PLUMBI OXIDUM - OXIDE OF LEAD - LITHARGE, PbO, = 223.

Preparation

By roasting lead ores with access of air, when the oxide is formed in a melted state, and separates on cooling.

Characters And Tests

Occurs in small glistening red or yellowish-red scales, which should dissolve without effervescence in dilute acids, but after exposure for some time to the air, the scales slowly absorb carbonic acid and may then give some effervescence; they are soluble also in excess of potash.

The following tests are applicable to this, and to all soluble salts of lead: - (1) Sulphuric acid and soluble sulphates give a white precipitate (sulphate of lead) insoluble in dilute acids; (2) iodide or chromate of potassium gives a yellow precipitate of iodide or chromate of lead; (3) sulphuretted hydrogen or sulphide of ammonium gives a black precipitate of sulphide of lead, but if the proportion of lead be minute, the color is brown rather than black (W. G. Smith).

PLUMBI ACETAS - ACETATE OF LEAD - "SUGAR OF LEAD," Pb1C2H3

Preparation

By dissolving lead oxide in slight excess of acetic acid by aid of gentle heat, then crystallizing.

Characters

Occurs in white crystalline lumps, not unlike sugar, or in large four-sided prisms. The odor is somewhat sweet and acid, and the taste at first sweet, afterward astringent. It effloresces in air, and is soluble in water; with distilled water the solution is clear, but with ordinary water it is turbid from the formation of carbonate of lead with the alkaline carbonates always contained in such water; a few drops of acetic acid will dissolve the carbonate and clear the solution.

LIQUOR PLUMBI SUBACETATIS-SOLUTION OF SUBACETATE OF LEAD - "GOULARD EXTRACT," Pb(C2H3O2)2PbO(in water), = 548.

Preparation

By boiling neutral acetate of lead with two-thirds of its weight of oxide of lead, then filtering, and adding distilled water: a basic or subacetate of lead is formed.

Characters

A colorless liquid of alkaline reaction and sweetish astringent taste. It quickly absorbs carbonic acid from the air, and becomes turbid from formation of carbonate. It gives precipitates with most vegetable coloring matters, with tannin, and with many animal substances, especially albumen. With gum it forms an opaque white jelly, which the acetate of lead does not. It answers to the other tests of lead already mentioned.

PLUMBI CARBONAS - CARBONATE OF LEAD - "WHITE LEAD," 2PbCO3PbO,H1O,= 775.

Preparation

No process is given in the Pharmacopoeia, but the carbonate is prepared on a large scale by exposing thin sheets or gratings of lead, placed in earthen pots, to the combined action of acetic acid, air, and carbonic acid gas.

Characters

A heavy white powder, insoluble in water, but readily soluble in dilute acids, with effervescence.

PLUMBI IODIBUM - IODIDE OF LEAD, PbI2,=461.

Preparation

By precipitating a clear solution of nitrate of lead with iodide of potassium, washing, and desiccating.

Characters

A bright yellow powder, darkened by heat, almost insoluble in cold water, soluble in boiling water, from which it is deposited in golden crystalline scales; soluble in solution of acetate of sodium. It fuses and sublimes yellow, but soon gives off violet vapor (Garrod).

PLUMBI NITRAS - NITRATE OF LEAD, Pb(NO3)2,=283.

Preparation

By dissolving lead, or its oxide or carbonate, in boiling nitric acid, slightly diluted, then crystallizing out.

Characters

Octahedral crystals of white waxy appearance, and sweetish, astringent taste, soluble in water and alcohol, not efflorescent.

Absorption And Elimination

Soluble lead compounds, when introduced into the stomach, are transformed probably into chlorides, but in any case are readily absorbed, as shown by clinical results; it is presumed that they circulate mainly as albuminates.

Workers in lead, such as compositors, plumbers, and painters, absorb the metal in part by the skin, in part by the lungs, and sometimes directly with the food (from eating with unwashed hands), and injurious effects are not uncommon from the application of cosmetics and dyes containing lead, to the skin and hair (v. p. 257). Once within the system lead remains for a long time, in small quantities at least, and may be deposited in different organs. It has been found not only in the blood and in the liver, spleen, and kidney, but also in the muscles and bones, and Chatin recovered 3 milligr. of lead sulphide from 150 grammes of the upper cervical cord - the tissue was dark gray in color (Comptes Rendus, Soc. de. Biol., t. iv., 1862). Lead is eliminated chiefly in the form of chloride through the liver, kidneys, skin, and mucous membranes, especially those of the urinary tract; the process is markedly promoted by iodide of potassium.

(It will be seen from the above observations that I cannot accept the conclusions of Mayencon, "that lead is not absorbed by the skin," and that after being taken, "its elimination is prompt and complete" - Medical Times, i., 1873, p. 489).

Physiological Action (External)

Solutions of acetate and nitrate of lead, if not too strong, exert a local astringent and sedative action, coagulating albumen, contracting the vessels, blanching the tissue, and controlling congestion if present; on the other hand, if the solution be too strong, and be applied to a delicate part, such as the conjunctiva, it excites severe irritation. The carbonate of lead, applied in fine powder, is sedative and slightly astringent. The iodide is slightly stimulant and absorbent. The nitrate and chloride decompose sulphuretted hydrogen, combining with the sulphur, and hence they act as deodorants.

Physiological Action (Internal)