oj4 



NA JURE 



[August i, 1895 



between their specific heats at constant volume and at constant 

 pressure, both are monatomic gases. These properties un- 

 doubtedly place them in the same chemical class, and differentiate 

 them from all known elements. 



.Although opinion is diWded on the precise significance of the 

 ratio of s()ecihc heats, I '66, it ap|)ears to be most probable that 

 in all cases, as in that of niercur)-, this ratio jwints to the 

 monatomicity of the molecule. I( we assume this provisionally, 

 it follows that the atomic weight of helium is identical w ith its 

 molecular weight. The molecular weight is twice the density, 

 for the molecular w eights of gases are coni|xired w ith the atomic 

 weight of hydrogen, taken as unity ; hence the atomic 

 weight of helium on this assumption is 2'l3x2 = 4"26. But 

 agam we assume, in making this calculation, that helium is a 

 single element, and not a mixture of elements. Before dis- 

 cussing this question, it appears advisable to inquire whether 

 there is any eWdence which would corroborate the deduction 

 that it is a monatomic element. This evidence must be sought 

 for in the proiwrties of argon, for those of helium have not as 

 yet been sufficiently investigated. 



We know from countless examples among compounds of 

 hydrogen and carbon that increase in molecular weight is 

 accompanied by rise of boiling point ; and it may be stated as a 

 ])roved fact that a polymeride has always a higher boiling point 

 than the simpler molecule of which the p<jlymeride is formed. 

 Among the substances germain to this inquiry, ozone and 

 oxygen may be cited ; the complex molecule of ozone is shown 

 by the higher temperature at which it boils. It might be con- 

 cluded with certainty, therefore, that A,, could it exist, should 

 have a higher boiling point than -A,. 



Next, it is generally the case that the boiling ix)int of an 

 element, provided it has not a complex molecule like that of 

 sulphur and phosphorus, is lower, the lower its molecular 

 weight. There are the well-known instances of chlorine, 

 bromine, and iotlinc : but if it be objected that these all belong 

 to the same group, we may cite the cisesof hydrogen, - 243.5' • 

 nitrogen, -194.4': and oxygen, -1827°; and we may add 

 chl<irine, - 102°. If argon jwsscssed the atomic weight 20 

 and the molecular weight 40, it is probable that its boiling 

 point would lie above that of chlorine, instead of, as is actually 

 the fact, at - 187" — below that of oxygen. But, it may be 

 ■ '•■' ted, the Imiling |X)inl is determined, not by the molecular 

 1'. il;1u. but by the density. It maybe urged that the density of 

 .u,^'jii is 20, and that its molecules, like tho.se of oxygen 

 and nitrogen, arc diatomic, in spite of the argument to the con- 

 trar}- from the ratio of specific heats. The answer to this 

 ilpjection is obvious : if this were so, its boiling point should lie 

 .iKrve, and not l>elow that of oxygen. 



These considerations cannot, of course, be accepted as 



' evidence, but merely as corroborative of the conclusion as 



,...>r.|s the monatomicity of argon. If they a))ply to argon, 



.ipply with equal force to helium ; and if ihey are 



■ 1 ted, it follows that the atomic weight of helium is 4'26. 



It is again neccssar)' to consider the character of argon in 



attempting to answer the next question : .Are argon and helium 



.single elements or mixtures of elements? But before discussing 



il, let us consider anothers|ueslion : How does argon happen to 



' '■'■nr in the air and heliuhi only in minerals? Why is helium 



1 • 1 resent in air? A satisfactor)' anssver to this question is, we 



:mii!v, contained in a pajK-r by Dr. Johnstone Stoney (tV/cw;. 



iVnvs, 1895. Ixxi. 67). lie there shows that were hydrogen to 



be present in air (and it might Iw present, in spite of the oxygen 



rtith which it could be mixed, for a small €|uantity would surely 



e><-a|>e combination), it would, in virtue of the velocity of its 



r , .! ' ,T motion, remove itself from our ]>lanel, 



i.il body possessing .sufficient gravitational 



. ,:::.:;. Dr. .Stoney suggests this explanation to 



account fur the aljsencc of an atmosphere and of water vapour on 



the nifHin, and for the presence of an atmo-spherc of hydrogen 



'in the sun. 1 1 would also account for the absence of helium in 



<iur atmospliere. and for the presence of the chromospheric line 



'' ' ' ' ill can form compfiunds, or if il is 



hiun ap|K-ars to l>e, it will, like 



'••I "II the earth. 



'lid favour their existence in 

 in the atmosphere, precisely 

 iii|«>uhiU. Similarly nitrogen is a con- 

 in the first place those elements with 

 iirectly are comparatively rare, and also 

 liecausc such compounds are mostly decimiixised by water ; and 



NO. 1344, VOL. 52] 



I he mertnes^ 

 the free slatr. 

 lnraiMf it ' 

 >IitiR-rit <-! 

 which it C'liiiDiiic- 



the excess of nitrogen therefore occurs in the free state. 

 Similarly, the occurrence of free oxygen is due to the fact that 

 some remains over, after all or almost all the readily oxidised 

 substances have already united with oxygen. If there exist 

 gases similar to argon in inertness, they too may be looked for 

 in air. 



Now if argon possess the atomic weight 40, there is no place 

 for it in the periodic table of the elements. .And up to now 

 there is no exception to this orderly arrangement, if the doulitful 

 case of tellurium be excluded. Kaylcigh and Ramsay have show n 

 that the high density of argon c.in hardly be accounted for by 

 supposing that molecules of A„ are mixed with molecules of A, ; 

 and excluding as untenable the supiwsition that argon is a 

 compound, the only remaining suggestion is that it is a mixture. 

 No attempts ha\e as yet been made to test the correctness of this 

 idea ; but exi)eriments have already been started which, it is 

 hoped, will throw light on this question. 



The density of argon is too high ; to fill its place in tlie 

 periodic table, between chlorine and potassium, its density 

 should be about 19 and its atomic weight 38. We might 

 expect the presence of another element with a density of 41 

 and an atomic weight of 82. to follow bromine, as argon 

 follows chlorine ; and this element would probably also be a 

 gas, since its density would be only a little higher than that of 

 chlorine. 



But here we meet with a difficulty. There are certain lines 

 in the spectrum of helium coincident with lines in the argon 

 spectrum. There can be only one explanation, excUuling the 

 extremely improbable hypothesis, which is not verified in any 

 instance, that two elements may give spectra containing 

 identical lines. That, explanation is, of course, that each con- 

 tains some common ingredient ; and there appears to be a place 

 for one with density 10 and atomic weight 20, to follow 

 fluorine in the periodic table. The density of helium is, 

 however, so low, that there does not appear room for any 

 large quantity of a heavier gas ; and to fit the periodic table, 

 the density of argon should be diminished by removal of a 

 heavier admixture, rather than increased by removal of a 

 lighter one. 



Such are the jiroblems which now confront us. Until more 

 experiments have thrown further light on the .subject, we 

 regard it as labour lost to discuss the relations of these curious 

 elements to others which find their proper place in the periodic 

 table. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Sir Julian Goi.dsmid has been elected Vice-Chancellor 

 of the University of London, in succession to Sir James Taget, 

 who has resigned. 



Tut: new Directory n{ the Department of Science and -Art, 

 which has just come to hand, contains the regulations for 

 Organised Science Schools, previously referred to in these 

 columns. .Among other matter new to the Diredory, and an- 

 nouncements of changes, we notice that a new method of 

 according the Niitional .Scholarships is in contemplation. The 

 change will not take effect until the Session 1896-97, and 

 due intimation of its nature will be given. The .syllabus of 

 Practical Plane and Solid Geometry h.is been recast in the 

 elementary stage, in the direction already noted, and new sylla- 

 buses are given for Inorganic Chemistry, theoretical and practical. 

 Geology, anil I'hysiography. Il is not clear, however, wlaiher 

 the questions to be set for the examinations next -May will lie 

 based up^jn the new or the old .syllabuses. 



At the ordinary ipiarterly meeting of the Royal College of 

 Physicians of London, held on Thursday last, .Sir Rus.sell 

 Reynolds, K. R.S. , in the chair, the following gentlemen were 

 elected officers of the College :— Censors, Sir William II. 

 Broadl)ent, Dr. P. II. Pye-Smilh, Dr. T. Tillyer WMipliam, 

 Dr. William Cayley ; treasurer. Sir Dyce Duckwcirlli : emeritus 

 registrar, Sir I lenr)- Pitman ; registrar. Dr. IMward l.ivcing: 

 librarian. Dr. William Munk ; examiners— chemistry ami 

 chemical physics, Mr. Charles K. Groves, K.K.S., Mr. W. R- ' 

 Dunstan, .Mr. J. Millar Thimison, Dr. Samuel Kicleal, Dr. R. 

 Taylor I'limplon ; materia medica and pliuriiiacy. Dr. T. , 

 I.auder Brnnton, K.K.S., Dr. Daniel J. Leech, Dr. .Sidney I'. ] 

 Phillips, Dr. Frederick Willcocks, Dr. Krancis G. Penrose i 



