PLASTERS.
Plasters ought to be of a different consistence, according to the purposes for which they are intended. Such as are to be applied to the breasts or stomach ought to be soft and yielding; while those designed for the limbs should be firm and adhesive.
It has been supposed, that plasters might be impregnated with the virtues of different vegetables, by boiling the recent vegetable with the oil employed for the composition of the plaster; but this treatment does not communicate to the oils any valuable qualities.
The calces of lead boiled with oils unite with them into a plaster of a proper consistence, which make the basis of several other plasters. In boiling these compositions, a quantity of hot water must be added from time to time to prevent the plaster from burning or growing black. This, however, should be done with care, lest it cause the matter to explode.
Common Plaster.
Take of common olive oil, six pints; litharge reduced to a fine powder, two pounds and a half. Boil the litharge and oil together over a gentle fire, continually stirring them, and keeping always about half a gallon of water in the vessel: after they have boiled about three hours, a little of the plaster may be taken out and put into cold water, to try if it be of a proper consistence: when that is the case, the whole may be suffered to cool, and the water well pressed out of it with the hands.
This plaster is generally applied in slight wounds and excoriations of the skin. It keeps the part soft and warm, and defends it from the air, which is all that is necessary in such cases. Its principal use, however, is to serve as a basis for other plasters.
Adhesive Plaster.
Take of common plaster, half a pound; of Burgundy pitch, a quarter of a pound. Melt them together.
This plaster is principally used for keeping on other dressings.