M O R 
©ften happen that the ftone will approach nearer to one of 
thefe extremes at one time than at another , io that the 
mortar may be much more perfect at one time than at 
another, owing to a variation in this particular. 
All tliofe who have written on the fubjeCt of lime as a 
cement, have endeavoured to alcertain what is the due 
proportion of land for making the molt perfeCt cement. 
But a little attention to the matter will Ihoyv, that all rules, 
which could be pre.cribed as to this particular, muft be 
fo vague and uncertain, as to be of little utility to the 
practical mafon ; as, belides the variation which may arife 
from a more or lefs perfeCt degree of calcination as above, 
it is a certain fafr, that fome kinds of lime-ltones are much 
more pure, and contain a much fmaller proportion of 
fand, than others do ; fome being found almoft perfedtly 
pure, while others contain eleven-twelfths of land, and 
all the intermediate proportions of it. Therefore it would 
be abfurd to fay that pure lime would require as fmall a 
proportion of fand to make it into mortar, as that which 
originally contained in itfelf a much larger proportion of 
fand than any writer has ever ventured to propofe for 
being put into mortar. Belides, there are differences 
cauled by the different nature of the calcination in the 
different forts of lime-ffone; from which it may, upon 
-the whole, be concluded, that about one-tenth of pure 
lime-ftone is not enough calcined to admit of being made 
into mortar; and that, of the molt impure forts of lime- 
llone, not above one-fourth part of the lime contained 
in it is lo much calcined as to be in a caultic ftate. The 
variation that is produced by thefe means in regard to the 
proportion of fand that will be required to the lime in 
the one or the other cafe, is found to be fo extremely 
great as hardly to be conceived. It is, how’ever, ftated, 
that the bell: mortar that has been feen made, w'as formed 
of lime which had been found to contain eleven parts of 
find 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 leaft three times its quan¬ 
tity by weight. Therefore, fuppofing that every particle 
of that lime had been fo perfedtly calcined as to be in a 
cauftic ftate, there could not be lefs than forty-leven 
parts of fand to one of lime. As much may, however, 
be allowed for the uncauftic part of the lime as is pleafed, 
and the calculation made accordingly. But it is hardly 
poftible to fuppofe that above one-hundredth part of this 
mafs, independent of the water, coniilted of pure cauftic 
calcareous earth. 
On thefe conftderations, it is conceived that it is impof- 
fible to prefcribe any determinate proportion of fand to 
lime, as that muft vary according to the nature of the 
lime and other incidental circumftances, which would 
form an infinity of exceptions to any general rule. But 
it w'ould 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 fand, when naturally in the lime-ftone, 
is more intimately blended with the lime than can poffi- 
bly be ever effected by any mechanical operation ; fo that 
it would be in vain to hope to make good mortar artifi¬ 
cially from pure lime, with fuch a fmall proportion of 
cauftic calcareous matter as may fometimes be effected 
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 expeditioufiy worked 
than is common, the mortar would be much more per- 
feft than is ufual in modern times, as has been proved 
by aCtual trials. 
It is ftated by fir Humphry Davy, in his work on 
“ Agricultural Chemiftry,” that there are two modes in 
which lime a&s as a cement; in its combination with 
water, and in its combination with carbonic acid. When 
quicklime is rapidly made into a palte with water, it 
foon lofes its foftnefs, and the water and the lime form 
together a folid coherent mafs, which confifts of *7 parts 
VOL, XVI. No.ro 9 o, 
TAR. 29 
of water to 55 parts oflime, When this hydrat of lime, 
while it is confolidating, is mixed with red oxyd of iron, 
alumina, or filica, the mixture becomes harder and more 
coherent than when lime alone is ufed; and it appears 
that this is owing to a certain degree of chemical attrac¬ 
tion between hydrat of lime and thefe bodies; and they 
render it lefs liable to decompofe by the action of the 
carbonic acid in the air, and lefs foluble in water. The 
hardnefs of the mortar in very oid buildings is alfo 
thought to depend upon the perfect converfion of all its 
parts into carbonat of lime. The pureft lime-ltones are 
the belt adapted, it is faid, for making this kind of mor¬ 
tar. The magnefian lime-ftones make excellent water- 
cements, but aft with too little energy upon carbonic 
acid gas to make good common mortar. The Romans, 
on Pliny’s authority, made their belt mortar a year before 
it was ufed, fo that it is fuppofed it was partially com¬ 
bined with carbonic acid gas before it was employed. N 
Mr. Doflie, in the fecond volume of the Memoirs of 
Agriculture, gives the following method of making mor¬ 
tar impenetrable to moifture, acquiring great hardnefs, 
and exceedingly durable, limilar to that ufed by the an¬ 
cients, which was difeovered by a gentleman of Neuf- 
chatel: Take of unllaked lime and of fine fand, in the 
proportion of one part of the lime to three parts of the 
fand, as much as a labourer can well manage at once; 
and then, adding water gradually, mix the whole well to¬ 
gether with a trowel, till it be reduced to the confidence 
of mortar. Apply it immediately, while it is hot, to the 
purpofe, either of mortar, as a cement to brick or ftone, 
or of plafter to the furface of any building. It will then 
ferment for fome days in dry places, and afterwards gra¬ 
dually concrete, or let, and become hard: but in a moiff: 
place it will continue foft for three weeks or more ; though 
it will, at length, attain a firm confidence, even if water 
have fuch accefs to it as to keep the furface wet the 
whole time. After this, it will acquire a ftone-like hard¬ 
nefs, and refill all moifture. The perfection of this mor¬ 
tar depends on the ingredients being thoroughly blended 
together; and the mixture being applied immediately af¬ 
ter to the place where it is wanted. The lime for this 
mortar muft be made of lime-ftone, Ihelis, or marl; and 
the ftronger it is, the better the mortar will be; belides, 
the lime lhould be carefully kept from the accefs of air, 
or wet; otherwile, by attracting moifture, it will lofe pro- 
portionably that power of aCtmg on the fand, by which 
the incorporation.is produced. It is proper alfo to ex¬ 
clude the fun and wind from the mortar for fome days 
after it is applied; that the drying too fall may not pre¬ 
vent the due continuance of the fermentation, w'hich is 
neceflary for the aCtion of the lime on the fand. When 
very great hardnefs and firmnefs are required, the ufing 
of lkimmed milk inftead of water, either wholly or in 
part, will produce the deli red effeCt, and render the mor¬ 
tar extremely tenacious and durable. 
M. Loriot’s mortar, the method of making which was 
announced by order of his majefty at Paris in 1774., is 
made in the following manner: Take one part of brick- 
duft finely fifted, two parts of fine river-fand fkreened, 
and as much old ilaked lime as may be fufficient to form 
mortar with water, in the ufual method, but fo wet as 
to ferve for the flaking of as much powdered quicklime 
as amounts to one-fourth of the whole quantity of brick- 
duft and land. When the materials are well mixed, em¬ 
ploy the compofition quickly, as the leaft delay may ren¬ 
der the application of it imperfeCt or impoffible. Another 
method of making this compofition is to form a mixture 
of the dry materials, i. e. of the fand, brickduft, and pow¬ 
dered quicklime, in the preferibed proportion ; which 
mixture may be put in facks, each containing a quantity 
fufficient for one or two troughs of mortar. The above- 
mentioned old flaked lime and water being prepared apart, 
the mixture is to be made in the manner of plafter, at 
the inftant when it is wanted, and is to be well chafed 
with the trowel. With refpeCt to this method, Dr, ,H\g- 
3 gins 
