MOE
218
MOR
!
l
I
in comparison with ours, might justly be called cement:and that, to our want of knowledge of the materials theyused, is owing the great inferiority of modern buildings intheir durability. But a proper attention to the above parti-culars would soon show, that the durability of the ancientedifices depended on the manner of preparing their mortarmore than on the nature of the materials used. The follow-ing observations will, we think, prove this beyond a possi-bility of doubt.
Lime, which has been slaked and mixed with sand, be-comes hard and consistent when dry, by a process similar tothat which produces natural stalactites in caverns. These arealways formed by water dropping from the roof. But, whenthe small drop of water comes to be exposed to the air, the cal-careous matter contained in it begins to attract carbonic acidfrom the atmosphere. In proportion as it does so, it alsobegins to separate from the water, and to re-assume its nativeform of lime-stone or marble. When the calcareous matteris perfectly crystallized in this manner, it is to all intents andpurposes lime-stone, or marble, of the same consistence asbefore. If lime, in a caustic state, be mixed with water, partof the lime will be dissolved, and will also begin to crystal-lize. The water which parted with the crystallized lime willthen begin to act upon the remainder, which it could not dis-solve before ; and thus the process will continue, either tillthe lime be all reduced to an effete or crystalline state, orsomething hinders the action of the water upon it. It is thiscrystallization which is observed by the workmen when aheapof lime is mixed with water, and left for some time to mace-rate. A hard crust is formed upon the surface, which is igno-rantly called frosting , though it takes place in summer aswell as in winter. If, therefore, the hardness of the lime, orits becoming a cement, depends entirely upon the formationof its crystals, it is evident that the perfection of thecement must depend upon the perfection of the crystals,and the hardness of the matters which are entangled amongthem. *
The additional substances used in the making of mortar, suchas sand, brick-dust, or the like, serve only for a purpose simi-lar to what is answered by sticks put into a vessel full of anysaline solution ; namely, to afford the crystals an opportunityof fastening themselves upon a nucleus. If, therefore, thematter interposed between the crystals of the lime is of afriable, brittle nature, stich as brick-dust or chalk, the mortarwill be of a weak and imperfect kind ; but, when the parti-cles are hard, angular, and very difficult to be broken, such asthose of river or pit sand, the mortar turns out exceedinglygood and strong. That the crystallization may be the moreperfect, a large quantity of water should be used, the ingre-dients be perfectly mixed together, and the drying be as slowas possible. An attention to these particulars, and to thequality of bricks and stones, would make the buildings of themoderns equally durable with those of the ancients. Inthe Roman works, the great thickness of the walls necessarilyrequired a vast length of time to dry. The middle of themwas composed of pebbles thrown in at random, and which evi-dently had thin mortar poured in among them. Thus a greatquantity of the lime would be dissolved, and the crystalliza-tion performed in the most perfect manner. The indefati-gable pains and perseverance for which the Romans were soremarkable in all their undertakings, leave no room to doubtthat they would take care to have the ingredients mixedtogether as well as possible. The consequence of all this is,that the buildings formed in this manner are all as firm as ifcut out of a solid rock ; the mortar being equally hard, if notmore so, than the stones themselves. See Cement, Con-ckete, Grout
Mortar, Hydraulic , sometimes also called Roman cem ^is the composition used in walls under, or exposethe action of water, such as those of harbours, dock 3 ) ^The material best adapted to the manufacture ofmortar is the poorer sorts of limestone, such as contain8 to 25 percent.of foreign matter, in silica,magnesia,
&c. These, when pulverized, absorb water without surelyup, or heating, as a richer lime does, and though calcine tnot slake when moistened, but makes a paste which barin a few days under water, though in the air it never acq 1much solidity. These facts were discovered by Smeat 00 ’^The following analyses of different hydraulic limes jby Berthier, is given by Dr. Ure in his Diet , of A 1 ' 43Manufactures.
A. Analyses of limestones .
Carbonate of lime .
Carbonate of magnesia.
Carbonate of protoxide of iron
Carbonate of manganese .
Silica and alumina .
Oxide of iron.
No. 1.
No. 2.
97 0
2 0
1-0
98-5
1-5
100-0
1000
b. Analyses of the burnt lime .
Lime .
90-4
97-2
Magnesia .
1.8
—
Alumina.
1-8
28
Oxide of iron.
—
—
100 0
100-0
No.
1000
100 0 I
“No. 1, is from the fresh-water lime formationLandon, near Nemours ; No. 2, the large-grained “of Paris ; both of these afford a fat lime when ^ piDelormite affords a pretty fat lime, though it contains ^cent, of carbonate of magnesia; No. 3, is a limes^ p c"the neighbourhood of Paris , which yields a poorsessing no hydraulic property ; No. 4, is the seconstone of Metz; No. 5, is the lime marl of Senonc* ^Dreux ; both the latter have the property of hardenu^.jjwater, particularly the last, which is much used atthis account.”
All good hydraulic mortars must contain a4un ! |I1( , c°''silica ; the oxides of iron and manganese, at one pisidered essential, are rather prejudicial in S redl 1nadding silica and alumina, or merely the former, -gci 11 .circumstances, to fat lime, a water-cement may be ® I)S itnformed ; as also adding to lime any of the folio"' 1
,ef
c,, >%
productions, which contain silicates ; puzzolana, trass v olc <ll l\pumice-stone, basalt-tuff, slate-clay. Puzzolana is ® ^ g0 uJ" eproduct, which forms hills of considerable extent towest of the Appenines, in the district of Rome ,marshes, Viterbo, Bolsena , and in the NeapolitanPuzzuola, whence the name. A similar volcanic tu p er tl> ,e ■in many other parts of the world. Accordingthe Italian puzzolana consists of 44-5 silica ; 1® _
8 - 8 lime; 4-7 magnesia ; 14 potash ; 4T soda :iron and titanium ; 9-2 water ; in 100 parts
The tufa stone, which when ground forms
tra99,
lUitl OIUIIC, WAilV/lA II nvtl -- _. r/M
posed of 57'0 silica, 16-0 clay, 2-6 lime, l'0m a r ^ vv® jppotash, 1 -0 soda, 5 oxides of iron and titanium, , g of 1This tuff is found abundantly filling up valleys m gC j,ist , (Jor 20 feet deep, in the north of Ireland , among V^nhe’ 111formations upon the banks of the Rhine , and at ^
The fatter the lime, the less of it must be a