stage during the changes accompanying extinction and relighting. Now in an oscillatory discharge such as that here employed, the current varies between a maximum value of several hundred amperes and zero, and the voltage between the limits of 15,000 and zero, so that at some time during the cycle the favour­ able conditions should be reproduced ; and the cycle is repeated 100 times per second. Interrupted Arc Method. A method was now developed which proved capable of giving more decisive results. Miethe has constantly maintained that the earlier forms of experiment which he employed did not yield consistently reproducible results, and has on 398 M. W. Garrett. occasion attributed the failure of other experimenters to this fact. But from the first he has considered the interrupted direct-current arc to be quite reliable, and in particular he has found a reasonable proportionality between energy input and yield of gold when using a mercury interrupter of standard design. It was considered desirable, accordingly, to repeat these experiments in some form, but the objections to the ordinary type of interrupter are considerable. It makes use of large electrodes of copper in a case consisting of enamelled iron or some similar material. It is difficult to ensure that these materials are quite free from gold, and since the electric discharge plays continually over their surface and they are gradually worn away, there is great danger of contamina­ tion from this source. Large quantities of mercury (1*5 kg.) must be used, and the mercury emerges in a very dirty condition from the run, so that the analytical procedure is also rather unsatisfactory. The “ blank ” experiments of Miethe (in which the interrupter ran without current and no gold was found) are not convincing as proof that the gold did not arise by contamination from the electrodes, since in this case there is no sparking at the electrode surfaces. It would be interesting to know whether the mercury did not emerge in a cleaner condition from such a “ blank 55 determination, as might have been expected. To obviate several of these difficulties the construction of an all-glass mercury interrupter, with mercury cups in place of the copper electrodes, was under­ taken. Such an interrupter was actually completed, but it was never used, since a much simpler design was evolved which permitted the use of minimal quantities of material and the removal of the foreign electrodes to a point remote from the discharge, while preserving the essential features of the break. The apparatus consisted of a tube such as that sketched in fig. 2. This was filled with an amount of mercury indicated in the diagram, sealed off in an atmosphere of hydrogen, and fastened to a machine which swung it back and forth in arcs of 50-60° about the point 0, the 100-volt mains being connected to the two ends of the tube. The mercury in the two branches flowed together and then separated twice in every swing, an arc being formed and pulled out to extinction each time. Six or eight interruptions per second were obtained in this way, and the sharpness of the break was attested by the intense condensed spark obtained in the secondary circuit of an induction coil when the break was inserted in the primary circuit. Such tubes were first constructed of Pyrex, with 0-5 mm. tungsten wires sealed into the legs. But the current-carrying capacity of the Pyrex tubes was limited to about 12-15 amperes (at make), and their life to some 60-70 hours. The intense local sparking removed small flakes from the glass surface, which soon became covered with a network of Reported Transmutation of Mercury into Gold. 399 fine cracks, the mercury was slightly contaminated, and the Pyrex in time blackened. A number of tubes burst after some hours’ sparking. Nevertheless, F ig. 2. three runs were obtained with Pyrex tubes, the current at make averaging 13 amperes, and the duration of sparking 55 hours. No gold was found in the mercury from these tubes. A similar tube was now constructed from quartz, as soon as a suitable technique had been developed for making the seals into this material. The 0*5 mm. molybdenum wire to be used was first heated to incandescence in vacuo to remove occluded gases, and the quartz was then shrunk upon the molybdenum, also in vacuo, and the seal completed by means of pure lead and a short length of copper wire. Such seals were always found to be quite vacuum-tight, but as an additional precaution the hydrogen was introduced, after baking out and filling with mercury, at such a pressure that the constriction would only just collapse on sealing the tube off from the pump. This ensured a pressure greater 400 M. W. Garrett. than atmospheric at all times on the mercury at the seal, and particularly when the tube was heated by the arc. It was found possible to operate this tube indefinitely with 30-ampere sparks at 100 volts. The mean current was given as 10 amperes by a thermal junction constructed of 22-gauge copper and eureka wires, mounted in a brass case immersed in water, and calibrated on direct current. * The tube was run under these conditions for 144 hours. It was then operated from a direct-current dynamo, delivering 240 volts in 18 ampere sparks (7 amperes average) for a further 144 hours. During the last 24 hours of this run, the primary of an induction coil was included in the circuit, energy being drawn from the secondary in the form of a condensed spark discharge in air. At the end of this time the quartz tube remained as clear as at the beginning of the experiment, while the mercury surface was perfectly bright and uncontaminated. The tube was, in fact, indistinguishable in appearance from a fresh one. In the analysis of this run, distillation was avoided, on account of the con­ troversy referred to above. Two samples of 15 gm. each were drawn from the stock bottle of distilled mercury. To one of these was added 10~8 gm. of gold. Both samples were dissolved in nitric acid, also ready mixed in a stock bottle. The 10“ 8 gm. of gold was identified without question by several people when the mercury to which it had been added had dissolved. The other sample of mercury left no residue whatever. The quartz tube was now opened and found to contain 18*8 gm. of mercury, which was dissolved up at once in acid from the same stock bottle as had been used for the blanks. It left behind a residue about 0*03 mm. in diameter, consisting of a flattened reticulated skeleton of some dark material, presumably silica. Not a trace of the lustre of metallic gold could be discerned. The blank tests which were carried out simultaneously with this analysis remove all doubt as to the sensitiveness of the test. 10-8 gm. of gold could have been detected with absolute certainty. It is easy to form a rough idea of the amount of gold which should haye been expected in this experiment according to the results obtained by Miethe. If we take the efficiency of the arrangement, expressed in grams of gold per ampere hour, to be the same as that of Miethe’s rotating mercury interrupter, we arrive at an estimate of 1 mg. of gold, an amount larger than that which any experimenter has claimed to produce in a single run. A more accurate estimate is probably obtained by considering the number of “ ampere sparks. ” That is, if Miethe’s view of a “ labile state ” passed through by the arc once in each cycle is correct, an approximately constant amount of gold should be produced each time an arc of 1 ampere is made and extinguished, and Miethe’s Reported Transmutation of Mercury into Gold. 401 own results indicate that the yield is directly proportional to the current for the same number of interrupted arcs ; hence, we arrive at the “ ampere spark ” as the effective unit of gold-producing electrical energy. Assuming now four interruptions per second (a very conservative figure) in the quartz tube, and taking Miethe’s figure of 2,000 per minute for the frequency of interruption in his mercury break, the above estimate is reduced to 0*11 mg., which is still at least 11,000 times the amount of any gold which may actually have been produced. Discussion. There are various theoretical objections to the wrork of Miethe and of Nagaoka. Perhaps the most cogent arises from a consideration of the voltages which they employed in their experiments. In order to bring about a trans­ mutation of the atom, it is first necessary that the bombarding particle—in this case an electron—should penetrate the successive electronic orbits, and gain access to the nucleus. The most obvious method of ensuring this is to make use of electrons of sufficient velocity to excite the hardest K radiation of the element in question. The corresponding voltage, in the case of mercury, is about 83,000, and though Nagaoka employed considerably higher terminal voltages than this, it is impossible that any individual electron could have possessed more than a small fraction of the required velocity ; for the potential gradient in these experiments was about 15,000 volts per millimetre, so that the electron would have to fall freely through the field for a distance of 5*5 mm. in order to attain the velocity in question. The actual free path must have been of quite a different order of magnitude from this, and it is, of course, well known that the K spectra are not excited under the conditions of Nagaoka’s experiment. The highest electronic velocities hitherto applied to the transmutation of mercury were probably those employed by Haber in his experiments with an X-ray bulb whose anticathode consisted of frozen mercury ; but here a voltage of 8,000 was not exceeded. However, the work of Ramsauer* and others on the rare gases indicates that under certain conditions these extreme electronic velocities may not be necessary, for certain atoms show a marked transparency to very low-voltage electrons. Where such a property exists, it is obviously of advantage to use as low a voltage as possible, partly because a slow-moving electron, once safely inside the innermost electronic orbit, might be expected to be more readily attracted into the nucleus than a fast one, but principally because with low voltages it * ; Aon. d. Physik,’ vol. 64, p. 513, and vol. 66, p. 546 (1921). 402 M. W. Garrett. is possible to use much larger currents, and thus by increasing the number of electrons to ensure a greater chance of scoring a hit upon the nucleus. Erode* has examined the mean free path in mercury vapour of electrons possessing velocities between 0*4 and 150 volts, and has found between these limits no indication of any special transparency of the mercury atom ; neither does extrapolation of his curves suggest the existence of any such property at other voltages. Thus it begins to appear doubtful whether any of the electrons in the various transmutation experiments really had access to the mercury nucleus at all. Franck has suggested that doubly charged ions might resemble a rare gas to such an extent as to exhibit transparency to electrons of certain velocities, but an experiment described in this paper, as well as a some­ what similar one performed by Haber, in both of which such doubly charged ions were probably fairly numerous, proved quite as incapable as the rest of yielding gold. We cannot altogether reject the possibility that the electron, once inside the innermost planetary orbit, should be attracted towards the nucleus and might fall into it. This might occur with such violence as to produce disruption of the nucleus ; or, alternatively, the invading electron might be captured and remain permanently attached to the nucleus, thereby giving rise to the inverse of a beta-ray disintegration, and reducing the atomic number by one unit. The latter seems the more likely alternative, though Nagaoka has supported the former. He was led to undertake his experiments by observations on the spectrum of mercury, from which he concluded that the nucleus contained a quasi-elastically bound proton which might be dislodged by bombardment with very swift electrons. But the theory of Nagaoka has been attacked by Rungef and the experimental work by Wood 4 The theory was based, moreover, on a list of the isotopes of mercury, which has since been revised by Aston. If a transmutation of the inverse beta-ray type is to occur at all, the most hopeful case would seem to be that of two neighbouring elements in the periodic table exhibiting isobarism. Unfortunately, Aston’s table of isotopes does not reveal a single established case of such a relation, though the isotopes of gold, lead and thallium, all of which are involved in the reported trans­ mutations, have not yet been established. Honigschmid’s determination of the atomic weight of Miethe’s gold, though a triumph of analytical chemistry, has lost its significance in view of Miethe’s recent statement (at a meeting of * kHoy. Soc. Proc.,’ A, vol. 109, p. 397 (1925). t ‘ Nature,’ vol. 113, p. 781 (1924). X ‘ Nature,’ vol. 115, p. 46 (1925). : « Reported Transmutation o f Mercury into Gold. 403 the German Chemical Society, May 10, 1926) that the gold which he sub­ mitted to Honigschmid for this determination was not actually produced by himself under known conditions, but was obtained from residues found in old mercury lamps. * In the present state of our knowledge of atomic physics, it is difficult to form an estimate of the importance of these theoretical considerations. In the circumstances, therefore, it is perhaps safest to regard the whole question from the purely experimental point of view. When this is done, it is found that the various experimenters have arrived at mutually incompatible conclusions. Further, it seems probable that the cause of the contradiction is not to be sought in a difference in the electrical conditions of the experiments. Granted that the formation of gold is bound up with some one particular set of con­ ditions (potential gradient, current density, etc.), and that these conditions are difficult to reproduce, it may perhaps be argued that no single set of similar experiments leading to negative results is convincing. But when the wide diversity of the experimental arrangements which have failed in the hands of several investigators to produce gold is considered, it appears that every positive experiment has been adequately confuted by a negative one. Miethe has always refused to recognise the validity of any negative results obtained by repeating his own earlier experiments, on the ground that only the interrupted-arc methods are capable of giving consistently reproducible results. He is justified in taking this stand, but the interrupter experiments now appear to be at least as conclusively negatived as any of the rest by one of Haber’s experiments, in which the fluctuating current passed by a rotating mercury interrupter was made to traverse a mercury vapour lamp, and more particularly by the quartz tube experiment described in this paper, where the electrical conditions were to all intents and purposes identical with those existing in the interrupter experiments of Miethe. For it is hardly conceivable that the actual difference in speed of motion of the mercury in the two cases can appreciably affect the electrical conditions, when it is considered that the maximum velocity of the mercury jet in a rotating break is very small compared with the elec­ tronic and even molecular velocities. The abrupt and complete extinction of the arc in the tilting quartz tube was showui by the efficiency of the apparatus as an interrupter for an induction coil, by the small ratio of mean to shortcircuit current, and by the behaviour of an incandescent lamp connected across the terminals of the tube. Even if one admits a slight difference between the electrical conditions in this experiment and Miethe’s, to assume that it could be such as to yield large quantities of gold in the one case and absolutely none in 404 M. W. Garrett. the other is quite inconsistent with Miethe’s own earlier work on continuously burning and interrupted arcs. The explanation of the discrepancy between Miethe’s results and those described in this paper must be sought elsewhere. Much the most probable explanation seems to be that Miethe’s gold was derived from the electrodes or other materials of the vessels used, though this conclusion is not altogether satisfactory, in view of Miethe’s statement that the purity of all the materials he employed was “ dauernd kontrolliert.” Further details of these controls would seem desirable. Perhaps also it is straining a point to attempt to explain in this way the direct proportionality which he obtained between power input and yield of gold, but it is possible, particularly since discrepancies of the order of 40 per­ cent. were found. In this connection it is significant that the method which has given the most consistently reproducible results is one which is so con­ spicuously untidy that only the most rigid proof will serve to eliminate the suspicion of contamination. Apart from the interrupter experiments, it is in general true that the most successful arrangements were the least satisfactory from the point of view of cleanliness. Additional support is lent to this view by a consideration of the status of the silver question. Silver was found and reported in many of the earlier experi­ ments, both of Miethe and of Nagaoka, but Miethe makes no mention of it in his later experiments, and has apparently ceased to estimate it. The whole question has been allowed to lapse until Haber in a recent paper called attention to its importance. It is almost inconceivable that the silver could be formed by disruption of the mercury atom, and if silver can find its way into the mercury by accidental contamination during the course of the experiments, there is nothing to exclude the possibility of the gold having a similar origin. It would thus seem to be a matter of the utmost importance to determine the silver simultaneously with the gold in every experiment in which gold is believed to be produced, as a direct check upon the thoroughness with which accidental contamination has been eliminated. It is unfortunate that Miethe has not continued to carry out this estimation in all his experiments. Haber has also reached the conclusion that Miethe’s gold came from his electrodes, and has given experimental evidence in support of his conclusions, though it must be admitted that this evidence is not altogether consistent with the results of the experiments described in this paper ; for, if contamina­ tion from the materials of the seals occurs as readily as Haber has found, it is difficult to understand the uniformly negative results of the present investiga­ tion. The writer feels that some of the results of Haber stand themselves in Reported Transmutation of Mercury into Gold. 405 need of further elucidation. In one experiment, in particular, he found an astonishing result. Here 97 per cent, of the entire gold content of several grams of nickel and steel wire, employed in the seals of a hot-filament discharge tube, diffused in some extraordinary way to the surface of the wire, whence it evaporated and found its way quantitatively to the mercury anticathode, from which it was recovered by analysis. This surprising observation, if confirmed, would be capable of explaining in a perfectly satisfactory manner most, if not all, of the discordant results obtained by the various experimenters. Haber, in a very recent paper (already quoted) has announced his intention of further investigating this phenomenon. In the meantime, an experiment hasbeen carried out by the writer in an attempt to explain it, but without success. Ordinary diffusion seems powerless to account for such a remarkable result, though it might possibly be brought about by some novel form of electrolysis.. To test this point, a small glass tube was divided into a number of air-tight compartments by shrinking the wall upon pieces of nickel-steel sealing-in wfires, which served to establish electrical connection between successive compart­ ments. Alternate cells were now filled with pure mercury and a 0*1 per cent, gold amalgam, each pure mercury compartment having amalgam on both sides of it, so as to catch gold electrolysing either way. A current of 2*5-3 amperes was passed in series through this tube and a similar one containing pure mercury throughout (to provide a blank in case of any positive result) for a number of hours. Tubes were analysed after runs of 250, 570 and 820 ampere hours respectively, and again it was proved by direct simultaneous determination that 10~8 gm. of gold could have been detected had it been present. No gold was found. Further results of Haber will be awaited with interest. Summary. The transmutation of mercury into gold, reported by Miethe and Stammreich, and by Nagaoka, has not been confirmed. The methods employed were as. follows :— A.—Condensed spark discharges at 15,000 volts were passed— 1. Between tungsten electrodes immersed in an emulsion of mercury droplets in transformer oil. 2. Between aluminium electrodes under the surface of distilled water carrying mercury in suspension. 3. Between an iron pole and a mercury surface in an atmosphere of hydrogen. 406 Reported Transmutation o f Mercury into Gold. B.—An interrupted direct-current arc of 30 amperes at 100 volts was run for .six days and nights between pure mercury poles in an atmosphere of hydrogen in a quartz tube, followed by a similar arc of 18 amperes at 240 volts for an equal period. Only 18*8 gm. of mercury were used, and the analysis was carried out without distillation, simultaneously with appropriate blank tests, which proved that 10~8 gm. of gold, had such a quantity been present, could not have escaped detection. No gold was found. Special stress is laid upon the last experiment, which duplicates the electrical conditions obtaining in the “ most reliable ” method of Miethe and Stammreich, while avoiding the attendant danger of contamination from foreign electrodes, and which should, in accordance with the results of these investigators, have yielded gold in quantities at least 104 times greater than the amount which could have been detected under the conditions of the experiment. Since the work of Miethe and Stammreich, in so far as it has dealt with analytical methods and with the distillation of mercury, has been in the main confirmed, the most probable inference is that the gold which they obtained was derived from the materials of their electrodes and their vessels. The same conclusion has been reached by Haber, but it is pointed out that some of the experiments which he has described to prove this point are themselves in need of further explanation. In conclusion, I wish to thank Prof. P. A. Lindemann for his kind and neverfailing interest throughout the work, and for numerous highly valuable sugges­ tions at every stage of its progress. The work described in this paper was carried out at the Clarendon Laboratory, Oxford, under his supervision. Acknowledgment is also due to the International Education Board, whose generous financial assistance rendered the work possible.