28 
M O R 
thing of that opaque calx-like appearance, but aflume 
other colours, and appear more firm, uniform, and com* 
paft ; the fand and other matters that may be enveloped 
in them, being entirely furrounded with a pure cryltalline 
matter. 
To obtain the mod perfect kind of mortar, it is not, 
however, enough that a large proportion of fand fliould 
be employed, and that the fand fhould be intimately 
mixed with the lime; it is all'o of the utmoft importance 
that a large proportion of water be added; for without 
this it is impoffible that a large proportion of the lime can 
be cryftallized ; and the mortar, in that cafe, would conlift 
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 land by itfelf, and iefs 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 im¬ 
portance that the water be retained as long in the mortar 
aspoffible; for if its be fuddenly evaporated, it will not 
only be prevented from afting a fecond time upon the 
lime, after apart of what was firft difi'olved has been cryf- 
tallized, but even the few cryftals that would be formed 
when the water was fuddenly evaporating, would be of 
themfelves much more imperfedt than they othefwife moil 
certainly would have been. In proof of which, inltances 
of the cryftallization of common fait, lump-fugar, and l'u- 
gar-candy, may be adduced ; after which, every one knows 
what a difference there is between the firmnels of the dif¬ 
ferent fubftances ; and that as great muft be the difference 
between the firmnefs of that cement which has been (lowly 
dried, and that which has been haftily hardened by the 
powerful adtion 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 much firmer and more coherent than the mortar that 
was taken from the fame tub and ufed in any work of rna- 
fonry, although in this cafe the materials W'ere exactly the 
fame. From the fame caufe,any 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 may be 
compared to a rnafs of matter confifting of a congeries of 
ftones clofely compared together, and united by a ftrong 
cementing matter that had, while in a fluid ftate, pervaded 
all the interftices between the ftones, and afterwards be¬ 
come a folid indiffoluble fubftance. 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 fiffures, 
that can hardly be broken to pieces by the power of man. 
But, although the cement fhould be equally firm, if the 
Itone, of which it conlifts, be of a foft and friable 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 fo- 
li-d matter cemented by it would give way, and the whole 
would he 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 dif- 
folved, and now cryftallized, which becomes an exceed¬ 
ingly folid and indiffoluble concretion. And as the par¬ 
ticles of fand are of themfelves exceedingly hard, and the 
cement by which they 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 particle of it 
from the whole mafs. But if, inftead of employing land, 
the only folid body that is entangled among the .cement¬ 
ing matter fhould be chalk, (-as in all cafes where the mor¬ 
tar confifts of pure lime alone,) or any other flightly-co- 
Irering fubftance, let the cementing particles of that com- 
jjofitipn be ever fo perfect, it is impoffible that the whole 
TAR, 
can ever attain a great degree of firmnefs, as thefe chalky 
matters will be eafily broken afunder. 
It has already been noticed, that a variety of conjec¬ 
tures have been made about the nature of the lime-cement 
employed by the ancients. It has been thought that they 
pofiefled 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 bad been made in modern times. 
Yet, when the mortar of thefe old buildings is analyfed, 
it is found to conflft of the fame materials, and nearly in 
the fame proportions, in which they are now made ufe of: 
and it is thought probable, that their only fecret confifted 
in mixing the materials more perfectly than the rapidity 
or avarice of modern builders will permit; in employing 
their mortar in a much more fluid ftate than is done now ; 
and in allowing it to dry more flowly, which the immode¬ 
rate thicknefs of many of their walls would naturally pro¬ 
duce, without any preconcerted defign on their part. 
Tradition has even handed down to the prefent times the 
memory of the moft effential of thefe particulars; as the 
lower clafs of people, in every part of the nation, at this 
moment invariably fuppofe and believe that thefe old walls 
were compofed of a mortar fo very thin, as to admit of its 
being poured, like a fluid, between the ftones, 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 ftones in the outer part of the wall, it is 
thought, were probably bedded in mortar nearly as is 
pradtifed at prefent; and the heart, after being packed 
well with irregular ftones, might have the interftices be¬ 
tween them entirely filled up with fluid mortar; which 
would infinuate itfelf into every cranny, and in time ad¬ 
here as firmly as the ftones themfelves, or even more fo, if 
the ftones were of a fandy friable nature. And that, as 
thefe walls were ufually of very great thicknefs, it might 
often happen, that the water in this mortar, by ailing 
fucceflively upon different particles of cauftic lime, would 
at length be entirely abforbed by fucceflive cryftalliza- 
tions, fo as to become perfectly dry, without any evapo¬ 
ration at all; in which cafe, a very large proportion of the 
original lime muft have been regularly cryftallized in a 
flow and tolerably-perfeil manner, fo as to attain a firm¬ 
nefs little inferior to lime-ftone or marble itfelf. 
It is fuppofed that upon thefe principles it is eafy to 
account for the fuperior hardnefs of fome old cements, 
when compared with that of modern times, in which a 
pradtice very different is ufually followed, without hav¬ 
ing recourfe to any wonderful arcana whatever. There 
are unqueltionably, however, many doubtful and myfteri- 
ous circumftances connedted with this matter, which re¬ 
quire the aid of further trials and experience for their full 
explanation. 
There are moreover a few other circumftances that 
may influence the quality of common lime-mortar. If 
lime-ftone be fufficiently calcined, it is deprived of all its 
moifture, and of all its carbonic acid gas, or fixed air. 
But experience (hows, that lime-ftone will fall to powder 
on the effufion of water upon it, when it is much lefs 
perfedtly calcined, and while it ftill retains almoft the 
whole of its fixed air. And, as mafons have hardly any 
other rule forjudging whether lime-ftone be fufficiently 
calcined, except this Angle circumftance of its falling to 
a powder when water is poured upon it, it may thus ea¬ 
fily be perceived, that the fame lime may be more or lefs 
fitted for making good mortar, according to a circunt- 
Itance 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 juft 
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 fel- 
dom happen ; but, as there are a great many intermediate 
degrees between that ftate and perfect calcination, it muft 
often 
