QtllCK-LIME. 



.ibout one-tenth of pure hme-ftone is not enough calcined 

 to admit of being made into mortar; and tliat of the 

 mofl impure forts of hme-ftone, not above one-fourth part 

 of the lime contained in it ia fo much calcined as to be in a 

 cauitic ftate. 



The variation that is produced by thefe means ui regard to 

 the proportion of fand that will be required to tiie lime in the 

 one or the other cafe, is found to be fo extremely great as 

 hardly to be conceived. It is, however, ftatcd, that the bell 

 mortar that has been feen made, was formed of lime which 

 had been found to contain eleven parts of fand to one of 

 lime : to this there was added between twice and thrice 

 its whole bulk of fand by meafure ; which may be allowed 

 to have been at leall three times its quantity by weight. 

 Therefore, fuppofing that every particle of that lime had been 

 fo perfeftly calcined as to be in a cauitic ftate, there could not 

 be lefs than forty-feven parts of fand to one of lime. .As 

 much may, however, be allowed for the uncauftic part of 

 the hme as is pleafed, and the calculation made accordingly. 

 But it is hardly poflible to fuppofe that above one-hundredth 

 part of this mafs, independent of the water, confifted of 

 pure cauitic calcareous earth. 



On thefe confiderations it is conceived, that it is impof- 

 fible to prefcribe any determinate proportion of fand to 

 lime, as tliat muft vary according to the nature of the Hme 

 and other incidental circumftances, which would form an 

 infinity of exceptions to any general rule. But it would 

 feem that it might be fafely inferred that the moderns in 

 general rather err in giving too little fand, than in giving too 

 much. It deferves, however, to be noticed, that the land, 

 when naturally in the lime-ftone," is more intimately blended 

 with the lime than can poffibly be ever eff'efted by any 

 mechanical operation ; fo that it would be in vain to hope 

 to make good mortar artificially from pure hme, with fuch 

 a fmall proportion of cauftic calcareous matter as may fome- 

 times be effeited when the lime naturally contains a very 

 large proportion of fand. But there feems to be no doubt, 

 that if a much larger proportion of fand were employed, 

 and if that were more carefully blended and expeditioufly 

 worked than is common, the mortar would be much more 

 perfeft than is ufual in modern times, as has been proved by 

 aftual trials. 



Another circumftance that tends greatly to vary the 

 quality of cement, and to make a greater or fmaller pro- 

 portion of fand neceffary, is the mode of |>reparing lime 

 before it is beaten up into mortar. When for plaifter, it is 

 of great importance to have every particle of tlie lime-ftone 

 flaked before it is worked up ; for, as fmoothnefs of the 

 furface is the uioft material point, if any 'particles of lime 

 fiiould be beaten up in it, and employed in work before 

 fufficiently fallen, the water, ftill continuing to aft on them 

 after it was worked up, would infalhbly flake fuch par- 

 ticles, which forcibly expanding themfelves, would pro- 

 duce thofe excrefcences on the furface of the plaifter com- 

 monly termed bhfters. Confequently, in order to obtain 

 a perfett kind of plaifter that will remain fmooth on the 

 furface and free of blifters, there is an abfolute neceliity 

 to allow the lime to lie for a confiderable time macerating 

 or fcur'mg in water, before it is worked up. And the 

 fame fort of procefs is neceflary for the lime when intended 

 for ufe as mortar, though not fo abfolutely. Great care is, 

 however, required in the management in this refpeft ; the 

 pnncipal things being the getting of well-burnt lime, and 

 the allowing it to macerate or four with the water for only 

 a very Jtmrt time before it is ufed ; but that which is the 

 beft burnt will require the maceration of fome days in 

 the water before it is fufficiently flaked in the whole 



mafs for this purpofe. See SovRiuc Lime for Mortar and 



Plaijkr. 



It has been almoll univerfally admitted, that the hardeft 

 lin.c-ftone affords a lime that will confolidate into the 

 firmell cement ; and hence generally concluded, that lime 

 made of chalk, produces a much weaker cement than what 

 is made of marble or hme-ftone. It would feem, however, 

 that if ever this be the cale, it is only incidentally, and 

 not necefl'arily fo. As from the nature of calcareous mat- 

 ter, every kind of lime is equally fit for becoming a firm 

 cement, if it be firll reduced to a proper degree of cauf- 

 ticity, and has afterwards a due proportion of fand properly 

 mixed with it, before it be employed in work. Difi'erent 

 forts of hme, without doubt, differ much from each other in 

 the proportion of fand they naturally contain, and, of 

 courfe, require very different proportions of fand to be 

 added to them before they can be made equally perfect as a 

 cement ; which is an economical confideration, of no fmall 

 moment in fome cafes, as it may make one fort of lime a 

 great deal cheaper than another on fome occafions, and, of 

 courle, deferves the attention of builders in general. See 

 Lime. 



The excellencies and defefts of other fubftances that may 

 be occafionally mixed with lime in making cement may be 

 juft noticed. Thofe commonly ufed as an addition to mor- 

 tar, befides fand of various denominations, are powdered 

 fand-ltone, brick-dult, and fea-fheUs. And for forming 

 plaifter, where clofencfs rather than iiardnefs is required, 

 they are hme that has been flaked and kept long in a dry 

 place, till it has become nearly effete, powdered chalk or 

 whiting, and gypfum in various proportions ; befides hair 

 and other materials of that nature. But fome others have 

 been more lately advifed, fuch as earthy balls, flightly burnt 

 and pounded, powdered and fifted old mortar rubbifh, and 

 others of a fimilar kind. All of which fubftances are 

 found objeftionable in fome refpeft or other for this ufe, 

 fand being the only perfedtly fuitable material that can be 

 eaflly met with ; on which account it has been always juftly 

 preferred. Pure firm cryitaUized fand is the beft, but all 

 pure fands are flot equally proper in this intention. See 

 thefe fubftances refpectively. See alfo Cement and S.'VND. 

 It is dated by fir Humphry Davy, in his work on " Agri- 

 cultural Cheraiftry," that there are two modes in which lime 

 afts as a cement ; in its combination with water, and in its 

 combination with carbonic acid. When quick-lime is rapidly 

 made into a pafte with water, it foon lofes its foftnefs, and 

 the water and the lime form together a folid coherent mafs, 

 which confills of feventeen parts of water, to fifty-five 

 parts of hme. When this hydrate of lime, while it is con- 

 folidating, is mixed mth red oxyd of iron, alumina, or fihca, 

 the mixture becomes harder and more coherent than when 

 lime alone is ufed ; and it appears that this is owing to a cer- 

 tain degree of chemical attradion between hydrate of hme 

 and thefe bodies ; and they render it lefs hable to decompofe 

 by the adlion of the carbonic acid in the air, and lefs folu- 

 ble in water. It is thought that the bafis of all cements that 

 are ufed for works which are to be covered with water muft 

 be formed from hydrate of Hme ; and that the lime made 

 fromimpure lime-ftones anfwers this purpofe very well. Puz- 

 zolana, it is faid, is compofed principally of fihca, alumina, 

 and oxyd of iron ; and it is ufed mixed with lime, to form 

 cements intended to be employed underwater. It is itated 

 that Mr. Smeaton, in the conftrudlion of the Eddyftone 

 lighthoufe, ufed a cement compofed of equal parts, by 

 weight, of flaked lime and puzzolana. Puzzolana, it is 

 faid, is a decompofed lava. Tarras, which was formerly 

 imported in confiderable quantities from Holland, is found 



to 



