pulled or worked until it becomes solid enough to admit of being formed into rolls. To promote the cooling of the plaster it is usual to plunge it into cold water, and to expose it to the action of the fluid by working it about under the surface, after which it is well pulled in the hands to remove the superfluous water; but this process must not, on any account, be practised on compound plasters, containing odorous substances, or substances soluble in water. These should be suffered to cool on an oiled marbled slab, until sufficiently ‘stiff’ to be formed into rolls. Many plasters, as those of lead and resin, derive much of their whiteness and beauty from the treatment just referred to. White plasters are not, however, always the best; but they are those which are most admired, and the most sought after in trade.
Plasters are preserved by enveloping the rolls with paper, to exclude the air as much as possible, and by keeping them in a cool situation. A few, as those of belladonna and ammoniacum with mercury, are commonly placed in pots. When kept for any length of time, they are all more or less apt to become hard and brittle, and to lose their colour. When this is the case, they should be remelted by a gentle heat, and sufficient oil added to the mass to restore it to a proper consistence.
The operation of spreading plasters for use requires skill and experience on the part of the operator. Various textures are employed for the purpose, of which linen or cotton cloth, or leather, are those most generally employed. Silk and satin are used for ‘court plaster.’ The shape and size must be regulated by the part to which they are to be applied.
On the large scale plasters are spread by means of a ‘spreading machine.’
Compound plasters are now much less frequently employed in medicine than formerly. Those principally in use are such as afford protection to sores and abraded surfaces, and give support to the parts. A few, however, which contain acrid, stimulating, and narcotic substances, and operate as rubefacients, blisters, or anodynes, are still retained in the Pharmacopœias.
Plaster of Ac′onite. Syn. Emplastrum aconiti, L. Prep. (Curtis.) Gently evaporate tincture of aconite to the consistence of a soft extract, then spread a very small portion over the surface of a common adhesive plaster, on either calico or leather. Mr Curtis has strongly recommended this plaster in neuralgia. A little of the alcoholic extract may be employed instead of that obtained fresh from the tincture.
Plaster, Adhe′′rent. See Plaster, Soap (Compound).
Plaster, Adhe′sive. See Plaster, Resin, Court p., &c.
Plaster, Adhesive Lime. Syn. Emplastrum adhæsivum calcareum.
Prep. Soap of lime, 200 parts; boiled turpentine, 100 parts; suet, 25 parts.