510

ELEMENTS OF MATERIA MEDICA.

Plum'bi Oxydum. — Ox'ide of Lead .

History. —The ancients were acquainted with oxide {ox protoxide) oflead. Hippocrates {Be Morb. Mul. ii.) employed the semi-vitrified oxide{litharge, \i2<xpyvpoi). Dioscorides (lib.v. cap. cii.) and Pliny {Hist. Nat.xxxiv. 53) both mention litharge : the latter calls it molybdcena.

Preparation. —Litharge is usually obtained as a secondary productin the cupellation of argentiferous lead. The alloy is melted on a porousvessel, called a test or cupel, and exposed to the blast of a bellows, bywhich the lead is oxidized, half vitrified, and driven off into hard massesof a scaly texture, and is called, in that state, litharge or silver stone(Watson’s Chem. Essays, iii. 325, 6th ed.)

The compound called in the London Pharmacopoeia hydrated oxide oflead (plumbi oxydum hydratum ) is prepared by mixing six pints (or asmuch as may be sufficient) of solution ofpotasli with six pints of solutionof diacetate of lead and three gallons of distilled water. The precipi-tate is to be washed until nothing alkaline remains. In this process thepotash combines with acetic acid, and forms acetate of potash, whichremains in solution; while a white compound, called by Mr. Phillipshydrated oxide of lead, is precipitated. But it is stated, that “ oxideof lead does not form a hydrate with water, the white powder whichcaustic alkalies throw down in solution of lead being a basic (sub) salt”(Geiger’s Handb. d. Pharm. von J. Liebig).

Properties. —Oxide of lead presents itself in several forms. One ofthese is yellow, and is termed Massicot (cerussa citrina). When semi-vitrified {plumbi oxydum semivitreum), it is called litharge {lithargyrum ),which occurs in the form of small yellow or reddish scales or flakes,and, according to its colour, is called gold or silver litharge {lithargyrumaureum [chrysitis] sen argenteum [ argyritis ]). The plumbi oxydumhydratum, Pli. Lond., is a perfectly white powder.

Oxide of lead is fusible, and at a very high temperature volatile. Whenheated in contact with charcoal or carbonaceous bodies, it is readilyreduced to the metallic state. It is insoluble in water.

Characteristics. —Heated on charcoal by the blowpipe, it is readilyreduced to the metallic state. It is blackened by hydrosulphuric acid,and completely dissolves in nitric acid. The characteristics of this solu-tion have been already described {vide p. 505). The varieties of theoxide are distinguished by their physical peculiarities.

Composition. —Oxide of lead is thus composed:—

Eq. Eq.Wt. PerCent. Berzelius . Berthier.

Lead. 1 .... 104 .... 92-85 .... 92'85 .... 93'3

Oxygen ..... 1 .... 8 .... 7*14 .... 7-15 .... 6-7

Oxide of Lead . 1 .... 112 .... 99'99 .... lOO'OO .... 100-0

Physiological Effects. —Inhaled in the form of vapour, or fine dust,

it produces the before-mentioned constitutional effects of lead {videp. 506).

The effects of this substance, when swallowed, are but little known.It possesses very slightly irritant properties. “ The experimentalists of