5J4 M. D. Mendelejeff on the Discovery of Gallium. 



2. The periodic law demands a change in the atomic weights 

 of certain metals which have not as yet been sufficiently studied. 



Atomic weights of the metals 

 and formula? of their oxides. 



. A . 



Old numbers. Numbers pro- 

 posed by me. 



Indium 



'olnO 



113In 2 3 



Uranium 120 U 2 3 240 U0 3 



f The specific heat, deter- 

 mined by Bunsen, and 

 likewise by me, has 

 confirmed the change 

 (Bull, de VAcad. ht. 

 Petersbotirg, vol. viii. 

 p. 45). 



fRammelsberg and 



Roscoe have accepted 



j the change (Ber. der 

 dcut. chem. Ges. vol. 



Cerium * 92CeO 



Ce,0, 



138Ce,0, 



CeO./ 



Thorium UGThO 232ThO, 



Yttrium G0YO 90Y„O 3 



Erbium 114ErO 171Er~ 2 3 



SttSfp"} ab - t92RO 138R *°* 



I v. p. 1003, and vol. vii. 

 I p. 1131). 



The specific heat of the 

 metal (Bull, de VAcad. 

 St.Pete?'sbourr/,xo\.xm. 

 p. 45) and the consti- 

 tution of its salts (Lieb. 

 Ann. vol. clxviii. p. 46) 

 appear to confirm my 



, proposal. 



fOhydenius and Delafon- 

 J taine have, previously 



} to me, proposed the 



[ same alteration. 



fCleve (Ber. der dcut. 

 J chem. Ges. vol. viii. 



} p. 129) has accepted 



I my formulae R 2 3 . 



3. The periodic law indicates vacancies in the classificatory 

 scheme of the known elements, and enables us to predict the 

 properties of elements, as yet undiscovered, and of their com- 

 pounds. For example, there are two vacancies in the third 

 and fourth groups respectively of the fifth series : I have called 

 the unknown elements which should fill these vacancies Eka 

 aluminium, El, and Eka silicium, Es. 



The properties of eka aluminium, according to the periodic 

 law, should be as follows. Atomic weight about 68 ; formula 

 of its oxide El 2 3 ; its salts have the general formula El X 3 . 

 Thus, for example, the chloride of eka aluminium will be E1C1 3 ; 

 on analysis it will yield 39 per cent, of metal and 61 of chlo- 

 rine ; and it will be more volatile than ZnCl 2 . 



The sulphide, El 2 S 3 , or the oxysulphide, El 2 (S, 0) 3 , ought to 

 be precipitable by sulphuretted hydrogen and to be insoluble 

 in ammonium sulphide. The metal will be easily obtained by 



