APPENDIX III. 497 



of the elements in dependence upon their atomic weights, for there is no 

 reason on the basis of existing data, for admitting any intermediate elements 

 between Cl = 35*5 and K = 39, and all the positions above potassium in the 

 periodic system are occupied. This renders it very desirable that the velocity 

 of sound in argon should be re-determined. 13 



4. Argon was liquefied by Professor Olszewsky, who is well known for his 

 classical researches upon liquefied gases. These researches have an especial 

 interest since they show that argon exhibits a perfect constancy in its 



w If it should be found that Tc for argon is less than 1-4, or that k is dependent upon 

 the chemical energy, it would be possible to admit that the molecule of argon contains 

 not one, but several atoms for instance, either N 3 (then the density would be 21, which 

 is near to the observed density) or Xg, if X stand for an element with an atomic weight 

 near to 6*7. No elements are known between H=l and Li = 7, but perhaps they may 

 exist. The hypothesis A = 40 does not admit argon into the periodic system. If the 

 molecule of argon be taken as A 2 i.e. the atomic weight as A =20 argon apparently 

 finds a place in Group VIII., between, P = 19 and Na = 23 ; but such a position could only 

 be justified by the consideration that elements of small atomic weight belong to the 

 category of typical elements widen offer many peculiarities in their properties, as is 

 seen on comparing N with the other elements of Group V., or O with those of Group VI. 

 Apart from this there appears to me to be little probability, in the light of the periodic 

 law, in the position of an inert substance like argon in Group VIET., between such active 

 elements as fluorine and sodium, as the representatives of this group by their atomic 

 weights and also by their properties show distinct transitions from the elements of the 

 last groups of the uneven series to the elements of the first groups of the even series for 

 instance, 



Group vi. vn. vm. i. n. 



Cr Mn Fe,Co,Ni Cu Zn 



While if we place argpn in a similar manner, 



vi. vn. VHI. i. n. 



= 16 F = 19 A=20 Na=23 Mg = 24 



although from a numerical point of view there is a similar sequence to the gjbove, still 

 from a chemical and physical point of view the result is quite different, as there is no 

 such resemblance between the properties of O, F and Na, Mg, as between Cr, Mn, and 

 Cu, Zn. I repeat that only the typical character of the elements with small atomic 

 weights can justify the atomic weight A =20, and the placing of argon in Group VIII 

 amongst the typical elements ; then N, O, F, A are a series of gases. 



It appears to me simpler to assume that argon contains N 3 , especially as argon is 

 present in nitrogen and accompanies it, and, as a matter of fact, none of the observed 

 properties of argon are contradictory to this hypothesis. 



These observations were written by me in the beginning of February 1895, and on 

 the 29th of that month I received a letter, dated February 25, from Professor Eamsay 

 informing me that ' the periodic classification entirely corresponds to its (argon's) atomic 

 weight, and that it even gives a fresh proof of the periodic law,' judging from the 

 researches of my English friends. But in what these researches consisted, and how the 

 above agreement between the atomic weight of argon and the periodic system was arrived 

 at, is not referred to in the letter, and we remain in expectation of a first publication of 

 the work of Lord Rayleigh and Professor Ramsey. [For more complete information see 

 papers read before the Royal Society, January 81, 1895, February 13, March 10, and 

 May 21, 1896, and a paper published in the Chemical Society's Transactions, 1895, 

 p. 684. For abstracts of these and other papers on argon and helium, and correspon- 

 dence, see ' Nature,' 1895 and 1896.] 



