(Caustic Soda; Soda. U. S. P., 1890.)

Origin. - Prepared from a solution of soda in the same manner as described under Potassii Hydroxidum.

Description and Properties. - Dry, white, translucent pencils or fused masses, showing a crystalline fracture, odorless, and having an acrid and caustic taste. Great caution is necessary in tasting and handling it, as it rapidly destroys organic tissues. Exposed to the air, it rapidly deliquesces, absorbs carbon dioxide, and becomes covered with a dry coating of carbonate. Soluble in I part of water, very soluble in alcohol. Soda should be kept in well-stoppered bottles made of hard glass. Used externally.

Physiological Action and Therapeutics. - Potassii hydroxidum is one of the strongest and most penetrating caustics known. It possesses the property of abstracting water from the tissues, neutralizing free acids, decomposing nitrogenous compounds, and of forming solutions of fibrin, albumin, and gelatin.

When applied to the soft tissues it occasions severe pain, and produces a moist, ashen, and then black, leathery slough, which leaves a granulating ulcer behind it.

When potassium hydroxide is taken internally in immoderate doses it produces all the symptoms of corrosive poisoning. Small doses, freely diluted, have the same action as the alkalies.

As a caustic, potassa is used for the same purposes as the caustics previously described.

The action and therapeutics of sodium hydroxide are identical with those of potassa, save that soda is less depressing to the heart, muscular and nervous systems. It is not used so much as potassa, the latter preparation usually being preferred as a caustic.

To limit the caustic action of these drugs a piece of adhesive plaster should be applied first, with an aperture of the size desired.

Upon the skin exposed in the hole in the plaster the caustic is placed, the skin having been previously moistened. The caustic action may be arrested at any time by wetting the part with vinegar.