THE discovery of krypton and neon was announced to the Royal Society in the early summer of 1898; and subsequently atmospheric air was found to contain a heavier gas to which the name of xenon was applied. Mr. Baly, in the autumn of the same year, called attention to the presence of helium lines in the spectrum of neon, an observation which confirms that made by Prof. Kayser, of Bonn, and by Dr. Friedlander, of Berlin. At the same time we imagined that we had obtained a gas with a spectrum differing from that of argon and yet of approximately the same density; to this gas we gave the name metargon. It has now been found that the presence of the so-called metargon is to be accounted for by the fact that in removing oxygen from the mixture of. these gases, which was then in our hands, phosphorus containing carbon was employed; this mixture when burned in oxygen yields a spectrum to some extent identical with that furnished by carbon monoxide, but differing from” it inasmuch as lines of cyanogen are also present. We have no doubt that the so-called metargon, the spectrum of which is visible only at high pressure, and only when impure phosphorus has been employed to remove oxygen, must be attributed to some carbon compound. In spite of numerous experiments we have not yet succeeded ' in producing any gas in quantity which yields this composite spectrum. It is only to be obtained by a mixture of carbon monoxide with cyanogen. To obtain the heavier gases krypton and xenon, a large amount of air was allowed to evaporate quietly; the residue was freed from oxygen and nitrogen, and then consisted of a mixture of krypton, xenon, and argon, the last forming by far the largest portion of the gas; this mixture was liquefied by causing it to flow into a bulb immersed in liquid air, and the bulk of the argon was removed as soon as the temperature rose, the krypton and the xenon being left behind. By many repetitions of this process we were finally successful in separating these three gases from each other. While krypton has a considerable vapor-pressure at the temperature of boiling air, the vapor-ptessure of xenon is hardly appreciable, and this afforded a means of finally separating these two gases from one another; in the complete paper the operations necessary to separate them are fully described. For neon the process of preparation was different. The air liquefier furnished a supply of liquid air; the gas escaping from the liquefier consisted largely of nitrogen; this mixture was liquefied in a bulb immersed in the liquid air which the machine was making. When the bulb had been filled with liquid nitrogen a current of air was blown through the liquid until some of the gas had evaporated. That gas was collected separately, and deprived of oxygen by passage over red-hot copper; it contained the main portion of the neon and the helium present in the air. The remainder of the nitrogen was added to the liquid air used for cooling the bulb in which the nitrogen was condensed. Having obtained a considerable quantity of this light nitrogen it was purified from that gas in the usual man * A paper by Prof. William Ramsay. F.R.S.. and Dr. Morris W. Travers. Itead at the Royal Society on November 15,1900. Abstract in Nature. ner, and the argon containing helium and neon was liquefied. By fractional distillation it was possible to remove the greater portion of the helium and neon from this mixture of gases, leaving 'the argon behind. Many attempts were made to separate the helium from the neon. Among these was fractional solution in oxygen, followed by a systematic diffusion of the two gases; but it was not found possible to raise the density of the neon beyond the number 9.16, and its spectrum still showed helium lines. It was not until liquid hydrogen, made by an apparatus designed and built by oil” of us (M. W. T.), had been produced in quantity, that the separation was effected; the neon was liquefied or perhaps solidified at a temperature of boning hydrogen, while the helium remained gaseous. few frac- tionations serve to produce pure neon; we did not attempt to separate the helium in a pure state from this mixture. That these are all monatomic gases was proved by determinaWon of the ratio of their specific heats by Kundt's method; the physical properties which we have determined are the refractivities, the densities and the compressibilities at two temperatures, and of argon, krypton, and xenon the vapor-pressures and the volumes of the liquids at their boiling points. The results are as follows: Helium. Neon. Argort. Krypton. Xenon. Refractivi ties (Air = I)... 0'i238 0'2345 O'968 1 '449 2'364 Densities of Gases (0 =I6) I'98 9 '97 I9'96 4°'88 64 Boiling-points 86'9° at 760 mm. ? ? 121 '33° i63'90- abs. abs. abs. Critical tem 287'7° peratures... ? below 68° i55'6° 210'5° abs. abs. abs. abs. Critical pres sures ? ? 40'2 41'24 43'5 metres metres metres Vapour-pres- 0'O675 sure ratio... ? ? 0-0350 0'0467 Weight of I c. c. of liquid ? ? 1'212 2'I55 3'52 grammes grammes grammes Molecular vol 36-40 umes ? ? 32-92 37'84 The compressibilities of these gases also show interesting features. They were measured at two temperatures—11.2 degrees and 237.3 degrees; the value of P.V. for an ideal and perfect gas at 11.2 degrees is 17,710 meter-cubic-centimeters, and at 237.3 degrees to 31,800. This is, of course, on the assumption that the product remains constant whatever be the variation in pressure. Now with hydrogen at 11.2 deg. C. the product increases with the rise of pressure; with nitrogen, according to Amagat, it first decreases slightly and then increases slightly. With helium the increase is more rapid than with hydrogen; with argon there is first a considerable decrease followed at very high pressures by a gentle increase, although the product doEts-not reach the theoretical value at 100 atmospheres pressure; with krypton the change with rise of pressure is a still more marked decrease, and with xenon the decrease is very sudden. At the higher temperature the results are more difficult to interpret; while nitrogen maintains its nearly constant value for P.V., helium decreases rapidly, then increases, and the same peculiarity is to be remarked with the other gases, although they do not give the product of P.V. coinciding with that calculable by assuming that the increase of P.V. is proportional to the rise of absolute temperature. Tb, ese last experiments must be taken as merely preliminary; but they show that further research in this direction would be productive of interesting results. The spectra of these gases have been accurately measured by Mr. E. C. C. Baly, with a Rowland's grating; the results of his measurements will shortly be published. It may be remarked, however, that the color of a neon-tube is extremely brilliant and of an orange-pink hue; it resembles nothing so much as a flame; and it is characterized by a multitude of intense orange and yellow lines; that' of krypton is pale violet; and that of xenon is sky-blue. The paper contains plates showing the most brilliant lines of the visible spectrum. That the gases form a series in the periodic table, between that of fluorine and that of sodium, is proved by three lines of argument: The ratio betwen their specific heats at constant pressure and constant volume is 1.66. If the densities be regarded as identical with the atomic weights, as in the case with diatomic gases such as hydrogen, oxygen, and nitrogen, there is no place for these elements in the periodic table. The group of elements which includes them is: Hydrogen, Helium. Lithium. Beryllium. I 4 7 9 Fluorine. Neon. Sodium. Magnesium. 18 20 23 24 Chlorine, Argon. Potassium. Calcium. 35'5 40 39 40 Bromine. Krypton. Rubidium. Strontium. 80 82 85 87 Iodine. Xenon. Cresium. Barium. 127 128 133 131 (For arguments in favor of placing hydrogen at the head of the fluorine group of elements, see Orme Masson, Chern. News, vol. lxxiii., 1896, page 283.) (3) These elements exhibit gradations in properties such as refractive index, atomic volume, melting-point and boiling-point, which find a fitting place on diagrams showing such periodic relations. Some of these diagrams are reproduced in the original paper. Thus the refractive equivalents are found at the lower apices of the descending curves; the atomic volumes, on the ascending branches, in appropriate positions; and the melting and boiling-points, like the refractivities, occupy positions at the lower apices. Although, however, such regularity is to be notiaed, similar to that which is found with other elements, we had entertained hopes that the simple nature of the molecules of the inactive gases might have thrown light on the “puzzling incongruities of the periodic table. That hope has been disappointed. We have not been able to predict accurately any one of the properties of one of these gases from a knowledge of those of the others; an approximate guess is all that can be made. The conundrum of the periodic table has yet to be solved