April 4, 1895J 



NATURE 



54.3 



planet's centre was 24" '4. Prof. Schaeberle now somewhat re- 

 luctantly publishes these facts in connection with his measures 

 of the known satellite, as he has not on any subsequent occasion 

 been able to detect any object in the neighbourhood of Neptune 

 in apparent orbital motion about the planet. The unusual 

 clearness and steadiness of the night of September 24, 1892, 

 however, is not considered to have been equalled in the later 

 observations. 



PROFESSOR MENDELEEFF ON ARGON. 



A T the meeting of the Russian Chemical Society, on March 

 •'*■ 14, Frof. MendelJeff made some interesting remarks on 

 the relations of argon to the periodic system. His views are 

 summed up as follows in a proof-issue of the Proceedings of the 

 Society : — 



" .-Vs regards argon we must consHer, first, whether it is a 

 chemical individual, or a mixture, and then, whether it is a 

 simple or a compound body. The supposition that it be a mix- 

 ture, lies beyond all probabilities ; it is contradicted by the re- 

 searches of Olszewski into the liquefaction and solidification of 

 argon. The supposition that it may be a compound has also 

 little in its favour. The remark .ible inactivity of argon testifies 

 in favour of its being a simple body, although there are, of 

 course, some compounds, al-o endowed with the same property 

 to some extent. The spectrum of argon, too, is characteristic 

 of a simple body. 



" Taking it as a simple body, we must then consider its pos- 

 sible atomic weight, the weight of its molecule being .lear to 40 

 {although, probably, a little over 40, because of a slight mix- 

 ture of nitrogen with llie argon). The atomic weight of argon 

 evidently dejiends upon the number of atoms which its molecule 

 contains. We must, therefore, consider the series of possible 

 molecular formulse : A, A.j, A3, . . . A„. 



" Upon the first supposition. A, the atomic weight of argon 

 would be about 40, and, like cadmium and mercury, it would 

 be a monatomic gas. 



" In favour of this supposition we have the specific heat 

 ratio at constant volumes and pressures, K, found by Rayleigh 

 and Ramsay to be near to r65, i.e. to the value which is con- 

 sidered as characteristic for monovalent gases. It must, how- 

 ever, be borne in mind that K varies for compound molecules, 

 even when these last contain the same numbers of atoms ; thus, 

 for most bivalent gases (nitrogen, oxygen, &c.) K is near to 

 I '4, while for chlorine it is I '3. This last figure makes one 

 think thai K depends not only upon the number of atoms in the 

 molecule, but also upon chemical energy, that is, upon the 

 stock of internal motion which determines the chemical activity 

 of a body, and the quantity of which must be relatively great 

 with chlorine. If, with the chemically-active chlorine, K is 

 notably less than i 4, we m.iy admit that for the inactive 

 argon it is much more than I '4, even though the molecule of 

 argon may contain two or more atoms. 



"If we admit that the molecule of argon contains but one 

 atom, there is no room for it in the periodic system ; because, 

 even if we suppose that its density is much below 20 (although 

 this is very unlikely to be the case, and the contrary could rather 

 be surmised), and that the atomic weight of argon should fall 

 between the atomic weights of chlorine and potassium, the new 

 body ought to be placed in the eighth group of the third series ; 

 but the existence of an eighth group in this series could hardly 

 be admitted. In fact, an eighth group is characteri^^ic of the 

 large periods ; and it establishes a link between the metallic 

 elements of the seventh groups of the even stries, with the 

 metallic elements akin to them, of the first groups of the uneven 

 series. It appears, therefore, very unlikely that the atomic 

 weight of argon might be about 40. 



" Upon the second supposition (A.j), its atomic weight would 

 be about 20, and in such a case argon would find its place in 

 the eighth group of the second series, i.e. after lluonne. Uut 

 the same objections as above could then be raised. Fluorine 

 and sodium are, moreover, strikingly unlike to each other. 

 However, it must be said in favour of this hypothesis that it 

 would have the advantages of analogy, by giving a new eighth 

 group to an even series. If we take also into consideration that 

 the typical series are possessed of several peculiarities, we may 

 be justified, to some extent, in supposing that the atomic weight 

 of argon is 20, this hypothesis being already much more 

 probable than the former (A = 40). 



NO. 1327. VOL. 51] 



" If we suppose, further, that the molecule of argon contains 

 three atoms, its atomic weight would be about 14, and in such 

 case we might consider argon as condensed nitrogen, Nj. 

 There is much to be said in favour of this last hypothesis. 

 First of all, the concurrent existence of nitrogen and argon in 

 nature ; then, the fact that many of the bright lines of the two 

 spectra are very near to each other. Then, again, the in- 

 activity of argon would be easily explained, if it originates from 

 nitrogen, N„, with giving up heat. And finally, the fact of its 

 having been obtained, though in a relatively small quantity, 

 from artificially obtained nitrogen. The supposition of Rayleigh 

 and Ramsay, according to which argon has been disengaged in 

 this last case from water, is very probable, but at any rate it is 

 not yet proved. The hypothesis of argon being condensed 

 nitrogen might be tested by means of introducing boron, or 

 titanium, into an atmosphere of argon, strongly heated, and 

 through which electric sparks would be passed. 



"If we suppose, next, that the molecule of argon contains 

 four or five atoms, its atomic weight will be 10, or 8, and in 

 such case there is no room for argon in the periodic system. 



" And finally, if we admit that its molecule contains six 

 atoms, and that its atomic weight is 65, we must place it in 

 the first series. In such case, it would probably take its place 

 in the fifth group. Accordingly, the suppositions that argon is 

 condensed nitrogen, N^, or that, containing six atoms in the 

 molecule, its place is in the first series of the system, appear to 

 be the more probable ones, if it is a pure simple chemical body. 



"Fiom a letter received by D. I. Mendeleeff from Prof. 

 Ramsay, it appears that the investigation of argon is being 

 continued, and that the body finds its place in the periodic 

 system ; but the ultimate results of the researches of the two 

 authors, who have brought before chemistry such an important 

 new problem, and given it such an exemplary investigi'.ion, ari 

 not yet known." 



TERRESTRIAL HELIUM {^). 



W 



E referred last week to Prof. Ramsay's discovery of another 

 new gas obtained from cleveite. The following papers, 

 by Prof. Ramsay and Mr. Crookes, on this subject were com- 

 municated to the Chemical Society at its anniversary meeting. 



Prof. Ramsay's paper was as follows : — 



In seeking a clue to compounds of argon, I was led to repeat 

 experiments of Hillebrand on cleveite, which, as is known, 

 when boiled with weak sulphuric acid, gives off a gas hitherto 

 supposed to be nitrogen. This gas proved to be almost free 

 from nitrogen ; its spectrum in a Ptliicker's tube showed all the 

 prominent argon lines, and, in addition, a brilliant line close 

 to, but ;iot coinciding with, the D lines of sodium. There are, 

 moreover, a number of other lines, of which one in the green- 

 blue is especially prominent. Atmospheric argon shows, be- 

 sides, three lines in the violet which are not to be seen, o--, if 

 present, are excessively feeble, in the spectrum of the gas from 

 cleveite. This suggests that atmospheric argon contains, be 

 sides argon, some other gas which has as yet not been separated, 

 and which may possibly account for the anomalous position of 

 argon in its numerical relations with other elements. 



Not having a spectroscope with which accurate measure- 

 ments can be made, I sent a tube of the gas to Mr. Crookes, 

 who has identified the yellow line with that of the solar element 

 to which the name " Helium" has been given. He ha; kindly 

 undertaken to make an exhaustive study of its spectrum. 



I have obtained a considerable quantity of this mixture, and 

 hope soon to be able to report concerning its properties. A 

 determination of its density promises to be of great interest. 



The spectrum of the gas was next discussed by Mr. Crookes, 

 V, ho said 



By the kindness of Prof. Ramsay I have been enabled to 

 examine spectroscopically two P.'lucker tubes filled with some of 

 the gas obtained from the rare mineral cleveite.' The nitrogen 

 had been removed by " sparking." On looking at the spectrum, 

 by far the most prominent line was seen to be a brilliant yellow 

 one apparently occupying the position of the sodium lines. 



1 Clcvcile is a variety of uraninite, chiefly a tiranate of uranvlc, lead, 

 and the rare carlhi. It conrains abouti^ per cent, of the rare eartht. and 

 at>out 3's per cent, of a gas said to be nitrogen. 



