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Dr. A. 0. Rankine on tin 



iodine. These two sets of gases are adjacent in pairs in the 

 Periodic Table. 



The molecular radii of these gases, calculated in the way 

 above indicated, are shown in the following table: — 



Table I. 



Gas. 



Molecular 

 radius XlO 8 cm. 



Gas. 



Molecular 

 radius XlO 8 cm. 



Ratio. 



Chlorine 



Bromine 



1-60 

 1-71 



18S 



Argon 



Krypton ... 

 Xenon 



1-28 

 1-38 

 1-53 



1-25 

 1-24 

 1-23 





The figures reveal the notable fact that the dimensions of 

 each corresponding pair of gases in the two groups are in 

 constant proportion, the numbers in the last column being 

 practically equal. In other words, we may say that the 

 radius of the molecule of a halogen gas is 1*24 times as 

 great as the molecular radius of the corresponding inert gas. 

 This statement is, of course, based upon the assumption that 

 all the molecules are spherical. 



The cube of 1*24 is 1*91, or practically 2. This means 

 that the halogen molecules have practically twice the volume 

 of the corresponding inert molecules. 



The molecular masses are also approximately in the pro- 

 portion of 2 : 1, for the atomic masses of corresponding gases 

 are nearly equal, the halogens being diatomic and the inert 

 gases monatomic. We should thus expect the densities of the 

 molecules of, for example, iodine and xenon to be equal, and 

 a similar equality for the other pairs. This is set forth in 

 detail in the followino- table. 



Table II. 



Pair oi' Gases. 



Ratio of 



Molecular Masses 



(from molecular weights). 



Ratio of 



Molecular Densities 



(from viscosities). 



Chlorine : Argon ... 

 Bromine : Krypton. 

 Iodine : Xenon 



1-78 

 1-03 

 1-95 



0-93 

 1-01 

 102 



