IODIC ACID. 119
solved potassium perchlorate on a filter and recrystallize it from
200 c.c. of water. Yield, 30 g. The potassium chloride passes
into the filtrates.
1Potassium perchlorate, like the chlorate, yields no precipitate
with silver ions.
Heat in a dry test-tube a mixture of potassium chlorate and one-
sixth of its weight of manganese dioxide, and test the oxygen
evolved with a glowing splinter. Observe that the evolution of
oxygen takes place at a lower temperature than when pure potas-
sium chlorate is used. Extract the residue with water, and filter;
potassium chloride is in the filtrate, as may be shown with silver
nitrate.
Free perchloric acid is not explosive. Potassium perchlorate
when covered with concentrated sulphuric acid remains unchanged
in the cold and does not explode on gentle heating; potassium
chlorate, on the other hand, yields explosive chlorine dioxide even
in the cold. Pure perchloric acid, or a perchlorate mixed with
concentrated sulphuric acid, must be handled with caution, since
if it comes in contact with any oxidizable matter when warm
it explodes with great violence.- Iodic Acid and Iodic Anhydride; a "Time Reaction."
Seal a 0.5-1.0 meter long glass extension tube to the neck of a
round-bottomed flask, and boil 32 g. of iodine with 130 g. of con-
centrated, colorless nitric acid in the flask, using a ring burner to
avoid bumping. Remove the lower oxides of nitrogen, as fast as
they are formed, by means of a current of carbon dioxide, or of air.
After the oxidation is complete and the solution has cooled, collect
the solid iodic acid on an asbestos filter and separate it from the
asbestos fibers by dissolving in the least quantity possible of hot
water and filtering. Allow the iodic acid, HIO3, to crystallize,
after concentrating somewhat if necessary, by letting the solution
stand in a vacuum desiccator over sulphuric acid. Evaporate the
mother-liquor and dehydrate the residue at 200°. Iodic anhy-
dride, I2O5, is thus obtained.
Heat a sample of the iodine pentoxide in a test-tube; it is broken
down into iodine and oxygen, as is shown by the violet vapors and
by the test with a glowing splinter.
(^1) At the room temperature about 36 g. KC1, 6.6 g. KC1O
3 , and 1.5 g. KCIO4
are soluble in 100 c.c. of water.