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552 DISCOLORED TEETH AND THEIR TREATMENT.

ally classified with the chlorin methods, as the decomposition was sup-
posed to take place according to the following equation :

Allele + 3HA = Al A + SH^O + 6C1.

Experimental study of the reaction between aluminum chlorid and
hydrogen dioxid by the writer developed the fact that oxygen and not
chlorin was given off, and that the aluminum chlorid was unaltered
during the process. Hence it was discovered that the reaction was
simply due to a catalytic action of the aluminum salt (a property
which in this relation it shares in common with many other metallic
salts), whereby nascent oxygen is liberated from the hydrogen dioxid.
The process, therefore, has no greater value than those in which hydro-
gen dioxid is directly applied. The aluminum chlorid being an active
coagulant is contraindicated as a factor in tlic bleaching process until
a point has been reached where a coagulant is needed as a fixative after
the bleaching has been effected.
The Sodium Dioxid Method.—Sodium dioxid, NajO^, is the chem-
ical analogue of hydrogen dioxid, and like the latter is characterized
by the readiness with which it parts with its atom of loosely com-
bined oxygen under similar circumstances. The essential difference in
its properties is the character of its by-product after its decomposition
has taken place. Itself a strong caustic alkali, it still retains its alka-
line and caustic properties after the loss of one of its atoms of oxygen,
becoming NagO, which in combination with water is ordinary sodium
hydroxid or caustic soda. This substance as well as the sodium dioxid
has not only a saponifying property for all of the vegetable and animal
oils and fats, but also a solvent action upon animal tissue. This property
is of great value in removing from the dentin structure all of the con-
tained organic matter, whether normal or in a state of decomposition.
Having the oxidizing and consequently the bleaching quality in addi-
tion to its solvent and saponifying properties it is, therefore, one of the
most valuable bleaching and detergent agents at our command. The
substance is dispensed as a yellowish white powder in tin cans or
glass bottles hermetically sealed, as it is very hygroscopic and after
twenty-four hours' exposure to moist air absorbs nearly its own weight
of water ; it also loses much of its activity.
For use as a bleaching agent it is applied to the dentin in saturated
solution. In making the solution especial care is necessary in order to
avoid elevation of temperature, by reason of the energy with which it
enters into combination with the water. If the solution is allowed
to become heated in the making, decomposition of the compound with
loss of oxygen occurs and its bleaching power is destroyed. The