496 On the Natural Groupings of the Elements. 



teroxide and terchloride of iridium ? The atomic weight, the 

 atomic heat, and the atomic volume of gold are nearly the 

 doubles of those of platinum. 



Gold. Platinum. 



196-6 98-6 X 2 = 197-2 



6-37 3-19x2= 6-38 



128-0 57-0 X 2 = 114-0 



The atomic volume and atomic heat of silver are the same as 

 those of gold. These two last groups comprise all the metals 

 whose oxides are reduced to the nnetallic state by heat alone. 



It is observable that w^e have altogether thirteen triads of 

 similar elements, the ferric triad, and probably several others, 

 being double from the existence of twin elements, and the 

 platinic triad being incomplete. 



In each triad, the intermediate term is possessed of interme- 

 diate properties, and has an exactly intermediate atomic weight. 

 The mean differences or increments of atomic weight in the 

 different groups, are approximatively as follow; — 



Groups. Mean differences. 



Ferric 2 



Plumbic 4 



Yttric 14 



Silicic 14 



Sodic 16 



Zincic 20 



Molybdic 22 



Calcic 24 



Ceric 28 



Phosphoric ....... 44 



Chloric 44 



Platinic 44 



Sulphuric 48 



Moreover, with each of several of the triads is associated an 

 analogous element having an atomic weight approximatively one- 

 half that of the first member, or double that of the last member 

 of the triad. The former relation obtains in the chloric, sulphuric, 

 phosphoric, and possibly in the ferric groups — the latter in the 

 phosphoric, the silicic, the molybdic, the platinic, and possibly 

 in the ferric groups. 



The phosphoric triad is the only one that does not present 

 any relation in the atomic volumes of its members, a result pos- 

 sibly due to the allotropism of phosphorus. In the chloric, 

 sulphuric, ferric, and platinic groups, we have the relation of 

 equality ; in the sodic, calcic, zincic, and plumbic groups, the 

 relation of sequence. 



With the atomic weights that I have employed, we find the 

 atomic heats of the elements to be as follow: — 



