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Paste es .* one ' ^ tills powder be rapidly formed into a stiffUltim water > it sets or solidifies as a hydrate of lime, andthe a *. e x hardens by the absorption of carbonic acid fromof ]; *' li 1 * 8 constitutes common building-mortar. Hydrate

Cotjjj^ 6 co psists of 100 parts of lime, and 31 parts of water.litt] e pc' limestone consists of carbonate of lime, with very' v hich l otber substance ; it produces a white lime,niuri at - . s fVee, y when well burnt ; it dissolves in dilutedCont a ; IC ac ‘ d ’ w ith only a small portion of residue, and neverext ern ^ lnore than a trace of iron. It differs much instone cba racters, as chalk, marble, common compact lime-

v,,„ lle ^ limestones do not form cements to set in water,hen,, 011 *, 1 ' 16 addition of other kinds of cementing matter ;

Ti, e , J-y are usually employed only for common mortar.litn e , v i' <lest marble and the softest chalk make equally goodPerfe c ,i' e ^ ^urnt 5 hut chalk-lime will slake when notof f lre / mrrnt, an< ] therefore seldom has a sufficient quantitys o r.ir.-’i,' v ^ ereas stone-lime does not re-absorb carbonic acid

_ as chaffi-hme.

'"jury f r Ina ^ e f* oni common limestone, sustains very littleProvij n° IU be! "g l ce P t a i’ ter it has been formed into mortar,?* etl tion ^ a * r be effectua % excluded ; indeed, Alberti

ditch

an

instance of some which had been covered up

cxr.,.11 ^ or a very long time, and yet was found to be ofTo q , Ualit T-r e, Hler it lme alone in the composition of mortar would

I'l. ^ GXrifin c>{ • i _ ?i.. _ . i •» i n • n • i •.

1'lie rrm ex P ens ' ve ; besides, it would be of inferior quality.

'sand e °mm°Tily used to mix with lime is sand, andalso. ti,_ 8 10u ld be of a bard nature, not very fine, but angular;

diis

ft W fi'L 1 " 01 ' 6 ilTe gularPro,

it is in size, the better. It should becored m ' xture °f soft or earthy matter, if it can be

Pos ed '7 without,

sand m a t° ft saruJ

lar d-hn 1 . n ? S ,® 00 d mortar, particularly water-mortar. Very

M es ’ - - -

The reason is obvious; for mortar, com-cannot be harder than that sand. Sea-

a nt brick, or tile, reduced to a coarse powder, alsoParp 0S g s e Xcellent substance to mix with lime, for many?.* ber 'vis' | Ina y he observed, although generally supposed‘me arif j ’ 1 'at there is really no chemical affinity betweenBe t San d,’t is only a mechanical mixture.

"tia itis/Tf observes > that the best mortar is made of puzzo-a,1 <l turjf^, 0 ^ sand > adding, that this penetrates black flints,6a H(l 8 mem white. Mr. Worledge observes, that fine* trotl ger Wea k mortar, and that the larger the sand the, e mortar. He therefore advises, that the sand he)! ea kens ,, e ore it is mixed ; and adds, that dirty waters atl( j ' e mortar considerably. Wolfius recommends thatta fbed . e dr y and sharp, so as to prick the hands when"'ashed ’ I10t so ea i'thy as to foul the water in which it is

ta^ ruv m

for t n he 0a t of

fossif Sides * lbe former for the outsides of a building.- ^all a< j. Sand lying long in the air, becomes earthy.

°!st, fr 01r , ta v i( : s ' n °tice, that of all sands the white are the.The pr 0B ,‘ r "'ant of asperity.

6a e mel y f )0r . t ' on °f lime and sand in our common mortar isanq t anuljle . : Vitruvius prescribes three parts of pit-,?atid her ° r * v er-sand, to one of lime ; but the quantityasp e best ® seems . to be t°° great.

ir Cert ain e ,j P ro portion of sand for common mortar, is easilyp 0i ^ar r ath ^ tr * a ^ ’ enou gl 1 should be added to render thei' 0l> Va r ; er f bort t l* an tough under the trowel. The pro-i a a to j 0 j. e .? mom 4 parts of sand to 1 of lime, or l£ parts ofaifl to Ibe Co 1I ' ae ’ b y measure, the proportion differing accord-Ibe p re arse ness of the sand, the nature of the limestone,cautions used in burning it; all set proportions

a us observes, that fossil sands dry sooner than thosen rivers. "Whence, he adds, the latter is fitted

being universally adhered to only by those who are utterlyignorant of the subject. In many situations, it is impossibleto procure good sand, except at an enormous expense.

Mr. Dossie, in the second volume of the Memoirs of Agriculture, p. 20, &c., gives the following method of makingmortar—impenetrable to moisture, acquiring great hardness,and exceedingly durable—discovered by a gentleman ofNeufcliatel : Take of unslaked lime and of fine sand, in theproportion of one part of the lime to three parts of the sand,as much as a labourer can well manage at once ; and thenadding water gradually, mix the whole well together witha trowel, till it is reduced to the consistence of mortar.Apply it, while hot, to the purpose, either of mortar, as acement to brick or stone, or of plaster to the surface of anybuilding. It will then ferment for some days in dry places,and afterwards gradually concrete or set, and become hard :but in a moist place it will continue soft for three weeks ormore ; though it will, at length, attain a firm consistence,even if water have such access to it as to keep the surfacewet the whole time. The lime for this mortar must be madeof lime-stone, shells, or marl ; and the stronger it is, thebetter the mortar will be. It is proper also to exclude thesun and wind from the mortar, for some days after it isapplied ; that the drying too fast may not prevent the duecontinuance of the fermentation, which is necessary for theaction of the lime on the sand. When a very great hardnessand firmness are required in this mortar, the using of skimmedmilk instead of water, either wholly or in part, will producethe desired effect, and render the mortar extremely tenaciousand durable.

Dr. Higgins, who made a variety of experiments for thepurpose of improving mortar, says, the perfection of lime,prepared for the purpose of making mortar, consists chieflyin its being deprived of its fixed air. On examining severalspecimens of the lime commonly used in building, he foundthat it is seldom or never sufficiently burned ; for they alleffervesced, and yielded more or less fixed air, on the additionof an acid, and slaked slowly, in comparison with well-burnedlime. He also recommends that, as lime owes its excellenceto the expulsion of fixed air from it in the burning, it shouldbe used as soon as possible after it is made, and guarded fromexposure to the air, as much as possible, before it is used.

From other experiments, made with the view of ascertain-ing the best relative proportions of lime, sand, and water, inthe making of mortar, it appeared that those specimens werethe best which contained one part of lime in seven of thesand. Also, that mortar, which is to be used -where it mustdry quickly, ought to be made as stiff as the purpose willadmit, or, with the smallest practicable quantity of water ;and that mortar will not crack, although the lime be used inexcessive quantity, provided it be made stiffer, or to a thickerconsistence, than mortar usually is.

In order to the greatest induration of mortar, it must besuffered to dry gently, and set; the exsiccation must be effectedby temperate air, and not accelerated by the heat of the sunor fire ; it must not be wetted soon after it sets ; and after-wards it ought to be protected from wet as much as possible,until it is completely indurated ; the entry of acidulous gasmust be prevented as much as possible, until the mortar isfinally placed and quiescent; and then it must be as freelyexposed to the open air as the work will admit, in order tosupply acidulous gas, and enable it sooner to sustain the trialsto which mortar is exposed in cementitious buildings, andincrustations.

Dr. Higgins also inquired into the nature of the best sandor gravel for mortar, and into the effects produced by bone-ashes, plaster-powder, charcoal, sulphur, &c., and he deduces

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