W. Crookes — Position of Helium, Argon, etc. 



Art. XIX. — On the Position of Helium, Argon and Kryp- 

 ton in the Scheme of Elements ;* by William Crookes, 

 F.R.S. 



It has been found difficult to give the elements argon and 

 helium (and I think the same difficulty will exist in respect to 

 the gas krypton) their proper place in the scheme of arrange- 

 ment of the elements which we owe to the ingenuity and 

 scientific acumen of Newlands, Mendeleef and others. Some 

 years ago, carrying a little further Professor Emerson Keynold's 

 idea of representing the scheme of elements by a zigzag line, I 

 thought of projecting a scheme in three dimensional space, and 

 exhibited at one of the meetings of the Chemical Society^ a 

 model illustrating my views. Since that time, I have re- 

 arranged the positions then assigned to some of the less known 

 elements in accordance with later atomic weight determina- 

 tions, and thereby made the curve more symmetrical. 



Many of the elemental facts can be well explained by sup- 

 posing the space projection of the scheme of elements to be a 

 spiral. This curve is, however, inadmissible, inasmuch as the 

 curve has to pass through a point neutral as to electricity and 

 chemical energy twice in each cycle. We must therefore 

 adopt some other figure. A figure-of-eight will foreshorten 

 into a zigzag as well as a spiral, and it fulfils every condition 

 of the problem. Such a figure will result from three very 

 simple simultaneous motions. First, an oscillation to and fro 

 (suppose east and west) ; secondly, an oscillation at right angles 

 to the former (suppose north and south), and thirdly, a motion 

 at right angles to these two (suppose downwards), which, in its 

 simplest form, would be with unvarying velocity. 



I take any arbitrary and convenient figure-of-eight, without 

 reference to its exact nature ; I divide each of the loops into 

 eight equal parts, and then drop from these points ordinates 

 corresponding to the atomic weights of the first cycle of ele- 

 ments. I have here a model representing this figure projected 

 in space ; in it the elements are supposed to follow one another 

 at equal distances along the figure-of-eight spiral, a gap of one 

 division being left at the point of crossing. The vertical 

 height is divided into 240 equal parts on which the atomic 

 weights are plotted, from H=l to Ur = 239*59. Each black 

 disc represents an element, and is accurately on a level with its 

 atomic weight on the vertical scale. 



* Read before the Royal Society, June 9; from an advance proof sent by the 

 author. * 



f Presidential Address to the Chemical Society, March 28, 18S8. 



