QUICK. LIME. 



And it is thought probable, that their only fecrct confifti-d 

 in mixing the materials more perfeftly than the rapidity or 

 avarice of modern builders will permit, in employing their 

 mortar in a much more fluid Hate than is done now, and in 

 allowing it to dry more (lowly, which tlie immoderate 

 thickncfs of many of their walls would naturally produce, 

 without any preconcerted defign on their part. Tradition 

 has even handed down to the prefent times the memory of 

 the mod effential of thefe particulars ; as the lower clafs 

 of people, in every part of the nation, at tliis moment inva- 

 riably fujipofe and believe that thefe old walls were com- 

 pofed of a mortar fo very thin, as to admit of its being 

 poured, like a fluid, between the Itones, after they were 

 laid in the wall : and the appearance of thefe old walls, 

 when taken down, feems to favour this popular tradition. 

 Nor is it doubted but that this may have been the cafe. 

 The Rones in the outer part of the wall, it is thought, 

 were probably bedded in mortar nearly as is praftifed at 

 prefent ; and the heart, after being packed well with irre- 

 gular Hones, might have the interftices between them 

 entirely filled up with iluid mortar, which would infinuate 

 itfelf into every cranny, and in time adhere as firmly as the 

 ' ftones themfelves, or even more fo, if the ibones were of 

 a fandy friable nature. And that, as thefe walls were 

 ufually of very great thickncfs, it might often happen, that 

 the water in this mortar, by afting fucceffively upon dif- 

 ferent particles of cauftic lime, would at length be entirely 

 abiorbed by fucceflive cryftallizations, fo as to become 

 perfeftly dry, without any evaporation at all ; in which 

 cafe, a very large proportion of the original lime mull have 

 been regularly cryftallized in a flow and tolerably perfe£l 

 manner, fo as to attain a firmncfs little inferior to lime Itone 

 or marble itfelf. 



It is fuppofed that, upon thefe pnnciples it is eafy to 

 account for the fuperior hardnefs of fome old cements, when 

 compared with that of modern times, in which a praftice 

 very different is ufually followed, without having recourfe 

 to any wonderful arcana whatever. 



Monficur Loriot, a late French writer, imagined that he 

 had made a perfeft difcovery of the way in which the 

 ancients employed their quick-lime, fo as to obtain fucli an 

 extraordinary firm cement ; from which difcovery, he con- 

 ceived, very important benefits might be derived to fociety. 

 According to his opinion, the ancient cement confiited of 

 lime and fand nearly in the fame proportions as are com- 

 monly employed for that purpofe at prefent. But inftead 

 cf making it of flaked lime entirely, as is done now, he con- 

 tends that they employed a certain proportion of their lime 

 unjlaked, which they mixed with their mortar immediately 

 before it was ufed. And it is further noticed, that this 

 newly difcovered cement dries and hardens almoft under the 

 hand of the operator, without cracks or flaws of any fort ; 

 that it neither expands nor contrafts with the air ; — that it 

 is impervious to moifture, and may not only be employed 

 . for making roofs of houfes that are fubjefted to the con- 

 tinual dropping of water, bafons, aquedufts, canals, &c. 

 which will inllantly contain water in any quantities, but 

 even finer works of the pottery kind ; that it perfetlly 

 refills froits, and has a variety of other interefting qualities. 

 The trials of Dr. Anderfon with the fame fort of materials 

 do not, however, confirm the great certainty and utility of 

 this difcovery. " That fuch enefts as the writer defcribes," 

 fays the doftor, " will invaiiably be produced, merely by 

 adding a certain proportion of unflaked lime in powder to 

 mortar, or even by making the mortar entirely with powdered 

 quick-lime, I may without hefitation venture to deny, not 

 only from the reafoning that has been given, but from 

 Vol. XXIX. 



aftual experiment, again and again repeated by myfelfJ 

 and which is likcwife, in fome meafure, corroborated by th^ 

 experience of Mr. Doflie." 



On thefe accounts, it is fuppofed, that if Monfieur Loriot, 

 has really experienced thefe uncommon effefts from the 

 mortar he has tried, it mull have been occafioned by fome 

 other unobfervcd peculiarity, and not merely by the cir- 

 cumllance to which he feems to alcribe it. Poflibly the 

 doftor fuppofes the lime he employed may have been im- 

 pregnated with a gypfum, or the fulphate of lime, as is 

 probable, for many reafons. The cffe6ts and qualities of 

 which, as to becoming a fine powder, and of fuddenly fel- 

 ting, are well known, but it never acquires the flony 

 hardnefs that lime cement is fometimes endowed with, 

 although it takes the fmoothell pohfli of any cement we 

 know : on which account, it has long been employed as a 

 plaifler where fine ornaments are required. 



There are unqucilionably, however, many doubtful and 

 myfterious circumftanccs coni.edled with this matter, which 

 require the aid of further trials and experience in their full 

 explanation. 



There are flill further a few other circumflances that may 

 influence the quality of common lime-mortar. If lime-flonc 

 be fufficiently calcined, it is deprived of all its moifture, 

 and of all its carbonic acid gas, or fixed air. But ex- 

 perience fhews, that lime-ftone will fall to powder on the 

 effufion of water upon it, when it is much lefs perfeftly 

 calcined, and while it Hill retains almofl the whole of its 

 fixed air. And that as mafons have hardly any other rule 

 for judging whether lime-ftone be fufficiently calcined, ex- 

 cept this fingle circumftance of its faUing to a powder 

 when water is poured upon it, it may thus eafily be per- 

 ceived, that the fame lime may be more or lefs fitted for 

 making good mortar, according to a circumilance that, in 

 a great meafure, eludes the obfervation of operative mafons ; 

 for if it fhould happen that all the pieces of lime drawn 

 from a kiln at one time, were jufl fufficiently calcined to 

 make it fall to a powder with water and no more, that 

 powder would be altogether unfit for making mortar of 

 any kind. This is a cafe that can fcldom happen : but as 

 there are a great many intermediate degrees between that 

 ftate and perfeft calcination, it muft often happen that the 

 ftone will approach nearer to one of thefe extremes at one 

 time than at another ; fo that the mortar may be much more 

 perfeft at one time than at another, owing to a variation in 

 this particular. 



All thofe who have written on the fubjeft of lime as 3 

 cement, have endeavoured to afcertain what is the due 

 proportion of fand for making the moft perfeft cement. 

 But a little attention to the matter will fhew, that aU rules, 

 which could be prefcribed as to this particular, muft be 

 fo vague and uncertain, as to be of little utility to the prac- 

 tical mafon ; as, befides the variation which may arife from 

 a more or lefs perfeft degree of calcination as above, it 

 is a certain faft, that fome kinds of lime-ftones are much 

 more pure, and contain a much fmaller proportion of fand 

 than others do ; fome being found almoft perfeftV)' pure, 

 while others contain eleven-twelfths of fand and all the 

 intermediate proportions of it. Therefore it would be ab- 

 furd to fay that pure lime would require as fmall a propor. 

 tion of fand when made into mortar, as that which originally 

 contained in itfelf a much larger proportion of ftind than 

 amy writer has ever ventured to propofe for being put into 

 mortar. 



Befides, there are differences caufed by the different na- 

 ture of the calcination in the different forts of hme-ftone, 

 from wliich it may, upon the whole, be concluded, that 

 N n about 



