M O R 
impenetrable to water, as to the early defcendants of 
Noah was well known, for both the outfide and the infide 
of the ark was incrufted with it. (Gen. vi. 14.) It may 
be proper to add here, that the bitumen, to deprive it of 
its brittlenefs and render it capable of being applied to 
the brick, muft be boiled with a certain proportion of oil, 
and that it retains its tenacity longeft in a humid litua- 
tion. Mr. Rich informs us, that it is “ at prefent prin¬ 
cipally ufed for caulking boats, coating citterns, baths, 
and other places that ufually come in contact with water. 
The fragments of it fcattered over the ruins of Babylon 
are black, fhining, and brittle, fomewhat refembling pit- 
coal in fubftance and appearancep. 64. 
Mr. Worledge obferves, that fine fand makes weak 
mortar, and that the larger the fand the ftronger the 
mortar. He therefore advifes, that the fand be walked 
before it is mixed ; and adds, that dirty water weakens the 
mortar confiderably. Vitruvius tells us, that foflile fands 
dry fooner than thofe taken out of rivers. Whence he 
adds, the latter is fitted for the infides, the former for 
the outiides, of a building. He fubjoins, that fofille fand, 
lying long in the air, becomes earthy. Palladio takes no¬ 
tice, that of all fands white ones are the worlt; and the 
reafon is owing to their want of afperity. 
The proportion of lime and land in our common mor¬ 
tar is extremely variable : Vitruvius prefcribes three parts 
of pit-fand, and two of river-fand, to one of lime 5 but the 
quantity of fand here feems to be too great. The pro¬ 
portion moll commonly ufed in the mixing of lime and 
fand is, to a bulhel of lime, a buihel and a half of fand ; 
i. e. two parts of lime and three of land ; though the com¬ 
mon mortar, in and about London, has more fand in it 
than according to this proportion. But it ftili remains a 
defideratum to afcertain the due proportion of fand which 
is neceflary, as both writers and practical mafons difagree 
in opinion on this matter, as well in their directions about 
the mode of mixing the materials, as of applying the mor¬ 
tar ; fome of the more modern, efpecially, afcribing ex¬ 
traordinary effects to a fmall variation in thefe particulars, 
while others deny that thefe circumftances have any fen- 
fible effett on the durability and firmnefs of the mortar. 
It is conceived that thefe different and contradictory 
opinions arife from an imperfect knowledge of the nature 
of quick-lime, and the variations it may admit of 5 for 
thefe variations are fo very great, as to render it impoffi- 
ble to afford any general rules that can poffibly apply in 
all cafes. It is therefore conceived to behove thofe who 
are defirous of acquiring any confiftent and fatisfadfory 
knowledge on this head, to endeavour to afcertain, in the 
firft place, the circumftances which render calcareous fub- 
ftances at all capable of becoming a cement, and then to 
trace the feveral changes that may be produced upon it by 
other extraneous caufes. 
Lime, which has in any way abforbed its full quantity 
of air from the atmofphere and become mild, is altoge¬ 
ther unfit for becoming a cement; and of courfe it is evi¬ 
dent, that a great change may be produced upon the qua¬ 
lity of any lime, by having allowed lefs or more of it to 
be in this ftate before it is worked up into mortar. And 
further, if a large quantity of water be put to frefh flaked 
quick-lime, and beat up with it into a thin fort of pafte, 
the water diffolves a fmalfportion of the lime, which, as it 
gradually abforbs its air, is converted into cryftals ; be¬ 
tween the particles of which cryftals, that part of the lime 
which was not diffolved, and the other extraneous matters 
which may have been mixed with it, are entangled, fo as 
to form a firm coherent mafs of the whole. The pafty 
fubftance formed in this manner, is the well-known ar¬ 
ticle mortar; and this heterogeneous, imperfedily femi- 
cryftallized, mafs, conftitutes the common cement em¬ 
ployed in building ordinary walls or other eredtions. 
Thefe circumftances, therefore, being known, it is thought 
that, it will not be difficult to comprehend what are the 
particulars that are neceflary to form the moft perfedl 
T A R. 27 
cement of this nature. Since lime becomes a cement 
only in confequence of a certain degree of cryftallization 
taking place in the whole mafs, it is fufficiently obvious 
that the firmnefs and perfedfion of that cement muft de¬ 
pend upon the perfection of the cryftals, and the hardnefs 
of the matters that are entangled among them ; for, if the 
cryftals are ever fo perfedl and hard of themfelves, if they 
are feparated from one another by any brittle incoherent 
medium, it is evident that the whole mafs muft remain in 
fome degree brittle and incoherent. Now, as water can 
only dilfolve a very fmall proportion of lime, even when 
in its moft perfedl faline or cauftic ftate, or while it re¬ 
mains deprived of its carbonic acid gas, and, as happens 
in other liniilar cafes, no more of the lime can be reduced 
to a cryllalline mafs than has been actually diffolved in the 
water; it happens of courfe, that, if mortar be made of 
pure lime and water alone, a very fmall proportion only 
can be diffolved by that fmall quantity of water that is 
added to it; and, as this fmall proportion alone can after¬ 
wards be cryftallized, all the remaining undilfolved parti¬ 
cles of the lime will be entangled among the few cryftals 
that are formed. And, as the undifl'olved lime in this 
mafs will in time ablbrb its air, and be converted into 
mild calcareous earth without having had a fufficiency of 
water to allow it to crylfallize, it mult concrete into a fri¬ 
able mafs exaftly refembling chalk ; it follows, that this 
kind of mortar, when as dry as it can be made, and in its 
higheft degreeof perfection, will always be foft, andeafily 
crumbled into powder. 
But if, inftead of forming the mortar of pure lime alone, 
a large proportion of fand be added to it, the water will in 
this cafe dilfolve as much of the lime as in the former; 
and the particles of hard fand, like fticks or threads when 
making l'ugar-candy or other cryftals, while furrounded 
by the watery folution, will help to forward the cryftalli¬ 
zation, and render it more perfeCt than it otherwife would 
have been, fo as firmly to cement the particles of fand to 
one another. And, as the granules of fand are perfedliy 
hard of themfelves, fo as not to admit of being broken 
down like the particles of chalk, it necelfarily follows,, 
that the cement made of thefe materials muft be much 
more perfedl in every refpedt than the former. 
After confidering a variety of circumftances in regard 
to the folubility of lime in water, and its cryftallization, 
it is remarked, that, when a large quantity of fand is mixed" 
in the mortar, that fand will ofcourfe bear a great propor¬ 
tion to the whole mafs; fo that the water that may be 
mixed with the mortar will be much greater, in proportion 
to the quantity of lime contained in this mortar, than if the 
whole had coniilled 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 
cauftic lime that may,ftili remain in the mortar, which will 
be diff olved and converted into cryftals in their turn. In 
this way it may happen, in fome circumftances, that a very 
large proportion of the lime may become cryftallized ; fo 
that the mortar will confift almoft entirely of land enve¬ 
loped in cryftalline matter, and become in due time as 
hard as ftone itfelf; whereas mortar, confiding of pure 
lime, without fand, can hardly ever be much harder than 
chalk. It is not, however, to be fuppofed, that in any 
cafe this dried mortar will afl’ume that tranfparent cryftal¬ 
line form, or the compaft firmnefs of fome forts of calcare¬ 
ous matters, fuch a$ marble and lime-ftone. In mortar, 
in fpite of the utmoft care that can ever be taken, a very 
considerable quantity of the lime muft remain undilfolved; 
which undifl'olved lime, although it may be fo much fe¬ 
parated by the fand and cryftalline lime-ltone as not much 
to aft'eft the hardnefs of the mortar, yet it muft ftili retain 
ids white chalk-like appearance. As marble and lime- 
ftone are, however, always formed by thofe particles of 
lime that have been wholly diffolved in water, and from 
which they have been gradually feparated by a more flow 
and more perfeft mode of cryftallization, they have no¬ 
thing 
