QUICK-LIME. 



tar, when as dry as it can be made, and in itsliigheft degree 

 of pcrfedion, will alu'ays be foft, and calily crumbled 

 into powder. 



But that, if, inftead of forming the mortar ot pure lime 

 alone, a large proportion of fand be added to it, the water 

 will in this cafe did'olve as much of the lime as in the 

 former ; and the particles of hard fand, like fticks or threads, 

 when making fugar-candy or other cryftals, while fur- 

 rounded by the watery folution, will help to forward the 

 cryftallization, and render it more perfcft than it other- 

 wife would have been, fo as firmly to rement tlie particles 

 of fand to one another. And as the granules of fand arc 

 perfeftly hard cf themfclves, fo as not to admit of being 

 broken down like the particles of chalk, it neceffarily fol- 

 lows, that the cement made of thcfe materials muil be 

 much more perfeft in every rcfpeft than the former. 



After coiifidering a variety of circumftances in regard to 

 the folubility of lime in water, and its cryilallization, it is 

 remarked, that when a large quantity of fand is mixed in 

 the mortar, that fand will of courfe bear a great proportion 

 to the whole mafs ; fo that the water that may be mixed with 

 the mortar will be much greater in proportion to the quan- 

 tity of lime contained in this mortar, than if the whole had 

 confifted of pure calcareous matter. And that, as the fand 

 abforbs none of that water, — that water, now pure, is at 

 liberty to aft once more upon thofe few particles of cauitic 

 lime that may ftill remain in the mortar, which will be dif- 

 folved and converted into cr\-llals in their turn. In this 

 way it may happen, in fome circumftances, that a very 

 large proportion of the lime may become cryllaUized ; fo 

 that the mortar will confift almoll entirely of fand enve- 

 loped in cryftaUine matter, and become in due time as 

 hard as ftone itfelf; whereas mortar, confifting of pure 

 lime, without fand, can hardly ever be much harder than 

 chalk. It is not, however, to be fnppofed, that in any 

 cafe this dried mortar will all'ume that tranfparent cryf- 

 taUine form, or the compaft hrmnefs of fome forts of cal- 

 careous matters, fuch as marble and hme-itone. In mortar, 

 m fpite of the utmoll care that can ever be taken, a very 

 conliderable quantity of tlie lime muft remain undiflblved ; 

 which undifTolved lime, although it may be fo much fepa- 

 rated by the fand and cryftalline lime-ftone as not much 

 to affeft the hardnefs of the mortar, yet it muft ftill retain its 

 white chalk-like appearance. As marble and lime-ftone are, 

 however, always formed by thofe particles of lime that have 

 been wholly diflTolved in water, and from which they have 

 been gradually feparated by a more flow and more perfeft 

 mode of cryttaUization, they have nothing of that opaque 

 calx-like appearance, but afl'ume other colours, and appear 

 more firm, uniform, and compaft ; the fand and other 

 matters that may be enveloped in them being entirely fur- 

 rounded with a pure cryftalline matter. 



But to obtain the moft perfeft kind of mortar, it is 

 not, however, enough that a large proportion of fand 

 fhould be employed, and that the fand (hould be inti- 

 mately mixed with the lime ; it is alfo of the utmoll im- 

 portance that a large proportion of water be added ; for 

 without this it is impoflible that a large proportion of the 

 lime can be cryllallized : and the mortar, in that cafe, 

 would confift only of a mixture of chalky matter and fand, 

 which could hardly be made to unite at all, and would be 

 little more coherent than fand by itfelf, and lefs fo than pure 

 chalk. In that cafe, pure lime alone muft afford rather a 

 firmer cement than lime with fand. It is alfo of very great 

 importance that the water be retained as long in the mortar 

 ae pofTible : for if it be fuddenly evaporated, it will not only 

 be prevented from afting a fecond tim.e upon the lime, after 



a part of what was firfl difTolved has been cryftallized, 

 but even the few cryftals that would be formed when thir 

 water was fuddenly evaporating, would be of themfelves 

 much more imperfeft than they otherwife moft certainly 

 would have been. In proof of which, inftances of the 

 cryftallization of common fait, lump fugar, and fugar- 

 candy, are adduced ; after which it is noticed, that every one 

 knows what a difference there is between the firmnefs of the 

 different fubilances ; and that as great muft be the difference 

 between tlie firmnefs of that cement which has been flowly 

 dried, and that whicli has been liaflily hardened by the 

 powerful aftion of a warm air. 



It is contended, that it is owing to this circumftance that 

 the lime, which remains all winter in a mortar tub filled with 

 water, is always found to be mucli firmer and more coherent 

 than the mortar that was taken from the fame tub and ufed 

 ill any work of mafonry, althougli in this cafe the materials 

 were exaftly the fame. From the fame caufe, miy work 

 cemented with lime under water, if it has been allowed to 

 remain undifturbed and uninjured until it has once become 

 hard, is always much firmer than that which is above the 

 furface of the water. 



In order to render the force of the above reafoning more 

 ftrong and convincing, lime cement or mortar is compared 

 to a mafs of matter confifting of a congeries of ftones 

 clofely compafted together, and united by a ftrong cement- 

 ing matter that had, while in a fluid ftate, pervaded all the 

 interftices between the ftones, and afterwards become a 

 folid indiffoluble fubilance. If the cementing matter be 

 exceedingly hard and coherent, and if the ftones bedded 

 among it be alfo very hard and firm, the whole mafs will 

 become like a folid rock, without fiflures, that can hardly 

 be broken to pieces by the power of man. But, althougli 

 the cement fhould be equally firm, if the Itone, of which it 

 confifts, be of a foft and triable nature, fuppofe chalk or 

 fand-ftone, the whole mafs will never be capable of attaining 

 fuch a degree of firmnefs as in the former cafe ; for when 

 any force is applied to break it in pieces, although the 

 cement fhould keep its hold, the folid matter cemented by 

 it would give way, and the whole would be eafily broken 

 to pieces. Whereas in mortar, the fand that is added to 

 it reprefents the ftones of a folid matter in the compofition, 

 the particles of which are united together by the lime which 

 had been formerly difTolved, and now cryftallized, which 

 becomes an exceedingly fobd and indilloluble concretion. 

 And as the particles of fand are of themfelves exceedingly 

 hard, and the cement by which tlu-'y are united equally fo, 

 it is plain that the whole concretion muft be extremely- 

 firm, fo as to require very great force to difunite any par- 

 ticle of it from the whole mafs. But if, inftead of employ- 

 ing fand, the only folid body that is entangled among the 

 cementing matter fliould be chalk, (as in all cafes where 

 the mortar confills of pure lime alone,) or any other 

 nightly cohering fubflance, let the cementing particles of 

 that compofition be ever fo perfeft, it is impoflible that the 

 whole can ever attain a great degree of firmnefs, as thefe 

 chalky matters will be eafily broken afunder. 



It is remarked, in addition, that a variety of conjeftures 

 have been made about the nature of the hme cement em- 

 ployed by the ancients. It has been thought that they 

 poffeffed an art of making mortar, which has been long- 

 fince entirely loft ; as the cement in the walls which have 

 been built by them, appears to be, in many cafes, much 

 firmer than that which had been made in modern times. 

 Yet, when the mortar of thefe old buildings is analyfed, it 

 is found to confift of the fame materials, and nearly in the 

 fame proportions, in which they are now made ufe of. 



And 



