of procuring Potassium, 581 
as to contain twice as much iron turnings and potash, and have 
.employed it with success. But on the other hand, there are 
limits to this extension of the width, arising from the increased 
difficulty of making the heat penetrate throughout. 
The opening of the barrels at the top must be covered with 
a cap or wide tube, which being at a distance from the fire 
need only be fastened with sealing wax, but for the greater 
security of keeping this part cool, the whole of the tube which 
is out of the fire should be wrapped round with linen or blot- 
ting paper kept wet. 
The opening of the wide tube must be closed with a cork 
having a crooked tube of glass through it, containing a drop 
of mercury, which being moved by the passage of the air 
shews that the vessels are perfectly tight. But the annexed 
sketch will at once shew both the construction and dimensions 
of the apparatus. Glass tube. 
MDCCCXIV. 
