482. A. W. Wright—Distillation of Mercury in Vacuo. 
glass tube which passes through it. The ring is fitted to the 
top of a common Bunsen burner, and the whole moves upon a ~ 
vertical slide, with a clamp screw, by which it may be fixed at 
any point desired. It has been found advantageous in practice 
to use but six of the openings, and these all upon one side. 
A conical hood of sheet copper encloses the upper half of the 
bulb, and is prolonged by a tube of the same material, which 
covers the glass tube as far as the angle above d. e lower 
edge of the hood is at nearly the same level as the top of the 
cylinder above mentioned, and is about six centimeters wider 
than this, so as to project laterally some three centimeters all 
round. The upper portion of the copper cone and tube are 
-wide enough to leave an interval of five or six millimeters 
between them and the glass. The heated gases from the holes 
in the cylinder, streaming through this space, envelop the bulb 
¢ and tube d, thus preventing condensation of the mercury 
vapor before it reaches e. | 
e cistern is mounted upon a vertical slide with a clam) 
screw, and can be moved up or down, the range of motion be- 
ing about six centimeters. This makes it possible always to 
bring the mercury to the proper height within the bulb, and to 
suit the adjustment to the varying atmospheric pressure. 
The apparatus is put in operation as follows: Connection 
having been established with a Sprengel air-pump by means of 
the tube 4 mercury is poured into the cistern so as to cover the 
bottom of it to the depth of a centimeter or two. If pure mer- 
cury is at hand the bulb at A may be filled with it, if not the 
extremity of the outlet tube is sealed or otherwise tightly 
sto . As the exhaustion proceeds the mercury rises in 4, 
finally reaching ¢, and if all the air were removed, it would 
stop at the barometric height above the surface in the cistern. 
The latter is adjusted so that the top of the column is a little 
below the center of the bulb, ¢. When no more air can be with 
drawn by the pump, fis sealed with a gas flame and the con- 
nection with the pump severed. e apparatus is thus exhaus- . 
ted once for all, as subsequently it maintains the vacuum by its 
own operation. The burner, previously set some distance below 
the bulb, is now lighted and the flame made very small at first. 
Tbe mercury soon becomes heated, vapor is formed, and after a 
time drops begin to fall from the interior surface of the bulb 
and tube above it. The flame is slowly increased and raised, 
until, in fifteen or twenty minutes, the vapor passes the angle 
at the top and begins to condense ine. As the globules of 
mercury fall into g they carry with them the residue of the air, 
gradually filling the bulb at A, and later the tube g itself. The 
point of the tube at A is now unsealed or broken off, and the 
- mercury issues drop by drop into a vessel placed to receive it. 
