[ 24 ] 



II. On the Purification of Mercury by Distillation in vacuo. 

 By J„ W. Clark, Demonstrator of Physics in University 

 College, Liverpool*. 



[Plate I.] 



THE usual processes for the purification of considerable 

 quantities of mercury may be roughly classed as (i.) 

 chemical (e. g. treatment with dilute N0 2 (HO), Cr0 2 (H0) 2 , 

 Fe 2 Cl 6 , S0 2 (HO) 2 , and S0 2 (Hg0 2 ), &c.); (ii.) mechanical 

 (e. g. shaking, filtering through wash-leather, &c.) ; and (iii.) 

 distillation. The last-named process may be conducted either 

 in vacuo or under the ordinary pressure. 



Of these processes distillation in vacuo is in all respects the 

 simplest and most satisfactory. Preparatory to distillation 

 the mercury may be advantageously filtered through a writing- 

 paper cone with a very small orifice at the apex ; and when 

 considerable quantities of lead or zinc are present, the distilla- 

 tion in vacuo may be hastened by their previous removal by 

 one of the usual chemical methods. It is stated that the pre- 

 sence of yo o o o P ar ^ °f l eac ^ reduces the amount of mercury 

 distilled in a given time from 67 to 55f. Gold, iridium, silver, 

 copper, tin, nickel, cadmium, and arsenic do not influence the 

 rate of distillation^. 



The distillation of mercury under the ordinary pressure is 

 too inconvenient a process to be ordinarily used in laboratories; 

 not so, however, at a temperature of 18Q°-200° C. in vacuo. 

 The first apparatus for this purpose was described by Wein- 

 hold§, and since then Weber || and A, W. Wright If have de- 

 scribed other forms. The form shown in section in fig. 1 

 (Plate I.) differs from all the preceding chiefly in being sup- 

 plied with the mercury to be distilled from a movable reservoir 

 (in the form of a constant level regulator, fig. 2), the raising 

 of which fills the distiller with mercury, which thus renders 

 a Sprengel-pump unnecessary to set it in action. It is hoped 

 moreover that its simplicity and efficiency and the ease with 

 which it can be made may render its description useful. 



The distiller consists of a lead-glass tube, a b (fig. 1), 36 

 inches long, and about | of an inch in internal diameter. 

 A bulb of about two inches diameter is blown two inches 

 from its closed upper end. The lower end passes air-tight 

 through a well-secured india-rubber cork which closes the top 



* Communicated by the Physical Society. 



t Gmelin-Kraut, Ildb. der Chemie, Bd. iii. Abth. i. S. 740, 6te Auil. ; 

 Millon, Ann. Chim. Phys. [3] xviii. p. 337. 



X Gmelin-Kraut, loc. cit. 



§ Proqr. d. k. Gewerbsch. zu Chemnitz. Pep. fur Physih, Bd. xv. S. 1. 



|| Ibid. Bd. xv. S. 52. f Chem. News, 1681, p. 311. 



