A. W. Wright—Distillation of Mercury in Vacuo. 479 
Art. LXI—An ra pte Jor the Ls ses Md Mercury in 
Vacuo; by ArtHUR W. WRI 
THE importance of pure mercury in many of the operations 
in the laboratory makes a simple and efficient means of free- 
ing from its impurities the ordinary commercial metal, or that 
which has become fouled by use, an object greatly to be de- 
sired. The familiar chemical methods , aside from their incon- 
venience, are not entirely satisfactory, and often leave the con- 
dition of the product uncertain. Distillation-in the usual way, 
stances volatile at the bo belitoe point of mercury. en the 
process is conducted in a vacuum, However, ‘these drawbacks 
are avoided, and a perfectly pure hemes is obtain 
A very elaborate and com plete apparatus for thi is purpose 
has bot devised by Professor Weinhold,* which fully satisfies 
all the conditions of the problem. This ihe Bhat has pro- 
visions for the maintenance of the vacuum eans of a 
Sprengel pump which constitates a special part of it, with 
suitable arrangements for adjustment of the mercury supply 
the heat from the gas burner, and the like. The devices for 
securing these objects, however, render the apparatus some- 
what bulky, and complicated i in structure. <A far simpler con- 
struction has been employed by Dr. L. Weber,+ which how- 
ever has no contrivance for maintaining or renewing the exhaus- © 
tion, except by refilling with mercury, and otherwise leaves much 
‘0 be desired: Its consists essentially of a long glass tube bent 
into a U-shape so that when filled with mercury and inverted 
with the ends of the tubes in vessels containing mercury it forms 
a double barometer, the bend of which is above the level of the 
metal and thereforé vacuous. An enlargement at one side 
where the heat is applied by a small Bunsen flame gives an 
increased surface of evaporation. The mercury vapor con- 
denses in ‘the upper portion of the empty space and flows out 
through the other branch of the tube. 
The pe uane devised by ‘He writer is based upon Weber's 
plan of a double barometer tube, but with important modifica- 
tions which secure substantially the Deractce s of the more 
complicated system of Weinhold. The most essential portions 
of it are me epryeeniets in section, in the accompanying sketch, 
| sd t 
o a scale of one-tenth that of the snatrament 
* Carl's ponies fiir Physik, vol. xv, p. 1. + Ibid., vol. xv, p. 52. 
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