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IX. On the Atomic Weight of Beryllium. 

 By Bohuslav Brauner, Ph.D., of Prague*. 



HE question whether beryllium is divalent (Be // = 9*1) or 

 trivalent (Be f// = 13'65) is still a matter of interest for 

 chemists, although Nilsonf states that this question may be 

 regarded as completely settled in favour of trivalent beryllium. 



As this point is a vital one as regards the truth of the 

 periodic law, I venture to ask attention to the following 

 remarks. 



The history of this question will be found in the papers of 

 Nilson and Pettersson J, as well as in that of Humpsidge§; 

 and here I will mention only the most important points. 



In the year 1878 Messrs. Nilson and Pettersson found the 

 specific heat of beryllium to be 0*4083 between 0° and 100°; 

 and, in accordance with the law of Dulong and Petit, they con- 

 cluded that the atomic weight of beryllium is =13*8, and its 

 oxide represented by the formula Be 2 3 . 



Soon afterwards the author of the present paper [| published 

 a note, in which he pointed out that the following elements, 

 possessing small atomic weights, form an exception at ordinary 

 temperature to the law of Dulong and Petit: — boron, carbon, 

 magnesium, aluminium, silicon, phosphorus, sulphur, and 

 (in compounds in the solid state) hydrogen, nitrogen, 

 oxygen., fluorine. The writer concluded that in all proba- 

 bility beryllium (9*2), which stands close to boron (11), pos- 

 sesses an atomic heat of 3*8 instead of 6*4, and that it must 

 be placed among the eleven exceptions already mentioned. 

 At the same time it was remarked that the normal value of the 

 atomic heat may probably be reached at a somewhat higher 

 temperature. If, on the other hand, beryllium is considered 

 to be B /// = 13*8, this metal cannot be placed in Mendelejeff's 

 series. 



Nilson and Pettersson conclude, from their recent experi- 

 ments, that beryllium does not show any extraordinary rise of 

 atomic heat at a high temperature, and that it therefore does 

 not form an exception to the law of Dulong and Petit. The 

 same authors have also lately published a valuable research on 

 the molecular volumes and the molecular heats of the rare 



* Communicated by the Author, 

 t Berliner Berichte, xiii. p. 2035. 



\ Wiedemann's Annalen, iv. p. 554 ; Berl. Berichte, xi. pp. 381 & 906, 

 xiii. p. 1451. 



§ Chemical News, xiii. p. 261. 

 || Berliner Berichte, xi. p. 872. 



Phil. Mag. S. 5. Yol. 11. No. 65. Jan. 1881. F 



