THE OPERATIVE CHEMIST. 
276 
its external circumference, or base, depressed lower than its 
neck; so that the vapours which rise, and are condensed 
against its sides, by the contact of the surrounding air, runs 
down into the circular channel formed by its depressed part, 
from whence they are conveyed by the beak, or nose, on the 
side of the head or capital, into the receiving apparatus. 
The capital is sometimes stoppered, or pierced, that is to 
say, it has a small opening at the top, furnished with a 
ground stopper. This contrivance is convenient for intro 
ducing, from time to time, a fresh supply of materials in 
tended to be distilled, without deranging the apparatus. 
The capital, or head, is sometimes made air tight to the 
body by grinding, or even made of one piece with it ; but 
this method is expensive, and little, if at all, superior to 
closing the joint by lute. 
Some authors have directed the neck ofthe head to be placed within the 
mouth of the body ; but this would require them to be always ground to 
gether ; when the neck is blown of a proper roundness, it fits the outside 
of the body so as to require scarcely any lute. 
The alembic has this advantage over the common retort, that the resi 
dues of distillation may be easily cleared out of the body, which is not the 
case with the retort. It is likewise capable, when skilfully managed, of 
distilling a much larger quantity of liquid in a given time, than a retort of 
equal capacity. Besides this, the alembic may be used for causing the 
vapour of bodies to act upon substances in a more convenient manner 
than can be done by means of the retort and receiver. 
Glass bodies are usually made from one pint to two gal 
lons capacity ; and are occasionally pierced, and even stop 
pered on the side, at about half their height. They are 
sometimes made of earthenware, or pewter, and the head 
only of glass ; or of iron, with a stoneware head. A. silver 
body, with a glass head, is necessary for the preparation of 
the pure fixed alkalies, and with a silver head for preparing 
fluoric acid. 
Platinum bolt-heads, with heads of the same metal, are 
used in the concentration of oil of vitriol. 
These alembics are very expensive in the first instance ; 
that of Mr. Parke’s cost thrce hundred pounds ; but the fre 
quent accidents which happen, in concentrating the acid in 
glass, counterbalance the expense. 
It must be observed, that at the temperature in which this concentration 
is effected, lead unites with platinum, and they melt together. So that it 
has happened that some small grains of lead having fallen into a platinum 
alembic, have made holes through it : the utmost care should, therefore, be 
taken to avoid this mischance. But should it happen, the damage may 
be repaired by soldering in small plates of platinum by means of pure gold.