Hackh — Modification of the Periodic Table. 491 



Elements combining with sulphur, forming typical 

 sulphides, are : 



Mn Fe Co Ni Cu Zn Ga Go As 

 Ag Cd In Sn Sb 

 Pd Hg Tl Pb Bi 



where the maximum of affinity is at Pd and decreases 

 gradually toward Mn, which has the lowest affinity for 

 sulphur.* 



The elements combining with hydrogen fall into two 

 distinct areas : 



(a) The nonmetals, giving gaseous or liquid hydrogen- 

 compounds in which hydrogen is positive. 



(b) The light metals, giving hydrides in the form of 

 salts, with hydrogen being negative. 



Elements combining with cyanogen (CN') and form- 

 ing characteristic radicals and cyanid-ions also occupy 

 neighboring places : 



Cr Mn Fe Co Ni Cu Zn 

 Mo — Eii Rh Pd Ag Cd 



Os Ir Pt An Tl 



Typical ammoniac compounds are formed by the ele- 

 ments around nickel : 



Co Ni Cu 



Pd Cd 



Pt 



These illustrations of the selective tendency or the 

 chemical affinity among the elements could be multi- 

 plied indefinitely, e. g., organometallic compounds, etc. 

 Closely related to this is the polar number, already men- 

 tioned, and the isomorphism. 



Table II has shown the positive or negative polar 

 numbers of the elements, and from it the periodicity of 

 the valence is clearly shown. It appears that the last 



* The affinity for sulphur is given as follows : Pd Hg Ag Cu Bi Cd Sb 

 Sn Pb Zn Ni Co Fe As Tl Mn, which forms a kind of a displacement series 

 of importance in mineralogy; see Schuermann, Liebig's Annalen, 249, p. 

 326, 1888. 



Weed, Eng. & Min. J., 50, p. 484, 1890. 



Van Hise, U. S. Geol. Surv. Monograph, 47, p. 1114, 1904. 



Buckley & Buehler, Missouri Bur. Geol., 4 (2d ser.), p. 90. 



Emmons, TJ. S. Geol. Surv., Bull. 625, 1917. 



