Plaster, Kennedy’s. See Plasters, Corn.
Plaster, Kirkland’s. See Plaster, Ammoniacal.
Plaster of Lab′danum. See Plaster, Cephalic.
Plaster of Lead. Syn. Lead plaster, Litharge p., Common p., Diachylon, Simple diachylon, White d.; Emplastrum plumbi (B. P., Ph. L.), E. lythargyri (Ph. E. & D.), E. commune, Diachylon simplex, L. Prep. 1. (Ph. L.) Oxide of lead (litharge), in very fine powder, 6 lbs.; olive oil, 1 gall.; water, 1 quart; boil them over a slow fire, constantly stirring to the consistence of a plaster, adding a little boiling water, if nearly the whole of that used in the beginning should be consumed before the end of the process.
2. (Ph. E.) Litharge, 5 oz.; olive oil, 12 fl. oz.; water, 8 fl. oz.; as the last.
3. (Ph. D.) Litharge, 5 lbs.; olive oil, 1 gall.; water, 1 quart.
4. (Otto Kohnke.) For each lb. of litharge employed, add 1⁄4 pint of colourless vinegar (each fl. oz. of which is capable of saturating 1⁄2 dr. of carbonate of potassa); add the oil, boil until all moisture is evaporated, and until only a few striæ of litharge rise to the surface, then remove the vessel from the heat, add gradually 1⁄3 to 1⁄2 as much vinegar as before, and boil the mixture to a proper consistence.
5. (Wholesale.) From Genoa oil, 7 galls. (or 65 lbs.); litharge (perfectly free from copper), 28 lbs.; water, 21⁄2 galls.; boil to a plaster, as before.
6. (B. P.) Oxide of lead, in very fine powder, 1; olive oil, 21⁄2; water, 1; boil all the ingredients together gently by the heat of a steam bath, and keep them simmering for 4 or 5 hours, stirring constantly until the product acquires the proper consistence for plaster, adding more water during the process, if necessary.
Obs. The London College orders too little oil. The second, fourth, and fifth formulæ produce beautiful plasters, that keep well; those of the others, although very white, get hard and brittle much more rapidly. The proper proportion of oil is fully 21⁄3 times the weight of the litharge,—21⁄2 times appears the best quantity; and without this is used, the plaster speedily gets hard and non-adhesive. The process consists in putting the water and the litharge into a perfectly clean and well-polished tinned copper or copper-pan, mixing them well together with a spatula, adding the oil, and boiling, with constant stirring, until the plaster is sufficiently hard, when thoroughly cold. This process usually occupies from 4 to 5 hours, but by adopting the fourth formula an excellent plaster may be made in from 20 to 30 minutes. This plaster is generally cooled by immersion in cold water; and to render it very white, a quality highly prized in the trade, it is usual to submit it to laborious ‘pulling,’ in the manner already noticed.