198 
ORIGINAL COMMUNICATIONS. 
partly precipitated. In this operation, a part of the potash is 
decomposed and yields its oxygen to a portion of the iodine, 
thus forming iodous acid; this latter combines with the unde- 
composed alkali, forming iodite of potassa. At the same time 
the potassium arising from the deoxidation of the potassa, com- 
bines with another portion of the iodine to form iodide of potas- 
sium. This product is evaporated to dryness, and mixed with 
a sixth part its weight of pure charcoal, and heated in a cruci- 
ble to a low red heat. The iodide experiences no alteration, 
but the iodite is decomposed, the oxygen of the acid and base 
uniting with the carbon to form carbonic acid; whilst the 
iodine and potassium also combine in the state of an iodide. 
When the operation is finished, which may be known, by 
the mass no longer scintillating on being stirred, the product 
is to be removed from the crucible, and dropped into about 
three or four times its weight of distilled water. The iodide 
is rapidly dissolved, whilst the undecomposed charcoal re- 
mains suspended in the fluid. The solution is to be filtered 
and evaporated in a glass capsule, till a slight pellicle is formed, 
and then permitted to cool slowly. The crystals thus obtain- 
ed must be drained, dried in a stove and kept in closely stop- 
ped bottles. 
It should always be borne in mind, that to obtain a perfect- 
ly pure and colourless iodide, it is absolutely necessary, that 
during its preparation it should not be exposed to the ac- 
tion of any acid vapour, and more especially chlorine gas, 
otherwise the iodide will be more or less ioduretted and of a 
yellowish colour. 
Caustic potassa. M. Cottereau gives the following 
advice respecting this article. Whenever any of it is removed 
from the bottle in which it is kept, the mouth of the bottle 
and the stopper should be washed with a wet sponge, and then 
carefully wiped dry, for if any particles should adhere to the 
ground surfaces, it will cause such a union between them as to 
render it almost impossible to remove the stopper. 
R. E. G. 
