When an electrical discharge is passed through a high-vacuum tube, invisible rays are emitted from the kathode, generally with the production of a greenish-yellow fluorescence where they strike the glass walls of the tube. These rays are called “kathode rays.” At one time they were regarded as waves in the ether, but it was shown by Sir William Crookes that they consist of small electrically charged particles, moving with a very high velocity. Sir J. J. Thomson was able to determine the ratio of the charge carried by these particles to their mass or inertia; he found that this ratio was constant whatever gas was contained in the vacuum tube, and much greater than the corresponding ratio for the hydrogen ion (electrically charged hydrogen atom) in electrolysis. By a skilful method, based on the fact discovered by Mr. C. T. R. Wilson, that charged particles can serve as nuclei for the condensation of water-vapour, he was further able to determine the value of the electrical charge carried by these particles, which was found to be constant also, and equal to the charge carried by univalent ions, e.g., hydrogen, in electrolysis. Hence, it follows that the mass of these kathode particles must be much smaller than the hydrogen ion, the actual ratio being about 1 : 1700. The first theory put forward by Sir J. J. Thomson in explanation of these facts, was that these kathode particles (“corpuscles” as he termed them) were electrically charged portions of matter, much smaller than the smallest atom; and since the same sort of corpuscle is obtained whatever gas is contained in the vacuum tube, it is reasonable to conclude that the corpuscle is the common unit of all matter.

Proof that the Electrons are not Matter.

§ 80. This eminent physicist, however, had shown mathematically that a charged particle moving with a very high velocity (approaching that of light) would exhibit an appreciable increase in mass or inertia due to the charge, the magnitude of such inertia depending on the velocity of the particle. This was experimentally verified by Kaufmann, who determined the velocities, and the ratios between the electrical charge and the inertia, of various kathode particles and similar particles which are emitted by compounds of radium (see §§ 89 and 90). Sir J. J. Thomson calculated these values on the assumption that the inertia of such particles is entirely of electrical origin, and thereby obtained values in remarkable agreement with the experimental. There is, therefore, no reason for supposing the corpuscle to be matter at all; indeed, if it were, the above agreement would not be obtained. As Professor Jones says: “Since we know things only by their properties, and since all the properties of the corpuscle are accounted for by the electrical charge associated with it, why assume that the corpuscle contains anything but the electrical charge? It is obvious that there is no reason for doing so.

“The corpuscle is, then, nothing but a disembodied electrical charge, containing nothing material, as we have been accustomed to use that term. It is electricity, and nothing but electricity. With this new conception a new term was introduced, and, now, instead of speaking of the corpuscle we speak of the electron.”[96] Applying this modification to the above view of the constitution of matter, we have what is called “the electronic theory,” namely, that the material atoms consist of electrons, or units of electricity in rapid motion; which amounts to this—that matter is simply an electrical phenomenon.

The Electronic Theory of Matter.

§ 81. Sir J. J. Thomson has elaborated this theory of the nature and constitution of matter; he has shown what systems of electrons would be stable, and has attempted to find therein the significance of Mendeléeff’s generalisation and the explanation of valency. There can be no doubt that there is a considerable element of truth in the electronic theory of matter; the one characteristic property of matter, i.e., inertia, can be accounted for electrically. The fundamental difficulty is that the electrons are units of negative electricity, whereas matter is electrically neutral. Several theories have been put forward to surmount this difficulty. Certainly the electron is a constituent of matter; but is it the sole constituent? Recent research indicates that, as already pointed out, all atoms consist of two distinct portions, a massive central nucleus, whose net charge is positive, surrounded by a number of electrons, just sufficient to neutralize this charge. The point of greatest interest is that the indicated number of free electrons is exactly the number which expresses the position of the element in the Periodic Table, reckoning helium as 2, lithium as 3, and so on; and it would seem that the chemical properties of the elements are determined entirely by these electrons, and are, therefore, not, strictly speaking, periodic functions of their atomic weights, as was formerly thought (§ 78), but of their atomic numbers. The exact nature of the nuclei of the various atoms has yet to be determined: in the case of the atoms heavier than helium they would appear to be made up of the nuclei of hydrogen and (or) helium atoms together with—in many cases—electrons insufficient in number to neutralize the positive charges associated with these.

The Etheric Theory of Matter.

§ 82. The analysis of matter has been carried a step further. A philosophical view of the Cosmos involves the assumption of an absolutely continuous and homogeneous medium filling all space, for an absolute vacuum is unthinkable, and if it were supposed that the stuff filling all space is of an atomic structure, the question arises, What occupies the interstices between its atoms? This ubiquitous medium is termed by the scientists of to-day “the Ether of Space.” Moreover, such a medium as the Ether is demanded by the phenomena of light. It appears, however, that the ether of space has another and a still more important function than the transmission of light: the idea that matter has its explanation therein has been developed by Sir Oliver Lodge. The evidence certainly points to the conclusion that matter is some sort of singularity in the ether, probably a stress centre. We have been too much accustomed to think of the ether as something excessively light and quite the reverse of massive or dense, in which it appears we have been wrong. Sir Oliver Lodge calculates that the density of the ether is far greater than that of the most dense forms of matter; not that matter is to be thought of as a rarefaction of the ether, for the ether within matter is as dense as that without. What we call matter, however, is not a continuous substance; it consists, rather, of a number of widely separated particles, whence its comparatively small density compared with the perfectly continuous ether. Further, if there is a difficulty in conceiving how a perfect fluid like the ether can give rise to a solid body possessed of such properties as rigidity, impenetrability and elasticity, we must remember that all these properties can be produced by means of motion. A jet of water moving with a sufficient velocity behaves like a rigid and impenetrable solid, whilst a revolving disc of paper exhibits elasticity and can act as a circular saw.[97] It appears, therefore, that the ancient doctrine of the alchemistic essence is fundamentally true after all, that out of the “One Thing” all material things have been produced by adaptation or modification; and, as we have already noticed (§ 60), there also appears to be some resemblance between the concept of the electron and that of the seed of gold, which seed, it should be borne in mind, was regarded by the alchemists as the common seed of all metals.

Further Evidence of the Complexity of the Atoms.

§ 83. There are also certain other facts which appear to demand such a modification of Dalton’s Atomic Theory as is found in the Electronic Theory. One of the characteristics of the chemical elements is that each one gives a spectrum peculiar to itself. The spectrum of an element must, therefore, be due to its atoms, which in some way are able, at a sufficiently high temperature, to act upon the ether so as to produce vibrations of definite and characteristic wave-length. Now, in many cases the number of lines of definite wave-length observed in such a spectrum is considerable, for example, hundreds of different lines have been observed in the arc-spectrum of iron. But it is incredible that an atom, if it were a simple unit, would give rise to such a number of different and definite vibrations, and the only reasonable conclusion is that the atoms must be complex in structure. We may here mention that spectroscopic examination of various heavenly bodies leads to the conclusion that there is some process of evolution at work building up complex elements from simpler ones, since the hottest nebulæ appear to consist of but a few simple elements, whilst cooler bodies exhibit a greater complexity.

Views of Wald and Ostwald.

§ 84. Such modifications of the atomic theory as those we have briefly discussed above, although profoundly modifying, and, indeed, controverting the philosophical significance of Dalton’s theory as originally formulated, leave its chemical significance practically unchanged. The atoms can be regarded no longer as the eternal, indissoluble gods of Nature that they were once supposed to be; thus, Materialism is deprived of what was thought to be its scientific basis.[98] But the science of Chemistry is unaffected thereby; the atoms are not the ultimate units out of which material things are built, but the atoms cannot be decomposed by purely chemical means; the “elements” are not truly elemental, but they are chemical elements. However, the atomic theory has been subjected to a far more searching criticism. Wald argues that substances obey the law of definite proportions because of the way in which they are prepared; chemists refuse, he says, to admit any substance as a definite chemical compound unless it does obey this law. Wald’s opinions have been supported by Professor Ostwald, who has attempted to deduce the other stoichiometric laws on these grounds without assuming any atomic hypothesis[99]; but these new ideas do not appear to have gained the approval of chemists in general. It is not to be supposed that chemists will give up without a struggle a mental tool of such great utility as Dalton’s theory, in spite of its defects, has proved itself to be. There does seem, however, to be logic in the arguments of Wald and Ostwald, but the trend of recent scientific theory and research does not appear to be in the direction of Wald’s views. Certainly, however, it appears that, on the one hand, the atomic theory is not necessitated by the so-called “stoichiometric laws”; but, on the other hand, a molecular constitution of matter seems to be demanded by the phenomenon known as the “Brownian Movement,” i.e., the spontaneous, irregular and apparently perpetual movement of microscopic portions of solid matter when immersed in a liquid medium; such movement appearing to be explicable only as the result of the motion of the molecules of which the liquid in question is built up.[100]

CHAPTER VII
MODERN ALCHEMY

“Modern Alchemy.”

§ 85. Correctly speaking, there is no such thing as “Modern Alchemy”; not that Mysticism is dead, or that men no longer seek to apply the principles of Mysticism to phenomena on the physical plane, but they do so after another manner from that of the alchemists. A new science, however, is born amongst us, closely related on the one hand to Chemistry, on the other to Physics, but dealing with changes more profound and reactions more deeply seated than are dealt with by either of these; a science as yet without a name, unless it be the not altogether satisfactory one of “Radioactivity.” It is this science, or, perhaps we should say, a certain aspect of it, to which we refer (it may be fantastically) by the expression “Modern Alchemy”: the aptness of the title we hope to make plain in the course of the present chapter.

§ 86. As is commonly known, what are called X-rays are produced when an electric discharge is passed through a high-vacuum tube. It has been shown that these rays are a series of irregular pulses in the ether, which are set up when the kathode particles strike the walls of the glass vacuum tube,[101] and it was found that more powerful effects can be produced by inserting a disc of platinum in the path of the kathode particles. It was M. Becquerel who first discovered that there are substances which naturally emit radiations similar to X-rays. He found that uranium compounds affected a photographic plate from which they were carefully screened, and he also showed that these uranium radiations, or “Becquerel rays,” resemble X-rays in other particulars. It was already known that certain substances fluoresce (emit light) in the dark after having been exposed to sunlight, and it was thought at first that the above phenomenon exhibited by uranium salts was of a like nature, since certain uranium salts are fluorescent; but M. Becquerel found that uranium salts which had never been exposed to sunlight were still capable of affecting a photographic plate, and that this remarkable property was possessed by all uranium salts, whether fluorescent or not. This phenomenon is known as “radioactivity,” and bodies which exhibit it are said to be “radioactive.” Schmidt found that thorium compounds possess a similar property, and Professor Rutherford showed that thorium compounds evolved also something resembling a gas. He called this an “emanation.”

The Discovery of Radium.

§ 87. Mme. Curie[102] determined the radioactivity of many uranium and thorium compounds, and found that there was a proportion between the radioactivity of such compounds and the quantity of uranium or thorium in them, with the remarkable exception of certain natural ores, which had a radioactivity much in excess of the normal, and, indeed, in certain cases, much greater than pure uranium. In order to throw some light on this matter, Mme. Curie prepared one of these ores by a chemical process and found that it possessed a normal radioactivity. The only logical conclusion to be drawn from these facts was that the ores in question must contain some unknown, highly radioactive substance, and the Curies were able, after very considerable labour, to extract from pitchblende (the ore with the greatest radioactivity) minute quantities of the salts of two new elements—which they named “Polonium” and “Radium” respectively—both of which were extremely radioactive.

M. Debierne has obtained a third radioactive substance from pitchblende, which he has called “Actinium.”

Chemical Properties of Radium.

§ 88. Radium is an element resembling calcium, strontium, and barium in chemical properties; its atomic weight was determined by Mme. Curie, and found to be about 225, according to her first experiments; a redetermination gave a slightly higher value, which has been confirmed by a further investigation carried out by Sir T. E. Thorpe.[103] Radium gives a characteristic spectrum, and is intensely radioactive. It should be noted that up to the middle of the year 1910 the element radium itself had not been prepared; in all the experiments carried out radium salts were employed (i.e., certain compounds of radium with other elements), generally radium chloride and radium bromide. In that year, however, Mme. Curie, in conjunction with M. Debierne, obtained the free metal. It is described as a white, shining metal resembling the other alkaline earth metals. It reacts very violently with water, chars paper with which it is allowed to come in contact, and blackens in the air, probably owing to the formation of a nitride. It fuses at 700° C., and is more volatile than barium.[104]

The Radioactivity of Radium.

§ 89. Radium salts give off three distinct sorts of rays, referred to by the Greek letters α, β, γ. The α-rays have been shown to consist of electrically charged (positive) particles, with a mass approximately equal to that of four hydrogen atoms; they are slightly deviated by a magnetic field, and do not possess great penetrative power. The β-rays are similar to the kathode rays, and consist of (negative) electrons; they are strongly deviated by a magnetic field, in a direction opposite to that in which the α-particles are deviated, and possess medium penetrative power, passing for the most part through a thin sheet of metal. The γ-rays resemble X-rays; they possess great penetrative power, and are not deviated by a magnetic field. The difference in the effect of the magnetic field on these rays, and the difference in their penetrative power, led to their detection and allows of their separate examination. Radium salts emit also an emanation, which tends to become occluded in the solid salt, but can be conveniently liberated by dissolving the salt in water, or by heating it. The emanation exhibits the characteristic properties of a gas, it obeys Boyle’s Law (i.e., its volume varies inversely with its pressure), and it can be condensed to a liquid at low temperatures; its density as determined by the diffusion method is about 100. Attempts to prepare chemical compounds of the emanation have failed, and in this respect it resembles the rare gases of the atmosphere—helium, neon, argon, krypton, and xenon—whence it is probable that its molecules are monatomic, so that a density of 100 would give its atomic weight as 200.[105] As can be seen from the table on pp. 106, 107, an atomic weight of about 220 corresponds to a position in the column containing the rare gases in the periodic system. That the emanation actually has an atomic weight of these dimensions was confirmed by further experiments carried out by the late Sir William Ramsay and Dr. R. W. Gray.[106] These chemists determined the density of the emanation by actually weighing minute quantities of known volume of the substance, sealed up in small capillary tubes, a specially sensitive balance being employed. Values for the density varying from 108 to 113¹⁄₂, corresponding to values for the atomic weight varying from 216 to 227, were thereby obtained. Sir William Ramsay, therefore, considered that there could no longer be any doubt that the emanation was one of the elements of the group of chemically inert gases. He proposed to call it Niton, and, for reasons which we shall note later, considered that in all probability it had an atomic weight of about 222¹⁄₂.

The Disintegration of the Radium Atom.

§ 90. Radium salts possess another very remarkable property, namely, that of continuously emitting light and heat. It seemed, at first, that here was a startling contradiction to the law of the conservation of energy, but the whole mystery becomes comparatively clear in terms of the corpuscular or the electronic theory of matter. The radium-atom is a system of a large number (see § 81) of corpuscles or electrons, and contains in virtue of their motion an enormous amount of energy. But it is known from Chemistry that atomic systems (i.e., molecules) which contain very much energy are unstable and liable to explode. The same law holds good on the more interior plane—the radium-atom is liable to, and actually does, explode. And the result? Energy is set free, and manifests itself partly as heat and light. Some free electrons are shot off (the β-rays), which, striking the undecomposed particles of salt, give rise to pulses in the ether (the γ-rays),[107] just as the kathode particles give rise to X-rays when they strike the walls of the vacuum tube or a platinum disc placed in their path. The β- and γ-rays do not, however, result immediately from the exploding radium-atoms, the initial products being the emanation and one α-particle from each radium-atom destroyed.

“Induced Radioactivity.”

§ 91. Radium salts have the property of causing surrounding objects to become temporally radioactive. This “induced radioactivity,” as it may be called, is found to be due to the emanation, which is itself radioactive (it emits α-rays only), and is decomposed into minute traces of solid radioactive deposits. By examining the rate of decay of the activity of the deposit, it has been found that it is undergoing a series of sub-atomic changes, the products being termed Radium A, B, C, &c. It has been proved that all the β- and γ-rays emitted by radium salts are really due to certain of these secondary products. Radium F is thought to be identical with Polonium (§ 87). Another product is also obtained by these decompositions, with which we shall deal later (§ 94).

Properties of Uranium and Thorium.

§ 92. Uranium and thorium differ in one important respect from radium, inasmuch as the first product of the decomposition of the uranium and thorium atoms is in both cases solid. Sir William Crookes[108] was able to separate from uranium salts by chemical means a small quantity of an intensely radioactive substance, which he called Uranium X, the residual uranium having lost most of its activity; and M. Becquerel, on repeating the experiment, found that the activity of the residual uranium was slowly regained, whilst that of the uranium X decayed. This is most simply explained by the theory that uranium first changes into uranium X. It has been suggested that radium may be the final product of the breaking up of the uranium-atom; at any rate, it is quite certain that radium must be evolved in some way, as otherwise there would be none in existence—it would all have decomposed. This suggestion has been experimentally confirmed, the growth of radium in large quantities of a solution of purified uranyl nitrate having been observed. Uranium gives no emanation. Thorium probably gives at least three solid products—Meso-thorium, Radio-thorium, and Thorium X, the last of which yields an emanation resembling that obtained from radium, but not identical with it.

The Radium Emanation.

§ 93. We must now more fully consider the radium emanation—a substance with more astounding properties than even the radium compounds themselves. By distilling off the emanation from some radium bromide, and measuring the quantities of heat given off by the emanation and the radium salt respectively, Professors Rutherford and Barnes[109] proved that nearly three-fourths of the total amount of heat given out by a radium salt comes from the minute quantity of emanation that it contains. The amount of energy liberated as heat during the decay of the emanation is enormous; one cubic centimetre liberates about four million times as much heat as is obtained by the combustion of an equal volume of hydrogen. Undoubtedly this must indicate some profound change, and one may well ask, What is the ultimate product of the decomposition of the emanation?

The Production of Helium from Radium.

§ 94. It had been observed already that the radioactive minerals on heating give off Helium—a gaseous element, characterised by a particular yellow line in its spectrum—and it seemed not unlikely that helium might be the ultimate decomposition product of the emanation. A research to settle this point was undertaken by Sir William Ramsay and Mr. Soddy,[110] and a preliminary experiment having confirmed the above speculation, they carried out further very careful experiments. “The maximum amount of the emanation obtained from 50 milligrams of radium bromide was conveyed by means of oxygen into a U-tube cooled in liquid air, and the latter was then extracted by the pump.” The spectrum was observed; it “was apparently a new one, probably that of the emanation itself. . . . After standing from July 17 to 21 the helium spectrum appeared, and the characteristic lines were observed.” Sir William Ramsay performed a further experiment with a similar result, in which the radium salt had been first of all heated in a vacuum for some time, proving that the helium obtained could not have been occluded in it; though the fact that the helium spectrum did not immediately appear, in itself proves this point. Sir William Ramsay’s results were confirmed by further careful experiments by Sir James Dewar and other chemists. It was suggested, therefore, that the α-particle consists of an electrically charged helium-atom, and not only is this view in agreement with the value of the mass of this particle as determined experimentally, but it has been completely demonstrated by Professor Rutherford and Mr. Royds. These chemists performed an experiment in which the emanation from about one-seventh of a gramme of radium was enclosed in a thin-walled tube, through the walls of which the α-particles could pass, but which were impervious to gases. This tube was surrounded by an outer jacket, which was evacuated. After a time the presence of helium in the space between the inner tube and the outer jacket was observed spectroscopically.[111] Now, the emanation-atom results from the radium-atom by the expulsion of one α-particle; and since this latter consists of an electrically charged helium-atom, it follows that the emanation must have an atomic weight of 226 - 4, i.e., 222. This value is in agreement with Sir William Ramsay’s determination of the density of the emanation. We may represent the degradation of the radium-atom, therefore, by the following scheme:—

Nature of this Change.

§ 95. Here, then, for the first time in the history of Chemistry, we have the undoubted formation of one chemical element from another, for, leaving out of the question the nature of the emanation, there can be no doubt that radium is a chemical element. This is a point which must be insisted upon, for it has been suggested that radium may be a compound of helium with some unknown element; or, perhaps, a compound of helium with lead, since it has been shown that lead is probably one of the end products of the decomposition of radium. The following considerations, however, show this view to be altogether untenable: (i.) All attempts to prepare compounds of helium with other elements have failed. (ii.) Radium possesses all the properties of a chemical element; it has a characteristic spectrum, and falls in that column in the Periodic Table with those elements which it resembles as to its chemical properties. (iii.) The quantity of heat liberated on the decomposition of the emanation is, as we have already indicated, out of all proportion to that obtained even in the most violent chemical reactions; and (iv.) one very important fact has been observed, namely, that the rate of decay of the emanation is unaffected by even extreme changes of temperature, whereas chemical actions are always affected in rate by changes of temperature. It will also be advisable, perhaps, to indicate some of the differences between helium and the emanation. The latter is a heavy gas, condensable to a liquid by liquid air (recently it has been solidified[112]); whereas helium is the lightest of all known gases with the exception of hydrogen and has been liquefied only by the most persistent effort.[113] The emanation, moreover, is radioactive, giving off α-particles, whereas helium does not possess this property.

Is this Change a true Transmutation?

§ 96. It has been pointed out, however, that (in a sense) this change (viz., of emanation into helium) is not quite what has been meant by the expression “transmutation of the elements”; for the reason that it is a spontaneous change; no effort of ours can bring it about or cause it to cease.[114] But the fact of the change does go to prove that the chemical elements are not the discrete units of matter that they were supposed to be. And since it appears that all matter is radioactive, although (save in these exceptional cases) in a very slight degree,[115] we here have evidence of a process of evolution at work among the chemical elements. The chemical elements are not permanent; they are all undergoing change; and the common elements merely mark those points where the rate of the evolutionary process is at its slowest. (See also §§ 78 and 83.) Thus, the essential truth in the old alchemistic doctrine of the growth of metals is vindicated, for the metals do grow in the womb of Nature, although the process may be far slower than appears to have been imagined by certain of the alchemists,[116] and although gold may not be the end product. As writes Professor Sir W. Tilden: “. . . It appears that modern ideas as to the genesis of the elements, and hence of all matter, stand in strong contrast with those which chiefly prevailed among experimental philosophers from the time of Newton, and seem to reflect in an altered form the speculative views of the ancients.” “. . . It seems probable,” he adds, “that the chemical elements, and hence all material substances of which the earth, the sea, the air, and the host of heavenly bodies are all composed, resulted from a change, corresponding to condensation, in something of which we have no direct and intimate knowledge. Some have imagined this primal essence of all things to be identical with the ether of space. As yet we know nothing with certainty, but it is thought that by means of the spectroscope some stages of the operation may be seen in progress in the nebulæ and stars. . . .”[117] We have next to consider whether there is any experimental evidence showing it to be possible (using the phraseology of the alchemists) for man to assist in Nature’s work.

The Production of Neon from Emanation.

§ 97. As we have already indicated above (§ 93), the radium emanation contains a vast store of potential energy, and it was with the idea of utilising this energy for bringing about chemical changes that Sir William Ramsay[118] undertook a research on the chemical action of this substance—a research with the most surprising and the most interesting results, for the energy contained within the radium emanation appeared to behave like a veritable Philosopher’s Stone. The first experiments were carried out on distilled water. It had already been observed that the emanation decomposes water into its gaseous elements, oxygen and hydrogen, and that the latter is always produced in excess. These results were confirmed and the presence of hydrogen peroxide was detected, explaining the formation of an excess of hydrogen; it was also shown that the emanation brings about the reverse change to some extent, causing oxygen and hydrogen to unite with the production of water, until a position of equilibrium is attained. On examining spectroscopically the gas obtained by the action of the emanation on water, after the removal of the ordinary gases, a most surprising result was observed—the gas showed a brilliant spectrum of neon, accompanied with some faint helium lines. A more careful experiment was carried out later by Sir William Ramsay and Mr. Cameron, in which a silica bulb was employed instead of glass. The spectrum of the residual gas after removing ordinary gases was successfully photographed, and a large number of the neon lines identified; helium was also present. The presence of neon could not be explained, in Ramsay’s opinion, by leakage of air into the apparatus, as the percentage of neon in the air is not sufficiently high, whereas this suggestion might be put forward in the case of argon. Moreover, the neon could not have come from the aluminium of the electrodes (in which it might be thought to have been occluded), as the sparking tube had been used and tested before the experiment was carried out. The authors conclude: “We must regard the transformation of emanation into neon, in presence of water, as indisputably proved, and, if a transmutation be defined as a transformation brought about at will, by change of conditions, then this is the first case of transmutation of which conclusive evidence is put forward.”[119] However, Professor Rutherford and Mr. Royds have been unable to confirm this result. They describe[120] attempts to obtain neon by the action of emanation on water. Out of five experiments no neon was obtained, save in one case in which a small air leak was discovered; and, since the authors find that very minute quantities of this gas are sufficient to give a clearly visible spectrum, they conclude that Ramsay’s positive results are due, after all, to leakage of air into the apparatus. But if this is the true explanation of Ramsay’s results, it is difficult to understand why, in the case of the experiment with a solution of a copper salt described below, the presence of neon was not detected, for, if due to leakage, the proportions of the rare gases present should presumably have been the same in all the experiments. Further research seems necessary conclusively to settle the question.