sou 



per for tliefe ufes. It lias been ftated by the writer of an 

 " Eflay on Quicklime as a Cement," that when lime is to 

 be employed for making plaller, it is of great importance 

 that every particle of the limeftone be flaked before it is 

 worked up ; for, as the fmoothnefs of the furface is the 

 circumltance moft wiflied for in plaller, if any particles of 

 lime fliould be beaten up in it, and employed in work be- 

 fore they have had fufficicnt time to fall, the water Hill con- 

 tinuing to aft upon them after the materials have been 

 worked up, will infallibly flake fuch particles, which will 

 then expand themfelves in a forcible manner, and be pro- 

 duAive of thofe excrefcences upon the furface of the 

 plaiter, which are commonly known by the name of bliflers. 

 Confequently, if it be intended to have a perfeft kind of 

 plaiter, which is capable of remaining fmooth on the furface 

 and free from bliilers, there is an abfolute neceflity for 

 allowing the lime of wliich it is compofed, to lie for a con- 

 liderable length of time in maceration with water, before 

 it is wrought up into plaller, which is a procefs or opera- 

 tion that is here termed fouring. Where the limeltone 

 is of a pure quahty, and has been very perfeftly calcined 

 or burnt, there will feldom be any danger of the whole of 

 the lime falling at firit ; but where it has been lefs per- 

 feftly burnt, there will be many particles, which will re- 

 quire to lie a long time before they will be completely re- 

 duced into powder. This macerating procefs or operation 

 is confequently more nccefiary with impure than pure lime; 

 but lUU it ought on no occafion to be omitted or neglefted, 

 as there is not the fmallelt probability, but that fome 

 blifters would appear on the farfacc of plallers made with 

 even the purell lime, when worked up and applied imme- 

 diately after being flaked, without undergoing this fouring 

 procefs in fome degree. 



The praftice is alfo common of fouring the lime when 

 it is intended for being ufed in mortar ; but although it is 

 uot fo indifpenlably nccefiary in this cafe, as in that where 

 it is defigned for plafter, yet, when properly performed, 

 it is evident, it is faid, that it muft even in this inltancc too 

 be of utility ; as any dry knots of lime that may fall after 

 the mortar is ufed, muft have a tendency to difunite the 

 parts of it, which have already been united, and to render 

 the mortar or cement much lefs perfeft than if the whole 

 had been properly mixed up with the materials and allowed 

 to four before uling. More circumfpcftion is, however, 

 requifite, it is faid, in fouring lime for mortar than for 

 plafter ; for, as it is not neccHary that plafter ftiould be en- 

 dowed with a ftony degree of hardnefs, there is no lofs 

 fuftained by allowing a great proportion of the lime which 

 is defigned for that purpofe to abforb its air before it be 

 ufed ; for a very fmall quantity of cauftic or quicklime 

 will be lufficicnt to unite the whole into one flightly co- 

 herent mafs. Confequently, the only circumftance which 

 is neceflary to be attended to in fouring lime for plafter is, 

 that it be allowed to macerate long enough, as there is no 

 danger of ever erring on the oppolite extreme. It is in- 

 deed necell'ary, it is faid, on fome occafions, it fliould lie 

 a very long time, before any certainty can be had, that all 

 the particles are thoroughly flaked, as pieces of lime-fhells 

 have been known to he upwards of fix months expoled to 

 all the changes of the winter weather, and fall alter that 

 psriod. Such flightly burnt Itoiies are indeed, it is faid, 

 ufually fcparated in fifting the lime for plafter ; but as fome 

 fmall chips may efcape, it is always the fafelt way to allow 

 lime to lie in the four a very confidcrable length of time. 

 Another advantage of fome confequence likewile, it is laid, 

 attends this praftice ; as, if by fuch means a large propor- 

 tion of the lime be allowed to abforb its air, and become 



Vol. XXXIII 



SOU 



in the mild or effete ftate, when it is wrought or beaten up 

 for ufe, the water can have no fenfible effeft upon this mild 

 lime ; it will only fcparate the particles of the cauftic lime 

 more perfeftly from each other, fo as to permit it to dry 

 without cracks of any kind, and render the furface of the 

 plaiter a great deal more fmooth and entire, than could 

 have been the cafe, if the whole had been made ufe of 

 while in the perfeftly cauftic ftate. By this means too, 

 thofe cryftalline exudations, which are fo common on walls 

 newly plaflered, will be the belt and moft effeftually pre- 

 vented. On all which accounts, the praftice of fuft'cring 

 lime, which is defigned for plafter, to macerate or iour a 

 long time with water, fliould never, it is faid, except in 

 cafes of neceihty, be neglefted or overlooked. 



However, as hme, from the moment of its being fully 

 flaked, begins to abforb air, and continues to take up more 

 and more every minute from that time until it becomes 

 perfeftly mild or effete, fo as to be rendered gradually lefs 

 and lefs proper for forming mortar of any kind, it necef- 

 farily follows, that where lime defigned for this purpofe is 

 permitted to lie long in the four, a great part of it will be 

 converted into chalky matter, or uncryftallized mild or 

 effete lime, in which ftate it will be capable of having fo 

 much fand added to it, or of forming fo good a mortar as 

 would have been the cafe, if a larger proportion of the 

 fandy material had been made ufe of in the firIt place, and 

 been wrought up as fpeedily as poffible, without lo much 

 fouring, into mortar, and immediately made ufe of. The 

 evil will alfo be increafed where the lime has been but 

 flightly burnt, confequently the bell burned lime fl\ould 

 always be preferred for this ufe, which, when carefully 

 fifted after flaking, will foon fall fufficiently for this pur- 

 pofe ; as the main point here is to have the mortar firm and 

 binding ; and the falling or burlting of very fmall unflaked 

 particles of lime in the mortar afterwards, will not be pro- 

 duftive of fuch evident inconvenience as is the cafe in the 

 making and ufing of plafter. In the making of good 

 mortar, it will confequently be neceffary to get the bell 

 burnt lime, and to only fufter it to macerate or four with 

 water a very fhort time before it is wrought and applied. 

 The bell burnt lime, however, moftly requires fome days 

 to macerate and four with water, be-fore the whole be- 

 comes fully flaked and fallen for this ufe. 



This doftrine of the nature and utility of the fouring 

 procefs in the making of tliefe fubftances is fuppofed to re- 

 ceive additional proof and fupport from the praftice which 

 was followed by the ancients, which is very fimilar to this, 

 if the accounts given of it by Vitruvius and Pliny can be 

 depended on. The former, it is faid, cxprcfsly recom- 

 mends that the lime fhould be macerated or fourcd in water, 

 for exaftly the fame reafons that have been already feen, 

 as it is only by that means, he allerts, that the plafter can 

 be prevented from bliftering. His words are tliefe : " tunc 

 de albariis operibus ell cxplicaiidum. Id autem crit reflc, 

 fi gleb'JE calcis optime, ante multo tempore quam opus 

 fuerit, macerabuntur. Niimque cum non penitus macerata, 



fed recens fiimitur hahtns lalenles crudot cuculos, puflulat 



om'Ut'il. (2»( calculi diffolvunt el dijfipani leSorii pelitionet." 



Vit. lib. vii. c. 2. 



The latter points out, it is faid, in a ftill more clear 

 maimer, the difference between the quality of the lime, 

 which is neceffary for making mortar and plafter: — a cer- 

 tain proof, it is conceived, that the ancients had been very 

 accurate in the obfcrving of fafts, as they could hive no 

 idea of the reafoiiing by which thofe fafts might have been 

 corroborated or explained. 



" Kuiiiarum urbis," fays he, " ea maxime caufa, quod 

 3 E furto, 



