oxide
liberated setting fire to the sugar, which goes on burning. Similarly,
phosphorus can be burned under water by covering it with a little
potassium chlorate and running in a thin stream of concentrated
sulphuric acid (see papers by Bray, _Zeit. phys. Chem._, 1906, et
seq.).

Chlorine heptoxide was obtained by A. Michael by slowly adding
perchloric acid to phosphoric oxide below -10 deg. C.; the mixture is
allowed to stand for a day and then gently warmed, when the oxide
distils over as a colourless very volatile oil of boiling-point 82 deg.
C. It turns to a greenish-yellow colour in two or three days and gives
off a greenish gas; it explodes violently on percussion or in contact
with a flame, and is gradually converted into perchloric acid by the
action of water. On the addition of iodine to this oxide, chlorine is
liberated and a white substance is produced, which decomposes, on
heating to 380 deg. C, into iodine and oxygen; bromine is without action
(see A. Michael, _Amer. Chem. Jour._, 1900, vol. 23; 1901, vol. 25).

Several oxy-acids of chlorine are known, namely, hypochlorous acid,
HClO, chlorous acid, HClO2 (in the form of its salts), chloric acid,
HClO3, and perchloric acid, HClO4. Hypochlorous acid is formed when
chlorine monoxide dissolves in water, and can be prepared (in dilute
solution) by passing chlorine through water containing precipitated
mercuric oxide in suspension. Precipitated calcium carbonate may be
used in place of the mercuric oxide, or a hypochlorite may be
decomposed by a dilute mineral acid and the resulting solution
distilled. For this purpose a filtered solution of bleaching-powder
and a very dilute solution of nitric acid may be employed. The acid is
only known in aqueous solution, and only dilute solutions can be
distilled without decomposition. The solution has a pale yellow
colour, and is a strong oxidizing and bleaching agent; it is readily
decomposed by hydrochloric acid, with evolution of oxygen. The salts
of this acid are known as hypochlorites, and like the acid itself are
very unstable, so that it is almost impossible to obtain them pure. A
solution of sodium hypochlorite (_Eau de Javel_), which can be
prepared by passing chlorine into a cold aqueous solution of caustic
soda, has been extensively used for bleaching purposes. One of the
most important derivatives of hypochlorous acid is bleaching powder.