if, by this means, a great proportion of the lime be allowed to abforb its air, and become effete, when it is beat up for use, the water can have no fenible eff t upon that effete-lime—it will only separate the particles of cauftic-line more perfectly from one another, fo as to fuffer it to dry without cracks of any fort, and render the furface of the plafter much more smooth and entire than it could have been, if the whole had been employed while in its perfectly cauftic ftate. By this means alfo those chryftalline exudations, fo common on newly plastered walls, will be moft effectually obviated. On all which accounts, the practice of allowing lime intended for plafter to macerate very long with water ought never to be omitted, but in cafes of neceffity.

But, as lime is no fooner flaked than it begins to absorb its air,—and as it continues Y y

to

to absorb more and more every minute from that period, till it becomes entirely effete ; fo as to be rendered gradually lefs and lefs fit for forming a cement of any fort;-it follows, that if lime intended for mortar is allowed to lie long in the four, much of it will be converted into chalk, or unchrystallized effete-lime-in which condition it will neither admit of fo much fand in ufing, nor ever become fuch a firm cement, as if a larger proportion of fand had been employed at first, and worked up as quickly as poffible into mortar, and used.

This malady will be encreafed, if the lime-ftone has not been very well burnt; therefore care ought to be taken to chufe the very beft burnt lime for mortar; in which cafe a very fhort time, if it has been carefully fifted after flaking, will be fufficient to make it fail as much as is necessary. For the object of principal importance here is, to have the cement as firm as poffible;

and

and the bursting of a very fmall particle of unflaked lime amongst it afterwards, will not produce fuch a fenfible inconvenience as it would have done in plafter.

Thofe, therefore, who wish to obtain the hardest and firmeft mortar, will be. careful to get well burnt lime, and allow it to macerate with the water only a very short time before it is used. But the best burnt lime I ever faw would require to macerate fome days in the water before there can be a certainty that the whole will be fufficiently flaked*.

$ 28,

It is no unfatisfactory proof of the juftnefs of the foregoing reasoning to observe, that the practice which would neceffarily follow from it is exactly what was followed by the antients, if we can rely on the account given of this matter by Vitruvius and Pliny.

Vitruvius, fo far from recommending unflaked lime for making plafter, as Monfieur Loriot would fuggeft, recommends exprefsly that it fhould be foured or macerated in water-for the very fame

reafons

$ 28.

The reader, if he has followed me thus far, will cafily perceive, that, although it be

in

reafons as are given above; as it is only by that means, he fays, that the plafter can be prevented from bliftering His words are, (Lib. vii. cap. 2.) "Tunc de albariis operibus eft explicandum. Id autem erit recte, fi glebae calcis optime, ante multo tempore quàm opus fuerit, macerabunNamque cum non penitus macerata, fed recens habens latentes crudos calculos, pu

fumitur ftulas emittit

pant teorii politiones."

Pliny points out ftill more clearly the difference between the quality of the lime neceflary for making mortar and plafter a certain proof that the antients had been very accurate in obierving facts, as they could have no idea of the reasoning by which these facts might have been explained or corroborated.

"Ruinarum urbis," fays he, "ea maximè caufa, quod furto, calcis fine ferrumine fuo caementa componuntur.

in vain to expect thofe wonderful effects from the practice recommended by Monfieur Loriot,

ponuntur. Intrita quoque quò vetuftior, eò melior. In antiquarum (antiquis) aedium legibus invenitur, ne recentiore trima uteretur redemptor; ideo nulla (nullae) tectoria eorum rimae foedavere;" Plin. Hift. Lib. xxxvi cap. 23.

In this paffage Pliny ftrongly contrafts mortar (caementa) with plaster (intrita). The first, he fays, (by implication), ought always to be compofed of lime cum ferrumine fuo, that is, lime that still retains its gluten,-lime that still retains that quality by which it is enabled to unite into a solid body, and glue them, as it were, together. In other places of his work he defcribes it as calcis quam vehementiffimae, lime in its moft acrid ftate, that is, perfectly caustic lime.

This quality, he plainly hints, it gradually lofes by time, fo as to come at length to be fine ferrumine fuo; in which state, as it is impoffible to become a firm cement for building, he feverely reprehends those who use it as fuch.

But, although he condemns the practice of ufing that old and inert lime for mortar, he immediately

adds,