The elements of materia medica and therapeutics: Plumbi oxydum. - Oxide of lead.

The elements of materia medica and therapeutics
by Jonathan Pereira, M.D. F.R.S. & L.S.
Fourth Edition, enlarged and improved, including notices of themost of the medicinal substances in use in the civilized world, and forming an Encyclopædia of Materia Medica.
Vol. I.
London: printed for Longman, Brown, Green, and Longmans, Paternoster Row.
1854.

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¹ De Morb. Mul. ii.

² Lib. v. cap. cii.

³ Hist. Nat. iixiv. 58.

⁴ Watson's Client. Essays, iii. 325, 6th edit.Formula PbO. Equivalent Weight 112.

History. — The ancients were acquainted with oxide of lead. Hippocrates¹ employed the semi-vitrified oxide (litharge,[]) . Dioscorides² ami Pliny³ both mention litharge: the latter calls it molybdaena.

Preparation. — Lead, when heated in the air so as to be converted into vapour, burns with a white light and forms oxide of lead, which, when thifc obtained, is called flowers of lead (flores plumbi). If melted lead be exposed to a current of air, it is rapidly oxidated and converted into the protoxide of this metal. The oxidated skimmings are denominated massicot. These, when fused at a bright red heat, are separated from some intermixed metallic lead; the fused oxide forms, on solidifying, a brick-red mass, which readily separates into crystalline scales: these constitute litharge (lithargyrum.) Litharge is obtained as a secondary product in the cupellation of ar gentiferous lead. The alloy is melted on a porous vessel, called a test or cupel (cineritum), and exposed to the blast of a bellows, by which the lead is oxidised, half vitrified, and driven off into hard masses of a scaly texture, and in that state is called litharge or silver stone.⁴

Properties. — Oxide of lead appears to be both dimorphous and amorphous. Thus it occurs in the form of pale yellow rhombic octohedra (dodecahedron, in that of red cubes, and also in that of a red amorphous powder. Both Houton-Labillardiere and Payen have obtained anhydrous oxide of lead in the form of white crystals. Its colour may be white, yellow, or reddish, according to the mode of preparation. As usually met with it is a pale yellow or reddish-yellow powder. There are several commercial forms of it. One of these is yellow, and is termed massicot (ceruxsa citritia). "When semivitrified (plumbi oxydum semicitreum, plumbi oxydum, D.), it is called litharge (lithargyrum). This occurs in the form of yellow or reddish scales or flakes, and, according to its colour, is called gold litharge (lithargyrum aureum vel chrysitis;) or silver litharge (lithargyrum argentum vel argyrilis). According to Leblanc red or gold litharge does not owe its colour to the presence of minium; for if it be melted and cooled suddenly it remains yellow, whereas if it be cooled slowly it acquires a red colour. Oxide of lead is fusible, and at a very high temperature volatile. It is almost insoluble in water. It is said that this liquid will take up about 1/1000th part of oxide, and that it acquires therefrom alkaline properties. Oxide of lead combines with alkalies and earths, forming salts called plumbites.

Characteristics. — Heated on charcoal by the blow-pipe, it is readily reduced to the metallic state. It is blackened by hydrosulphuric acid, formiug solphuret of lead, PbS. It is dissolved by dilute nitric acid, forming a solution of nitrate of lead, PbO,NO⁵, whose characteristic properties have been already stated. The varieties of the oxide are distinguished by their physical peculiarities.

Composition. — Oxide of lead is thus composed: —

	Atoms.	Eq. Wr.	Per Cent.	Berzelius.	Berthier.
Lead	1	104	92.837	92.828	93.3
Oxygen	1	8	7.143	7.172	6.7
---	---	---	---	---	---
Oxide of Lead	1	112	100.000	100.000	100.0

Purity. — The oxide of lead is enumerated among the articles of Materia Medica in the London Pharmacopoeia.

It is almost entirely soluble in diluted nitric acid. The solution is blackened by hydrosulphuric acid. That which is precipitated from this solution by potash is white, and is dissolved by an excess of the precipitant. From 100 grains of this oxide dissolved in nitric acid, and the solution precipitated by sulphate of soda, there are obtained in the dry precipitate 135 grains of sulphate of lead. — Ph. Lond.

Fifty grains dissolve entirely, without effervescence, in a fluidounce and a half of pyroligncous acid; and the solutiou, precipitated by 53 grains of phosphate of soda, remains prccipitablc by more of the test. — Ph. Ed.

he presence of a carbonate would be indicated by effervescence on the addition of acetic acid.

¹ Christison. op. cil. p. 509.Physiological Effects. — Inhaled in the form of vapour or fine dust, it produces the before-mentioned constitutional effects of lead. The effects of this substance, when swallowed, are but little known. It produces very slightly irritant properties. "The experimentalists of Lyons found litharge to be irritant in large doses of half an ounce."¹ From its external use ill consequences have sometimes resulted.

Uses. — Oxide of lead is never employed internally. Litharge is some times sprinkled over ulcers, as an astringent and desiccating substance. In pharmacy, it is used in the preparation of emplastrum plumbi, ceratrum naponis, acetas plumbi, and liquor plumbi diacetatis.

1. EMPLASTRUM LITHARGYRI, D. — (See post, Emplastrum Plumbi.)

2. CALCIS PLUMBIS; Plumbite of Lime. — This is prepared by boiling oxide of lead with cream of lime. Plumbite of lime is employed as a hair dye. The lead of the plumbite unites with the sulphur contained in the or ganic substance composing the hair, and forms the black sulphuret of lead.