QUI

355

QUI

i firm, and durable.

u e j e ? 8 ’ however, been discovered, that the purest lime may

Hi

j *to^ 3 ° 0n cretes into a coherent mass, which fixes to^ in an< ^ ot her rough bodies in a very firm manner,fttiy l his way becomes a proper cement for buildingpHc e ^ 1 °f walls. And that, after this pasty material hasittCatj ff onae firmly dry, it is quite indissoluble in water, and4tng le of ever being softened again by the moisture of theoth er " * ere or other similar causes. Hence it excels many\Vl, 80rts °f cements.

>s Usu Cotn posed for the purpose of building walls, &c., itClt io n - ^^oominated mortar ; bnt when formed as an appli-face *he way of a smooth coating upon any plain sur-ktw.'^out intermixture with stony matters, it is commonlyty-j Plaster.

>8 fi) 611 rna< ’ e from the lime of the purer sort of lime-stone,^g r(!e Un fi to be more soft and crumbly, and to acquire a less'ban ,,,|°^ hardness, and to be broken with much less force,lere the lime-stone, from which it is made, contains aJ lr °P°rtion of sand ; in which case it becomes much

lu ard ''

- .

^ati i er °fi a firm cement by adding a proper proportion of)%| j- arc * sand to it ; hence the practice of blending sandM)i a e > when intended for mortar, has become so universal,^d^t jj v shown to have been very early the case, by theIt j. rQe ~built walls which are now to be met with.

eVe rtheless still remains a desideratum to ascertain theheal j. P° rt 'on of sand necessary, as both writers and prac-Mas aS ° ns ? reatl y disagree in opinion on this matter, ast| al S) la their directions about the mode of mixing the mate-Vi,,, a Pplying the cement; some of the more modern,!Vg (; ‘ y< ascribing extraordinary effects to a small variation ina , tlcu lars, while others deny that these circumstances! sens ifile effect on the durability and firmness of the

It is

°Pini otls COn ceived that these different and contradictory&11Se * rom imperfect knowledge of the nature ofVa Piati 0 ^ e ’ and ti le variations it may admit of; for thesea 8ot(j 3 at 'e so very great, as to render it impossible toan y general rules that can possibly apply in allj i‘?>Poa s p therefore, no doubt, behoves those who are0ri ° acquiring any consistent and satisfactory know-^ this head, to endeavour to ascertain, in the firstC can ? lrcumstan ces which render calcareous substances^'-fal' | )e °f becoming a cement, and then to trace theNi S . langes that may be produced upon it by extraneous

8r%ciic=’ explained the circumstances which cause thejt . e nt n*'' n . ^ mes * one ’ and pointed out the different con-j is krio lltlC 'Pi es °f it> as well as various other peculiarities;: j ’I'lant'it 1 '’ t ' lat i* me which has in any way absorbed its«hog e ti! ^ 0b> a * r f Iom the atmosphere, and become mild,

««„,! ’he i

nnfit for becoming a cement, and that, of course,

i^.havini lai ?p e may be produced upon the quality of any lime,J 1 ' v oi'k ( a J OWed i ess or more of it to be in this state before

Chtity of - _ . „

' V 'tli ^ ! Vater he put to fresh-slaked quick-lime, and beat»• ii port' lnt ° a thin sort of paste, the water dissolves a'°n of the lime, which, as it gradually absorbs its

"P into mortar. And farther, that if a large

into crystals; between the particles of which

Ma 0 tl'6r * at h art °f fhe lime which was not dissolved, andV ‘h ar e eXtraneous matters which may have been mixedPia ^ole entan gied, so as to form a firm coherent mass ofa- "Per, And that the pasty substance formed in thisthe well-known article mortar; and this hetero-

Coq c P er fcctly semi-crystallized mass, constitutes the' 0 q 8i T) e "t employed in building ordinary walls, or othertese circumstances, therefore, being known, it is

thought that it will not be difficult to comprehend what arethe particulars necessary to form the most perfect cement ofthis nature. That since lime becomes a cement only in con-sequence of a certain degree of crystallization taking placein the whole mass, it is sufficiently obvious that the firmnessand perfection of that cement must depend upon the perfec-tion of the crystals; and the hardness of the matters thatare entangled among them; for if the crystals are ever soperfect and hard of themselves, if they be separated fromeach other by any brittle incoherent medium, it is evidentthat the whole mass must remain in some degree brittle andincoherent. That as water can only dissolve a very smallproportion of lime, even when in its most perfect saline orcaustic state, or while it remains deprived of its carbonic acidgas, and, as happens in other similar cases, no more of thelime can be reduced to a crystalline mass than has beenactually dissolved in the water; it follows, of course, that ifmortar be made of pure lime and water alone, a very smallproportion only can be dissolved by that small quantity ofwater that is added to it: and as this small proportion alonecan afterwards be crystallized, all the remaining undissolvedparticles of the lime will be entangled among the few crys- :tals that are formed. And as the undissolved lime in this :mass will in time absorb its air, and be converted into mildcalcareous earth, without having had a sufficiency of water !to allow it to crystallize, it must concrete into a friable mass, ;exactly resembling chalk; this kind of mortar, therefore, :when as dry as it can be made, and in its highest degree of |perfection, will always be soft, and easily crumbled into powder.

But if, instead of forming the mortar of pure lime alone,a large proportion of sand be added to it, the water will, inthis case, dissolve as much of the lime as in the former; andthe particles of hard sand, like sticks or threads, when ma-king sugar-candy or other crystals, while surrounded by thewatery solution, will help to forward the crystallization, andrender it more perfect than it otherwise would have been, soas firmly to cement the particles of sand to each other. Andas the granules of sand are perfectly hard of themselves, so asnot to admit of being broken down like the particles of chalk,it necessarily follows, that the cement made of these mate-rials must be much more perfect, in every respect, than theformer.

After considering a variety of circumstances in regard tothe solubility of lime in water, and its crystallization, it isremarked, that when a large quantity of sand is mixed in themortar, that sand will of course bear a great proportion tothe whole mass; so that the water that may be mixed withthe mortar will be much greater in proportion to the quan-tity of lime contained in this mortar, than if the whole hadconsisted of pure calcareous matter. And that, as the sandabsorbs none of that water, the water, now pure, is at libertyto act once more upon those few particles of caustic lime thatmay still remain in the mortar, which will be dissolved andconverted into crystals in their turn. In this way, it mayhappen, in some circumstances, that a very large proportionof the lime may become crystallized; so that the mortar willconsist almost entirely of sand enveloped in crystalline matter,and become in due time as hard as stone itself; whereasmortar, consisting of pure lime, without sand, can hardlyever be much harder than chalk. It is not, however, to besupposed, that in any case this dried mortar will assume thattransparent crystalline form, or the compact firmness of somesorts of calcareous matters, such as marble and limestone.In mortar, in spite of the utmost care that can ever be taken,a very considerable quantity of the lime must remain undis-solved; which undissolved lime, although it may be so muchseparated by the sand and crystalline limestone as not much