Plasters are mixtures of various fatty or resinous solids of such high melting-point as to be friable when cold, but rendered adhesive by the warmth of the body.

The vehicles of plasters are: Lead plaster; resinous substances, made adhesive by admixture with the medicinal ingredients; and simple plasters, such as isinglass.

The making of plasters does not differ materially from the process employed for ointments and cerates, since they are all prepared by melting the various substances and incorporating the medicinal substances last. The spreading of plasters, though usually done on a large scale, may be easily effected by the pharmacist with the use of a plaster iron.

The official Plasters may be divided into: (1) Lead Plasters; (2) Pitch and Gum-Resin Plasters; and (3) Isinglass Plasters.

(1) The most important plasters are made from Lead Plaster, or Lead Plaster mixed with Resin, the official Resin Plaster.

Percentage or Emplastrum - parts in 100.

Adhaesivum . . rubber 2; petrolatum 2; lead plaster

96

Plumbi (Diachylon) . . . soap 100; lead acetate 60;

water q. s.

From these the following are prepared:

Emplastrum -

Belladonnae...........................ext. belladonna leaves

30

adhesive plaster

70

Capsici...........................adhesive plaster, 15x15 cm.;

oleoresin capsicum

0.25

Hydrargyri . . hydrous wool-fat 10; lead plaster 59;

mercury oleate 1; mercury

30

Opii ............ adhesive plaster 90; water; ext. opium

6

Saponis........................................lead plaster 90; soap

10