Note 39 — Chapter XII · SODIUM

By dissolving sodium amalgams in water and acids, and deducting the heat of solution of the sodium, Berthelot found that for each atom of the sodium in amalgams containing a larger amount of mercury than NaHg5, the amount of heat evolved increases, after which the heat of formation falls, and the heat evolved decreases. In the formation of NaHg5 about 18,500 calories are evolved; when NaHg3 is formed, about 14,000; and for NaHg about 10,000 calories. Kraft regarded the definite crystalline amalgam as having the composition of NaHg6, but at the present time, in accordance with Grimaldi's results, it is thought to be NaHg5. A similar amalgam is very easily obtained if a 3 p.c. amalgam be left several days in a solution of sodium hydroxide until a crystalline mass is formed, from which the mercury may be removed by strongly pressing in chamois leather. This amalgam with a solution of potassium hydroxide forms a potassium amalgam, KHg10. It may be mentioned here that the latent heat of fusion (of atomic quantities) of Hg = 360 (Personne), Na = 730 (Joannis), and K = 610 calories (Joannis).