166 PROF, W. J. SOLLAS ON A PROCESS FOR [May 1902, 
stopper having first been securely fitted in, heavy fiuid of the 
required specific gravity is introduced, till it fills the vessel up to the 
level of the greatest width of the upper part: 2 or 3 grammes of the 
powdered rock are then 
Apparatus for separating minerals of added, the upper stopper 
different specific gravity. inserted, and the whole 
7 well shaken. The sepa- 
| rator is laid horizontally 
on the table till separa- 
tion appears complete; it 
is then tilted slowly into 
the vertical position ; is 
again shaken, and left to 
stand. The separation 
will be the more complete 
the more frequently the 
fluid is agitated. As 
there may be a slight 
leakage at the lower 
end, the separator is 
placed to stand in a 
beaker, resting in a 
gently inclined position, 
so as to offer as large a 
surface as possible to the 
floating powder. When 
the separation is nearly 
complete the separator is 
restored to the vertical 
position, so that all the 
heavier material may find 
its way into the lower 
leg. The upper stopper 
is then removed, and the 
middle stopper gently 
pushed through the layer 
of floating material, the 
open end of the canal 
traversing it being kept closed by the thumb. After passing 
through the upper layer, the stopper may be washed to free it 
from adhering grains by carefully moving it from side to side 
in the clear fluid below; directly it appears to be clean it may 
be suddenly dropped into place. Experience shows that it does 
not carry down any appreciable quantity of the supernatant grains. 
The separator is next placed in a conical glass vessel—the re-, 
ceiver—having a constriction near its base, into which the lower 
stopper fits by its head. By gently rotating the separator to and 
fro the stopper is set free, and the heavier material may be 
removed from the lower leg. If this should not be present in large 
amount it will flow out along with the heavy fluid, as the thumb is 
