M. D. Mendelejeff on the Discovery of Gallium. 545 



reduction ; its density will be about 5*9, its atomic volume 

 about 11*5 ; it will be fusible at a somewhat low temperature. 



It will not oxidize in air ; it will decompose water at a red 

 heat. The pure metal will not be easily attacked by acids or 

 by alkalies. The atomic volume of the oxide, El 2 3 , will be 

 about 5*5 : this oxide will be soluble in the stronger acids ; it 

 will form an amorphous hydrate insoluble in water, but dis- 

 solved by acids and by alkalies. 



The oxide of eka aluminium will form neutral and basic salts, 

 El 2 (OH . X) 6 , but not acid salts ; the alum, El K (S0 4 ) 2 12 H 2 0, 

 will be more soluble and less crystallizable than the correspond- 

 ing aluminium salt. The basic properties of El 2 3 will be 

 more distinct than those of Al 2 3 , but not so marked as those 

 of ZnO ; it will belong to that group of oxides which are pre- 

 cipitable by barium carbonate. The volatility and other pro- 

 perties of the salts of eka aluminium stand midway between 

 those of the salts of aluminium and of indium : it is probable 

 that the metal in question will be discovered by means of spec- 

 tral analysis, as was the case with indium and thallium. 



The characteristics of eka aluminium were deduced from a 

 consideration of the place occupied by this hypothetical ele- 

 ment in the periodic system : — 



SlpT*-|£iQ 



2nd 



3rd 



4th 



5th 



3. . 



group. 



• Mg 



group. 



Al 



group. 

 Si 



group 

 P 



5. . 



. Zn 



El 



Es 



As 



7. . 



. Cd 



In 



Sn 



Sb 



It ought to be remarked that, previous to the discovery of 

 the periodic law, it was not possible to predict the existence 

 or to foretell the properties of undiscovered elements. 



M. Lecoq de Boisbaudran has discovered, by means of spec- 

 tral analysis, the existence of a new element in the blende of 

 Pierrefitte (Pyrenees) ; to this element he has given the name 

 of gallium. The manner of its discovery, the process for its 

 separation (precipitation by sulphuretted hydrogen before zinc), 

 and certain of its properties (precipitation by barium carbonate, 

 solubility of the hydrate in ammonia, degree of volatility, &c), 

 make it probable that the new metal is no other than eka alu- 

 minium. 



If subsequent researches confirm the identity of the pro- 

 perties of gallium with those which I have pointed out as be- 

 longing to eka aluminium, the discovery of this element will 

 furnish an interesting example of the utility of the periodic 

 law. Let us hope that the discovery of eka silicium, Es = 72, 

 Es0 2 , the probable properties of which I have detailed in Lie- 

 big's Annalen, vol. viii. (Suppl.) p. 171, will not be long de- 



Phil. Mag. B. 5. No. 7. Suppl. Yol. 1. 2 



