250 AN UNDISCOVERED GAS. 



tlie ratio of its specific heat showed that it, too, was a monatomic gas. 

 Its atomic weight, therefore, is identical with its molecular weight, viz, 

 4, and its place in the periodic table is between hydrogen and lithium, 

 the atomic weight of which is 7. 



The difference between the atomic weights of helium and argon is 

 thus 36, or 40 — 4. Now there are several cases of such a difference. 

 For instance, in the group the first member of which is fluorine we 

 have — 



Fluorine 19 -, ^ k 



Chlorine 35. 5 -, q" g 



Manganese 55 



In the oxygen group — 



Oxvgen 16 -.„ 



Sulphur 32 ^g ^ 



Chromium 52. 3"" 



In the nitrogen group — 



Nitrogen 14 -.„ 



Phosphorus 31 f,Q - 



Vanadium 51. 4 "^ ' 



And in the carbon group — . 



Carbon 12 -.^ o 



Silicon 28.3 J^-^ 



Titanium 48. 1 



These instances suffice to show that approximately the differences are 

 16 and 20 between consecutive members of the corresponding groups of 

 elements. The total differences between the extreme members of the 

 short series mentioned are — 



Manganese — Fluorine 36 



Chromium — Oxygen 36. 3 



Vanadium — Nitrogen 37.4 



Titanium — Carbon 36. 1 



This is approximately the difference between the atomic weights of 

 helium and argon, 36. 



There should, therefore, be an undiscovered element between helium 

 and argon with an atomic weight 16 units higher than that of helium 

 and 20 units lower than that of argon, namely 20. And if this 

 unknown element, like helium and argon, should prove to consist of 

 monatomic molecules, then its density should be half its atomic weight, 

 10. And pushing the analogy still further, it is to be expected that 

 this element should be as indifferent to union with other elements as 

 the two allied elements. 



My assistant, Mr. Morris Travers, has indefatigably aided me in a 

 search for this unknown gas. There is a proverb about looking for 

 a needle in a haystack; modern science, with the aid of suitable mag- 

 netic appliances, would, if the reward was sufficient, make short work 

 of that proverbial needle. But here is a supposed unknown gas, 

 endowed no doubt with negative properties, and the whole world to 

 find it in. Still the attempt had to be made. 



