Plaster, an external application of a more solid consistence than ointments, and which is usually spread on linen, leather, or tow, according to the nature of the wound or ulcer.

Plasters are prepared chiefly from unctuous matters, which are combined with powders, so as to retain their firmness when cold, without adhering to the fingers; though becoming soft and pliable in a low degree of heat, and acquiring sufficient tenacity from the warmth of the human body, to adhere to the part to which they are applied. The consistence of these compounds varies, according to the different parts of the body, for which they are intended. Thus, if they be designed for the stomach or breast, it will be necessary to make them very soft and plian': one ounce of expressed oil, with a similar quantity of yellow wax, and half an ounce of any suitable powder, will form a convenient plaster. But, if the preparation be required for the limbs, it ought to be made more firm and adhesive : hence, a double portion of wax, and an additional half ounce, of powder, should be properly incorporated, and spread on leather, linen, or tow, in the usual manner.

London court-plaster: Dissolve the best isinglass (previously cut in small pieces) in any proof spirits, so as to obtain a strong viscid solution ; then take taffety, or other thin silk, and spread the liquor uniformly over it, with a soft brush : when the first coat is perfectly dry, repeat this application a second and third lime, till at length the whole surface should be sparingly anointed with Peruvian balsam.—Others prepare this noted plaster, by dissolving equal parts of storax in the cane; benzoin, the resin; and isinglass, in spirits of wine : these ingredients are to be digested in a glass retort, placed in a moderate heat for twenty-four hours 5 when the solution is filtered, and applied while lukewarm, in a manner similar to the preceding, but without any balsam.—See also WaRt and Wound.