492 Hackh — Modification of the Periodic Table. 



four members of each period have polar numbers always 

 two units apart, e. g., 1-3-5-7, 2-4-6, 1-3-5, 2-4, etc., while 

 the polar numbers of the elements in the middle of a 

 period are odd and even. A survey of their compounds 

 show, that isomorphism is closely related to the polar 

 number of the elements. Thus the table of isomorphism 

 as given by Nernst can be completed as follows : 



Polar number 1 : Li-Na-K-Kb-Cs ; CuAg-Pd-Au-Hg-Tl. 



Polar number 2 : Be-Mg-Ca-Sr-Ba ; Zn-Cu-Ni-Co-Fe-Mn-Cr-V-Ti ; 



Cd-In-Sn; Hg-Pb. 

 Polar number 3 : B-Al-Sc-Y-La ; Sc-Ti-Y-Cr-Mn-Fe-Co-Ni ; 



Ga-In-Tl; La-Ce-rare earth, etc. 

 Polar number 4 : C-Si-Ti-Zr-Th ■ Ge-Sn-Pb ; etc. 

 Polar number 5 : N-P -As-Sb-Bi ; V-Cb-Ta. 

 Polar number 6 : S-Se-Te ; Cr-Mo-W-U ; Mn-Fe ; Ku-Rh ; 



W-Os-Ir. 

 Polar number 7 : F-Cl-Br-I ; Mn. 



We may take, for example, group 6, with the maximum 

 polar number 6 and find the following general formulas 

 for some of their compounds : 



— 2 : H 2 X = Hydrogen-x-ides, where X is S-Se-Te. 



+ 4 : X0 2 + H 2 = H 2 X0 3 = x-ites, resp. their salts where X 



can be practically each element. 

 + 6 : X0 3 + H 2 = H 2 X0 4 = x-ates, resp. salts. 



thus we have sulphates, selenates, tellurates, chromates, 

 manganates, molybdates, tungstates, uranates, ferrates, 

 etc., etc., in all of them X being hexavalent. Fig. 3 illus- 

 trates this relationship. We may e. g. take the bivalent 

 and trivalent elements and find two distinct series of com- 

 pounds : the metall-0^5 compounds, crystallizing all 

 with 7 mol. of H 2 and commonly known as the vitriols of 



(Ti) (Y) Cr Mn Fe Co Ni Cu Zn Mg(Be) 

 Mo Eh Pd Cd 



(W) Ir Pt 



all of them being soluble and forming double salts with 

 the elements of group 1. On the other hand we have the 

 metall-zc compounds of the simple formula M 2 (S0 4 ) 3 . 

 12H 9 which forms the well-known series of alumes 

 XM(S0 4 )o .24HoO where X is a monovalent metal or 

 NH 4 ' and M a trivalent element, either 



