JS1 O R 
common error to fuppofe that the fpirit of fal ammoniac, 
which is moft pungent, contains the greateft quantity of 
fait; but this is not the cafe, for the fpirit made with lime 
is much more pungent than that with fait of tartar, 
though the laft is well known to contain a much larger 
portion of faline particles. 
io. If a piece of paper or linen be wetted in this im¬ 
pregnation, and afterwards dried, it takes fire very 
violently, and fparkles with the fame violence as if it 
were impregnated with falt-petre. 
From thefe experiments it is abundantly proved, that 
the impregnation of mortar contains a large quantity of 
a faline and nitrous ammoniac fait; for a difl'olution of 
lal ammoniac and fpirit of nitre, mixed together, are 
found to produce all the changes in the different bodies 
before named, that the impregnation does. On the whole, 
though it has been fuppol'ed by Mr. Tournefort and 
others, that mortar contained falt-petre, fea-falt, and a 
fixed alkali; yet there does not appear any proof of its 
containing any of thefe falts : no fixed alkali can even be 
feparated from the impregnation of it; and, though the 
linen or paper, wetted in the impregnation of it, fparkled 
when on fire, yet it is not nitre, but merely a nitrous 
fal ammoniac, which occafions that phenomenon. The 
fame effect is produced, if the linen or paper be wetted 
with a mixture of fpirit of urine and fpirit of nitre. And 
the feveral experiments before recited prove, that there 
is in mortar a fpirit of nitre and a fpirit of fea-falt, which, 
with the volatile urinous falts, form a nitrous or a faline 
ammoniac. Mem. Acad. Scienc. Par. 1734. 
Befides the common mortar ufed in laying of bricks 
and ftones, there are feveral other kinds. Thus, for 
inftance, the mortar ufed in making water-courfes, citterns, 
&c. is very hard and durable, being made of lime and 
liogs-greafe, fometimes mixed with the juice of figs, and 
fo'metimes with liquid pitch ; and, after application, is 
walhed over with linfeed-oil. For this purpofe, mortar 
made of terras, pozzolana, tile-duft, or cinders, is mixed 
and prepared in the fame manner as common mortar: 
only that thefe ingredients are mixed with lime, inftead 
of fand, in a due proportion, which is about half and 
half. The lime fliould be made of Ikells or marble; and 
in works which are fometimes dry and fometimes wet, 
inftead of terras, which is very dear, tile-duft or cinder- 
duft may be ufed. 
Plaster, otherwife called white mortar, ufed in coat¬ 
ing walls and ceilings. It confifts of ox or cow hair 
mixed with lime and water, without any fand. The 
common method of making this mortar is one bufliel of 
hair to fix bufliels of lime. But, in this cafe, it is of 
„ great importance to have every particle of the lime-ftone 
flaked before it is worked up; for, as fmoothnefs of the 
furface is the moft material point, if any particles of lime 
fliould be beaten up in it, and employed in work before 
fufficiently fallen, the water, ftill continuing to aft on 
them after it was worked up, would infallibly flake fuch 
particles, which, forcibly expanding themfelves, would 
produce thofe excrefcences on the furface of the plafter 
commonly termed blijlers. Confequently, in order to 
obtain a perfeft kind of plafter that will remain fmooth 
on the furface and free of blifters, there is an abfolute 
necefiity to allow the lime to lie for a confiderable time 
macerating or fouring in water, before it is worked up. 
And the fame fort of procefs is neceflary for the lime 
when intended forufe as mortar, though not fo abfolutely. 
Great care is, however, required in the management in 
this refpeft; the principal things being the getting of 
well-burnt lime, and the allowing it to macerate, or four, 
with the water, for only a veryjhort time before it is ufed; 
but that which is the beft burnt will require the macera¬ 
tion of fome days in the water before it is fufficiently 
flaked in the whole mafs for this purpofe. 
It were much to be wifficd that the art of plaftering 
could be again brought to its ancient perfection. In our 
beft buildings the plaftered walls and ceilings crack and 
Vol. XVI. No. 1090. 
TAR. 33 
fly, and in a little time grow' damp, or moulder to decay. 
The Romans had an art of rendering their works of this 
kind much more firm and durable; and there is no reafon 
to defpair of reviving this art by proper trials. The 
ancient plaftering of thefe people, preferved to this time, 
where it has not met with violent blows or injuries from 
accidents, is ftill found as firm and folid, as free from 
cracks or crevices, and as fmooth and poliihed on the fur¬ 
face, as if made of marble. The bottoms and fides of the 
Roman aquedu&s were made of this plaftering, and 
endured many ages without hurt, unlefs by accidents; 
witnefs that whereof fome yards are ftill to be found on 
the top of the Pont de Gard, near Nifmes, for the fupport 
of which that famous bridge was built to carry water to 
the faid town. The roofs of houfes, and the floors of 
rooms, at Venice, are covered with a fort of plafter, made 
of later date, and yet ftrong enough to endure the fun 
and weather for feveral ages, without cracking or fpoiling, 
and without much injury from the people's feet. The 
fecret of preparing this Venetian plafter is not among us ; 
but it would be worth while to try whether fuch a fub- 
ftance might not be made by boiling the powder of 
gypfum dry over the fire, for it will boil in the manner 
of w'ater; and, when this boiling or re-calcining w r as over, 
the mixing with it refm or pitch, or both together, with 
common fulphur, and the powder of fea-fliells. If thefe 
were all mixed together, the water added to it hot, 
and the matter all kept hot upon the fire till the inftant 
of its being ufed, fo that it might be laid on hot, it is 
poffible this fecret might be hit upon. Wax and oil of 
turpentine may be alfo tried as additions; thefe being the 
common ingredients in fuch cements as we have accounts 
of as the firmeft. Strong ale-wort is by fome directed to 
be ufed, inftead of water, to make mortar of limeftone of 
a more than ordinary ftrength. It is poffible, that the 
ufe of this tenacious liquor to the powdered ingredients 
of this propofed plafter, might greatly add to their folidity 
and firmnefs. Phil. Trdnf. No. 93. 
Stucco is a very curious and ornamental kind of 
plafter, which has been in modern times brought to great 
perfe£tion. Generally fpeaking, it is a compofition of 
white marble pulverized, and mixed with plafter or lime j 
the whole fitted and wrought up with water ; to be ufed 
like common plafter. This is what Pliny means by mar- 
moratum opus, and albarium opus. Of this are made ftatues, 
bulls, baflb relievos, and other ornaments of architecture. 
A Itucco for walls, See. may be formed of the grout or 
putty, made of good ftone-lime, or the lime of cockle- 
Ihells, which is better, properly tempered and fufficiently 
beat, mixed with lharp grit-fand, in a proportion which 
depends on the ftrength of the lime: drift-fand is beft: 
for this purpofe, and it will derive advantage from being 
dried on an iron plate or kiln, fo as not to burn; for thus 
the mortar would be difcoloured. When this is properly 
compounded, it Ihould be put upain fmall parcels againil 
walls, or otherwife, to tnellow, as tho workmen term it; 
reduced again to a foft putty, or pafte, and fpread thin on 
the walls without any under-coat, and well trowelled. 
A fucceeding coat fliould be laid on, before the firft is 
quite dry, which will prevent joints of brick-work appear¬ 
ing through it. Much depends upon the workmen 
giving it tufficient labour, and trowelling it down. If 
this ftucco, when dry, is laid over with boiling linfeed- 
oil, it will laft a long time, and not be liable, when once 
hardened, to the accidents to which common ftucco is 
liable. 
Liardet’s, or, as it is commonly called, Adam's-oil, 
cement, or ftucco, is prepared in the following manner: 
For the firft coat, take twenty-one pounds of fine whiting, 
or oyfter-fhells, or any other fea-fliells calcined, or plafter 
of Paris, or any calcareous material calcined and pounded, 
or any abforbent material whatever, proper for the pur¬ 
pofe ; add white or red lead at pleafure, deducting from 
the other abforbent materials in proportion to the white 
or red lead added; to which put four quarts, beer-mea- 
K fure. 
