or EMLASTER, in Pharmacy, an external application of a harder consistence than an ointment; to be spread, according to the different circumstances of the wound, place, or patient, either upon linen or leather.

or Plaster, in building, a composition of lime, sometimes with sand, &c. to parget, or cover the nudities of a building. See PARGETING and STUCCO.

PLASTER of Paris, a preparation of several species of gypsum dug near Mount Martre, a village in the neighbourhood of Paris; whence the name. See ALABASTER, GYPSUM, and SULPHATE OF LIME, under CHEMISTRY.

The best sort is hard, white, shining, and marbled; known by the name of plaster-stone or parget of Mount Martre. It will neither give fire with steel, nor ferment with aquafortis; but very freely and readily calcines in the fire into a fine plaster, the use of which in building and casting statues is well known.

The method of representing a face truly in plaster of Paris is this: The person, whose figure is designed, is laid on his back, with any convenient thing to keep off the hair. Into each nostril is conveyed a conical piece of stiff paper, open at both ends, to allow of respiration. These tubes being anointed with oil, are supported by the hand of an afflatus; then the face is lightly oiled over, and the eyes being kept shut, alabaster fresh calcined, and tempered to a thinness consistence with water, is by spoonfuls nimbly thrown all over the face, till it lies near the thickness of an inch. This matter grows sensibly hot, and in about a quarter of an hour hardens into a kind of stony concretion; which being gently taken off, represents, on its concave surface, the minutest part of the original face. In this a head of good clay may be moulded, and therein the eyes are to be opened, and other necessary amendments made. This second face being anointed with oil, a second mould of calcined alabaster is made, consisting of two parts joined lengthwise. lengthwise along the ridge of the nose; and herein may be cast, with the same matter, a face extremely like the original.

If finely powdered alabaster, or plaster of Paris, be put into a basin over a fire, it will, when hot, assume the appearance of a fluid, by rolling in waves, yielding to the touch, foaming, &c., all which properties it again loses on the departure of the heat; and being thrown upon paper, will not at all wet it, but immediately discover itself to be as motionless as before it was set over the fire; whereby it appears, that a heap of such little bodies, as are neither spherical nor otherwise regularly shaped, nor small enough to be below the discernment of the eye, may, without fusion, be made fluid, barely by a sufficiently strong and various agitation of the particles which compose it; and moreover lose its fluidity immediately upon the cessation thereof.

Two or three spoonfuls of burnt alabaster, mixed up thin with water, in a short time coagulate, at the bottom of a vessel full of water, into a hard lump, notwithstanding the water that surrounded it. Artificers observe, that the coagulating property of burnt alabaster will be very much impaired or lost, if the powder be kept too long, especially if in the open air, before it is made use of; and when it hath been once tempered with water, and suffered to grow hard, they cannot, by any burning or powdering of it again, make it serviceable for their purpose as before.

This matter, when wrought into veils, &c., is still of so loose and spongy a texture, that the air has easy passage through it. Mr. Boyle gives an account, among his experiments with the air-pump, of his preparing a tube of this plaster, closed at one end and open at the other; and on applying the open end to the cement, as is usually done with the receivers, it was found utterly impossible to exhaust all the air out of it; for fresh air from without pressed in as fast as the other, or internal air, was exhausted, though the sides of the tube were of considerable thickness. A tube of iron was then put on the engine; so that being filled with water, the tube of plaster of Paris was covered with it; and on using the pump, it was immediately seen, that the water palled through into it as easily as the air had done, when that was the ambient fluid. After this, trying it with Venice turpentine instead of water, the thing succeeded very well; and the tube might be perfectly exhausted, and would remain in that state several hours. After this, on pouring some hot oil upon the turpentine, the case was much altered; for the turpentine melting with this, that became a thinner fluid, and in this state capable of palling like water into the pores of the plaster. On taking away the tube after this, it was remarkable that the turpentine, which had pervaded and filled its pores, rendered it transparent, in the manner that water gives transparency to that singular stone called oculus mundi. In this manner, the weight of air, under proper management, will be capable of making several forts of glues penetrate plaster of Paris; and not only this, but baked earth, wood, and all other bodies, porous enough to admit water on this occasion.

Plaster of Paris is used as a manure in Pennsylvania, as we find mentioned in a letter from a gentleman in that country inserted in the fifth volume of the Bath Society Papers, and which we shall insert here for the satisfaction and information of our agricultural readers. "The best kind is imported from hills in the vicinity of Paris; it is brought down the Seine, and exported from Havre de Grace. I am informed there are large beds of it in the bay of Fundy, some of which I have seen nearly as good as that from France; nevertheless several cargoes brought from thence to Philadelphia have been used without effect. It is probable this was taken from the top of the ground, and by the influence of the sun and atmosphere deprived of the qualities necessary for the purposes of vegetation. The lumps composed of flat shining specks are preferred to those which are formed of round particles like sand; the simple method of finding out the quality is to pulverize some, and put it dry into an iron pot over the fire, when that which is good will loom boil, and great quantities of the fixed air escape by ebullition. It is pulverized by first putting it in a flambing-mill. The finer its pulverization the better, as it will thereby be more generally diffused.

"It is best to sow it in a wet day. The most approved quantity for grass is six bushels per acre. No art is required in sowing it more than making the distribution as equal as possible on theeward of grass. It operates altogether as a top manure, and therefore should not be put on in the spring until the principal frosts are over and vegetation hath begun. The general time for sowing with us is in April, May, June, July, August, and even as late as September. Its effects will generally appear in ten or fifteen days; after which the growth of the grass will be so great as to produce a large burden at the end of six weeks after sowing.

"It must be sown on dry land, not subject to be overflowed. I have sown it on sand, loam, and clay, and it is difficult to say on which it has been answered, although the effect is sooner visible on sand. It has been used as a manure in this state for upwards of twelve years. Its duration may, from the best information I can collect, be estimated from seven to twelve years; for, like other manure, its continuance very much depends on the nature of the soil on which it is placed.

"One of my neighbours sowed some of his grasses on a field five years ago, another four years ago; a great part of my own farm was sown in May 1788. We regularly mow two crops, and pasture in autumn; no appearance of failure, the present crop being full as good as any preceding. I have this season mowed fifty acres of red clover, timothy grass, white clover, &c., which was plastered last May, July, and September; many who saw the grass eliminated the produce at two tons per acre, but I calculate the two crops at three tons. Several strips were left in the different fields without plaster; these were in a measure unproductive, being scarcely worth mowing. In April 1788, I covered a piece of grass land upwards of two inches thick with barn manure; in the same worn-out field I sowed plaster, to contrast it with the dung. I mowed the dugged and plastered land twice last year and once this; in every crop the plaster has produced the most. You will remember, in all experiments with clover, to mix about one-third timothy grass seed; it is of great advantage in serving as a support for the clover; it very much facilitates the curing of clover, and when cured is a superior fodder. The plaster operates equally as well on the other grasses as on clover. Its effect is said to be good on wheat, if sown in the spring; but I cannot say this from experience. On Indian corn I know its operation..." to be great; we use it at the rate of a table spoonful for a hill, put in immediately after dressing.

"From some accurate experiments last year made and reported to our Agricultural Society, it appears that nine bushels of additional corn per acre were produced by this method of using plaster."