520

ELEMENTS OF MATERIA MEDICA.

Goulard water is used as a cooling, sedative, and astringent washin the cases already enumerated for the Goulard’s extract. A poultice,composed of crumb of bread, boiled in Goulard water, is sometimes avery useful application to phlegmons, painful wounds, irritable ulcers,&c. &c.

Ceratum Plumri Compositum, Ph . Lond. (Solution of diacetateof lead, fSiij.; wax, 5iv.; olive oil, Oss.; camphor, 5ss. M.).—This is thecerate of Saturn of M. Goulard, and is commonly called Goulard’scerate. It is employed as a dressing to wounds and ulcers, for the pur-pose of allaying irritation and appeasing pain, With the same views itis also applied to excoriated surfaces, burns, scalds, blistered surfaces,and irritable cutaneous affections. Opium is sometimes advantageouslycombined with it.

Ceratum Saponis, Ph . Lond.—This contains a subacetate of lead.It has been before described (p. 337).

Emplas'trum Plum!bi.—Plas'ter of Lead .

History. —This compound was known to the ancients: both Pliny (Hist. Nat. xxxiv. 53) and Celsus (He Medicina, lib. v. cap. xix.) give aformula for a plaster used by the Roman surgeons, which is almost iden-tical with that for the officinal plaster of lead.

It is termed emplastrum lythargyri in the Dublin Pharmacopoeia, andis commonly sold in the shops as diachylon or diachylum.

Preparation. —In the London Pharmacopoeia it is directed to beprepared by mixing six pounds of oxide of lead (litharge), rubbed to avery fine powder; a gallon of olive oil; and two pints (3x1.) of water.These are to be boiled together over a slow fire, constantly stirring, to aproper consistence.

In this process the oil becomes saponified, and converted, by the aidof the elements of water, into glycerine , oleic acid, and margaric acid.The glycerine remains in solution in the water, while the two fatty acidscombine with the oxide of lead to form the oleo-margarate of lead orplaster of lead.—(For further particulars respecting the theory of saponi-fication, vide p. 334).

The water used in this process serves two purposes; it moderates theheat, and facilitates the union of the acids with the oxide of lead.

Properties.— It is met with in the shops in cylindrical rolls, of agreyish or yellowish-white colour, brittle when cold, but softening andultimately fusing by heat. It is insoluble in water, and nearly so inalcohol. It lias no taste, but a slight though peculiar odour.

Characteristics. —When heated it fuses, then decomposes, gives outinflammable gas, and leaves a carbonaceous residue, which, when heatedin a close vessel, yields globules of lead. Ether dissolves the oleatebut not the margarate of lead.

Composition.— Berzelius ( Traite de Chim. v. 373) says this compoundis to be regarded as a tribasic salt: that is, as consisting of one equiva-lent of the fatty acids (oleic and margaric) and three of the oxide oflead.

Effects and Uses. — This plaster is employed in surgery, on accountof its adhesiveness and the mildness of its local action ; for it rarelyexcites irritation. It is used to keep the edges of wounds together inpersons with delicate skins. Spread on calico it forms a good strap-