140 CHEMICAL DISCOVERY AND INVENTION 



Group I any elements finding a position therein would have a 

 valency one unit less than 1 or 0. 



The differences between the first and second lines are pretty 

 constantly equal to very nearly 16 units, thus 23-6-94 = 16-06, etc. 

 The differences between the second and third lines are at first 

 about 16, but increase in passing from left to right. If helium 

 and argon are introduced into such a table it is at once observed 

 that there is an interval between them which would apparently 

 require an element having an atomic weight 16 units greater 

 than that of helium, or approximately 20. The question then 

 arises does such an element exist ? 



This question Ramsay set to work to investigate. Many 

 fruitless experiments were undertaken on the gases obtained 

 from minerals and in attempts to separate helium and argon 

 into two gases by process of diffusion. The gases found in 

 many mineral waters, such as the hot springs at Bath, and the 

 waters of Cauterets in the Pyrenees in which argon and helium 

 had been found. The production of liquid air on a large scale 

 provided the material from which the first success was obtained ; 

 and, after allowing about a litre of it to evaporate away, the 

 last portions were found to contain a gas having about twice the 

 density of argon to which the name Krypton (Gr. hidden) was 

 given. Very shortly afterwards, by liquefying a large quantity 

 of " argon," obtained from atmospheric air, and in a similar 

 manner allowing the liquid to evaporate, the successive fractions 

 yielded two other gases. The one lighter than argon fitted the 

 place already prepared for it in the periodic table, the other had 

 a density of 64, and was found in small quantity in the least 

 volatile portions of the liquid, and was named Xenon (the 

 stranger). The complete story of these wonderful researches 

 by Lord Rayleigh and Professor Ramsay deserves to be read in 

 the original papers by every serious student of chemistry. The 

 details of the countless experiments, the ingenuity in devising 

 apparatus, the skill involved in its manipulation, and the know- 

 ledge which could turn to account so many physical facts and 



