and on the Isomeric Modifications of Selenium, 497 



The product of this specific heat by the atomic weight 369*7, 

 usually given to nickel, is 41-00. It is probable that the specific 

 heat of pure nickel is considerably less, and that it does not 

 exceed 0-103. 



Sodium, 



My former researches on the calorific capacity of the binary 

 compounds, and of the salts formed by the alkaline metals, 

 showed that it was necessary to divide by 2 the atomic weights 

 which have hitherto been adopted by chemists*. Direct re- 

 searches on metallic potassium have led me since then to the 

 same conclusion f. It was of importance to verify this result 

 with metallic sodium, which is now procured so easily in a great 

 state of purity, and the manipulation of which does not present 

 so many difficulties as does that of potassium. M. Liebig sent 

 me, about six years ago, a certain quantity of sodium which he 

 had had expressly prepared for this purpose in his laboratory at 

 Giessen ; but my various occupations have until now prevented 

 me from making the experiment. I made determinations on the 

 sodium of M. Liebig which had been perfectly well kept in her- 

 metically sealed tubes, and on sodium recently prepared by M. 

 Rousseau. 



On breaking the tubes which contained the sodium of M. Liebig, 

 I was able to confirm the fact that the metal presented two very 

 distinct physical conditions. In the one, the sodium was per- 

 fectly malleable, could be bent in every direction without break- 

 ing, and presented no trace of crystallization. In the other, on 

 the contrary, the metal was extremely brittle, and exhibited in 

 its fracture pentagonal dodecahedra of the most perfect regularity. 

 These dodecahedra could be even detached from the mass with 

 the greatest ease, and presented then most perfect crystals, whose 

 diameter sometimes exceeded 3 millimetres. This difference was 

 owing probably to the presence of a small quantity of potassium. 



I cast the melted sodium under naphtha in a brass mould, 

 fig. 1. This mould is composed of a cylinder, 

 abcdj slightly conical, on which is screwed a bot- 

 tom, cdf pierced by a central hole, /. In this hole 

 is fitted a cylinder, also slightly conical. The 

 melted substance is run into the circular space; 

 when it has solidified on cooling, the bottom, cd^ is 

 unscrewed, the substance is taken out as well as 

 the cylinder e/, and the sodium is obtained in the 

 form of a cylinder bored in the direction of its 

 axis. The cylinder of sodium was wiped dry 

 immediately on cooling; the external surface 



* Annates de Chimie et de Physique, 3rd series, vol. i. p. 192 et seq. 



t Ibid. vol. xxvi. p. 266. 



