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444 DENTAL MEDICINE.

DENTAL FORMULA.
Dentifrice.
Dr. Sewell.
R Pulv. radicis iridis ^ss
Pulv. saponis cas
^ ij
Pulv. sodii boratis
^ ij
Cretse preparatse ^ ij. M.
Flavor with a few drops of oil of cloves and lavender. Or, add a
few drops of carbolic acid to each ounce of the powder, and flavor
the whole with eucalyptus oil. (For other dentifrices see Prepared
Chalk.)

ISONANDRA GUTTA—GUTTA PERCHA.
Source.—Gutta Percha is the inspissated juice of the tree
honandra Gutta.^ extensive forests of which are found in the East
Indies. It belongs to the natural order Sapotacece. It is in the
form of tough, flexible pieces, which have been freed from im-
purities by cutting it into thin slices, and then washing and tear-
ing it into shreds by heavy machinery while it is softened in boil-
ing water. It may be more thoroughly purified by dissolving it
in either chloroform, benzol or hot turpentine, thus causing the
impurities to separate, when it is evaporated to dryness. Crude
gutta percha is of a chocolate or reddish-brown color ; commer-
cial gutta percha is of a grayish-white color, and the variety which
has been purified by dissolving it in chloroform, etc., is almost
white, greasy to the touch, and of a leathery smell, like that of
India rubber. It is insoluble in water at any temperature, and is
a bad conductor of heat and electricity. At ordinary tempera-
tures it is tough, hard and inelastic, but toward 120° F. it softens,
and at 150° it becomes soft and plastic, and may be moulded into
any form, which it will retain on cooling, having, however, a
perceptible shrinkage. Gutta percha is dissolved cold by chloro-
form and sulphide of carbon; benzol requires the aid of heat, and
oil of turpentine requires to be quite hot. The alkalies have no
action upon it; but concentrated nitric acid attacks it rapidly,
with effervescence and the escape of nitrous fumes.