On Iodine. ~ 163 
then inverted. The heat of a charcoal chaffer being now applied, 
the iodine sublimes in great abundance. To prevent the heat 
from acting on the globular receiver, a thin dise of wood, with 
a round hole in its centre, is placed over the shoulder of the 
matrass. As soon as one globe becomes hot, another may be 
substituted in its place} and thus two or three may sérve in ro- 
tation to condense a yery large quantity. The iodine is easily 
washed out bya little water. It is then drained on glass plates, 
and dried. From the above twelve ounces of liquid I usually 
obtained about 200 grains of iodine. This may be purified by 
a second sublimation from dry quicklime. The most convenient 
apparatus is that represented (Plate III. fig.1.) It is composed 
of an exterior vessel J, containing the mixed materials, and an 
interior one a, filled with cold water. On the outside of a, beau- 
tiful large crystals concrete, and by lifting up @ they may be 
readily detached without breaking them. If in the operation of 
subliming the water of a should become hot, it is easy to run 
it off with a siphon, and to fill it again with cold, or to put into 
it some ice. J have not seei any such apparatus described be- 
fore, and I ean recommend it as possessing many advantages 
over the subliming vessels usually employed. 
If the manganese be increased much beyond the above pro- 
portion, the product of iodine is greatly lessened. If, for example, 
tlhirice the quantity be used, a furious effervescence ensues; nearly 
the whole mixture is thrown out of the matrass with a kind of 
explosive violence; and hardly any iodine is to be procured, even 
though the materials should have been saved by putting them 
into avery large vessel. On the other hand, should only one- 
half of the prescribed quantity of manganese be used, much hy- 
driodic acid rises along with the iodine, and washes it perpetually 
down the sides of the balloon, Or, if during the successful 
sublimation of iodine the weight of manganese be doubled, the 
violet vapours instantly cease. Neither sugar nor starch re- 
stores to the mixture the power of exhaling iodice vapour. 
A similar interruption of the process is occasioned by using an 
excess of sulphurie acid. For, if to the mixture of twelve ounces 
of saturated liquid, and 1000 grains manganese, an additional 
half-ounce measure of sulphuric acid be poured in, the violet 
vapour disappears, and the sublimation of iodine is finally stopped. 
Quicklime, added so as to saturate the excess of sulphuric acid, 
does not renew the process. In these two different cases, iodic 
acid is probably formed by the too rapid and copious supply of 
oxygen. For the due decomposition of hydriodic acid, the oxy- 
gen ought to be afforded merely in the quantity requisite to sa- 
turate its hydrogen. 
The best subliming temperature is 232° Fahr.; though in epen 
L 2 vessels 
