The elements of materia medica and therapeutics: Plumbi oxydum rubrum. - Red 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 Hist Naturalis, lib. xxiiii. cap. 40, ed. Valp.

² Idem.

³ Lib. v. cap. 109.Formula Pb₃O₄=2PbO, PbO₂. Equivalent Weight 344.

History. — It is doubtful whether the ancients were acquainted with this compound, as the substance which Pliny¹ called minium was cinnabar. He describes, however, an inferior kind, which he terms minium secundarium,² and which may be, perhaps, the red oxide of lead. Dioscorides³ distinguished minium from cinnabar. Besides minium, there are several other names for red oxide of lead. In commerce it is usually known as red lead. It is sometimes termed deutoride of lead, or the plumbate of the oxide of lead.


Natural History. — Native minium is found in Yorkshire, Suabia, Siberia, and some other places.

¹ Graham, Elements of Chemistry.Preparation. — Red lead is prepared by subjecting protoxide of lead (massicot or litharge) to the combined influence of heat and air, It absorbs oxygen and is converted into red lead. A heat of about 600° is necessary, The finest minium is procured by calcining the oxide of lead obtained from the carbonate.¹ [Besides the "red" there is also a superior quality, called "Orange" in commerce, the chemical distinction of which from the "red" has not been accurately determined. The value of the Orange is £36 per ton com pared with the "Red" at £25 per ton. — Ed.]

Properties. — Red oxide of lead has a brilliant red colour. By heat it gives out oxygen gas, and is converted into the protoxide of lead. Its sp. gr. is 8.62.

Characteristics. — By a strong heat it is converted into oxygen gas and the yellow oxide (PbO). Before the blowpipe on charcoal it yields first the yellow protoxide, and then metallic lead. When digested in nitric acid, the nitrate of the protoxide is obtained in solution, while the insoluble brown or peroxide of lead, PbO3, remains. By the action of sulphurous acid on red lead, white sulphate of the protoxide is obtained. 2PbO,Pbo₂ + SO₂= 2PbO + PbO,SO₃.

"Entirely soluble in highly-fuming nitrous acid; partially soluble in dilated nitric acid, a brown powder being left." — Ph. Ed.

Composition. — The composition of real or pure red lead is as follows: [puuttuu]

² Ann. dt Chim. et de Phys. xlix. 398.

3 Phil. Mag. N. S. iii. 125.Dumas² has shown that red lead of commerce is not uniform in composition, but consists of variable mixtures of real red lead with protoxide. His resells have been confirmed by those of Mr. Phillips.³ That real red lead is not a mere mixture of protoxide and peroxide is apparently shown by its colour, as well as by the fact that it is not altered by heating it in a solution of acetate of lead, which is capable of dissolving free protoxide. The following formulae represent the composition of different species of minium: 2PbO,PbO₂; PbO,PbO₂; 5PbO,PbO₂; 3PbO.PbO₂.

Adulteration. — Commercial red lead is sometimes adulterated with earthy substances (as brick dust), or red oxide of iron. Gélis and Fordos propose to detect this by boiling the suspected minium in water, with sugar, and a small quantity of nitric acid. The minium is entirely dissolved if it be pure, leaving the foreign matters.

Physiological Effects and Uses. — Its effects are similar to the protoxide of lead. It is but little employed in pharmacy. The Edinburgh College directs it to be employed in the preparation of aqua chlorinii (see ante, p. 885).