c c C V c <: ■fa- c c - < c < €: < <: J- < < c V <: c < c < EXPERIMENTS AND O B S E R V A X I O N S MADE With the View of improving the Art oi COMPOSING and applying CALCAREOUS CEMENTS AND Of preparing Quick-lime: THEORY ofthefeARTS; AND Specification of the Author's cheap and durable Cement, for Building, Incruftation or Stuccoing, and artificial Ston6. By BRT. HIGGINS, M. D. LONDON: Printed for T. Cad ell, oppofite Cat heme- Street, in the Strand, M,DCC,LXXX. [ ^ ] C O N T E N T S. SECTION I. Page R IG IN of thefe experimental Enquiries i SECTION II. Experiments and Ohfervations on Eime-Jlone and Limey — — 3 SECTION m. Remarks on the phlogijlicated Air which ap- peared in fome of the foregoing Experi- ments, — — I4. A SECTION c 0 N r E N r s. SECTION IV. Page j^xperiments Jbewmg that Lime is better for Mortar as it retai?is lefs acidulous Gas, and Jhewing fome of the Caufes of the Im- ferfediion of common Mortar, — 17 SECTION V. Experiments ffiewing how quickly hi me im- bibes acidulous Gas, and is injured by Ex- pofure to Air: Practical InduSiions, ^c. 29 SECTION VI. Mxperiments and Obfervations made to deter- mine whether Mortar be the better for be- ing long kept before it is ufed, — • 37 SECTION VIL Of the Depravation of Mortar by the com- ■ mon Method of ufing the Water ; and of the Ufe of Lime Water, — 43 SECTION C O NT E N r S. SECTION vni. Page Bxpermenis made whh a View to approxi- mate the beji Proportions of Lime Sand and Water ^ for Mortar ^ — 4^ S E C T I O N IX. fkeory of the Induration dependent on the Proportions of Lime and Sand in Mortar, and Obfervations on the had EfeUs of the . vulgar Proportions ofthefe^ — 5 SECTION X, JLxperiments on old Cements, author i%ing the Proportion lately recotnmendcdoj Lme and Sandy ^ 6q SECTION XI. JLxperiments and Ohfervations pewing the Agency of acidulous Gas in the Induration of Mortar, and Circumftancds which im- pede or promote it. Pradtical Inferences, -V 6 z A2 SECTION viil CONTENTS, SECTION XII. Experimentsjhew'mg the beft Kinds and Mix- ^^^"^ lures of Sand, and the beft Method of uftng the Lime ?Faier^ in making Mortar, jzS SECTION XIII. Experiments ftjewing the Efedls of fineft Sand and quartofe Powder in Mortar : Obfervations on the fineft calcareous Cs- ments , P radical Precepts, — 112 SECTION XIV. Experiments made on a larger Scale with our beft Mixture of Sands Ume Water and Lime, — SECTION xy. Experiments fhewing the integrant Paris of Gravel, the Choice and Preparation ofit\ and the Effedls of Clay, Fuller's Earth, and Terras, in Mortar, — j j , SECTION c 0 N r E N r s. SECTION XVI. Page Kxperments fiewing the Effedls of Plajfier Powder, Alum^ Vitriolic Acid, of fame metallic and earthy Salts, and of Alkalies, in Mortar, Pradiical Inferences^ j26 SECTION XVIL ^Experiments fhewtng the EffeSis of Jkimmed Milk, Serum of Ox-Blood, Decodfion of Lijttfeed, Mucilage of Lintfeed, Olive Oil, Lintfeed Oil, and Refn, in Mortar ; and the Effedi of fainting calcareous In- criyjlations, — — i^^ S C T I O N XVIII. Experiments fiewing the Ejfedi of Sulphur, introduced by different Methods, in Mortar, 139 SECTION XIX. Experiments JJiewing the Effedls of Crude Antimony, Regulus of Antimony, Lead Matt, Potters Ore, While Lead, Arfe- nic, Orpiment, Martial Pyrites and faked Mundic, in Mortar, — 143 SECTION £ : C O N rENTS. S £ C T I O N XX. Page Experiments Jhewlng the EffeSls of Iron Scales, wajfjed Cokotkar, native Red Ochres, Tellow Ochres, Umber, Powder of coloured Fluor ^ coloured Mica, Smalt, and other coloured Bodies, in Mortar. Advices concerning cqloured Incrujlaiions, Jnfide Stucco, and damp Walls ^ SECTION XXL Experiment sfiewing the EffeSis of common Wood-afhes, calcined or purer Wqod-afhes^ elixatedJ/hes, Charcoal Powder, Sea Coal- apes, and powdered Coak, jn Mortar \ and Obfervations on their integrant Parts, and the Diferences between them and the Powders of other Bodies, - — I 6 q SECTION XXII. Experiments floewing the Effedls of white- and grey Bone-ajhes, and the Powder of charred Bones ; and 'Theory of the- Agency ef thefe in the befi calcareous Cements, ijz SECTION CONTENTS, xi SECTION XXIII. Page T/jj Specification made in Confequence of Let- ters Patent, illujiraied with Notes ^ 184 SECTION XXIV. Experimental Comparifons of Chalk Lime with Stone Lime. Advices to the Mami- fadiurers of Chalk Lime, concerning the Art of rendering it equal, if not fuperior, to Stone Lime, for the Purpofes of Buil- ders So ap-B oilers and Sugar-Bakers, 206 SECTION XXV. Dire^ions to the Hoifcs already fuccoed with the new Cmient. Obfervatio?is on the Obje5lions of certain Artijh ; on the Cemeniitious Works of the Romans ; on the experienced and unequalled Duration^ of fuch Cements on the Cements of Loriot and others ; ajid on certain Ufes of the Author s Cement, ' ■ — 214 SECTION SECTION L AMONGST the inft^iices and experi- ments produced in my public Courfes bfChemiftry in 1774, to illuftrate my no- tions of the polarity of matter, divers mix- tures of lime fand and water, were parti- cularly confidered : and thefe being preferved and methodically arranged, according to the plan of this fchool, foon fuggefted to me an enquiry which I have profecuted with great attention ever fince that time; As the ftrength and duration of our moft tifeful and expenfive buildings depend chiefly on the goodnefs of the cement with which they are conftrudled, I looked to the im- provement of mortar aS a fubje(ft of great importance, in this Country particularly, where the weather is fo*variable and trying, and the mortar commonly ufed is fo bad, B that to til at the timbers of houfes laft longer tliart the walls, unlefs the mouldering cement be frequently replaced by pointing. But feeing that many years are requifite for the greateft degree of induration which Cementitious mixtures like mortar can acquire, or for our aifcovering the imperfedlions of them ; and that the life of man, is too fhort to allow any connderable improvements of them to be derived from fuch. experiments as had, hi- therto been made, 1 refolved in the begin- ning of the year 1775 to invefllgate more clofely than I had hitherto done, the princi- ples on which the induration and ftrength of calcarioUs cements depend ; not doubting that this would lead me by an untried path to recover or to excel the Roman cement, which in aqueduds and the moft expofed Qrudures has withflood every trial of fifteen hundred or two thoufand years. SECTION [ 3 3 SECTION II. 'Experiments and OhferDatwns oh Lime-Jloni md Limei IHad already learned from the fchafte and phllofophic prddu6i:iori3 of Dr. Blacky that calcarious ftones which burii to lime, contain a confiderable quantity of the elaftic fluid called fixable air or aciduloiis gas, which in combination with the earthy mat- ter fdrms a great part of the mafs and weight of thefe flones ; and that the dif- ference between lime-ftone or chalk and lime, eonfifts chiefly in the retention or ex- pulfiori of this matter* Expecting to learn fdmethirig further relative to lime, and particularly, to difcover the caufe of the differences which appear ni cements made with different kinds of lime^ I made the following experiments^ I PROCURED fpecimens of different kinds of hme-flone and chalk, and breaking them B 2 into [ 4 ] into fmall fragments, I burned them in cru- cibles lined with lime to prevent the pieces from touching their crucibles and vitrifynig at thofe furfaces which lay next to them : I like- wife burned the like fpecimens in crucibles perforated to admit a free current of air through them ; and laftly, I expofed three pounds of either fpecimen to a graduated fire in an earthen retort which was barely fuffi- cient to hold this quantity, and whofe neck I lengthened by fitting to it a glafs conical tube luted at the jundure with four parts of lime one of fine fand and as much diffolved glue fuch as the carpenters ufe, as was fufficient to form a pafte ; having found this luting to hold faft and to be impervious to any elaftic fluid or liquor expelled in fuch procefles. 1 immerfed the extremity of the glafs tube in mercury, and inverting a bottle filled with mercury over the extremity of the tube, I received whatever water or elaf- tic fluid was expelled from the calcarious ftones by the fire, and I meafured the quan* tity of thefe by inftantly applying a frefli bottle as foon as the former was filled. When all the water was expelled, or when I knew the quantity of it contained in the lime- [ 5 \ lime-flone or c!talk, I ufed a bafon of water and bottles filled with water, making allow- ance for the matter imbibed by the water. To avoid a tedious detail of particular^ which do not imm.ediately relate to the chief objea of this ellay, 1 flrall only mention lummarily the mod pertinent obfervations which thefe and other experiments afforded ; endeavouring that the terms in which I Ihali deliver'^thefe obfervations ^lall defcribe the experiments fufficiently for thofe who ^ire acc^uainted with modern chemiftry. Observation i. Lime-stone or chalk heated only to red^ nefs, in a covered crucible, or in a perforated crucible through which the air circulates freely, loofes only about one-fourth of it's weight, hov/ever long this heat be continued. The fort of lime fo formed effervefces confi- derably in acids, flakes ilowly and partially to a powder which is not Vv^iite, but is grey or brown, and heats but little in flaking. In defcribing heats I do not^rcgard the heat in- particular parts of the fuel, but B 3 ■ ^-^^7 [ 6 ] only that which the bodies themfelves are made to conceive equally through their whole mafs, whether they be in vefTels which defend them confiderabiy from the adion of the fire, or fully expofed to it by tjieir immediate conta£l with the fuel. Observation. 2. Lime- 5 TONE pr chalk expofed to a Ixeat bare- ly fufficient to' melt copper, whether in a perforated crucible or otherwife, lofes about one third of its weight in twelve hours, and very little more in any longer time. This lime efFervefces but (lightly in acids; it heats; much fooner and more llrongly than the foregoing, when water is fprinkled on it, and it (lakes more equably and to a whiter powder. In a variety of tfials, this lime appeared to be in the farqe (late with the bed: pieces of lime, prepared in the com- mon lime-kilns. For the quantities of aci- dulous gas obtainable froni both by a Wronger heat, or in folutipn, were nearly equal ; they flaked in equal times, with the fame phenomena, and to the fame colour an4 condition of the powder. O B s E R- t 7 ] Observation. 3. The lime burned In perforated crucibleg, or in the naked fire, is whiter than that burned in common crucibles covered, m which cafe the air has not fo free accefs to it ; altho' the lofs of weight be the fame in both ; but this latter kind of lime, in flaking, affords as white a powder as any other which has loft equally of it§ weight. What- ever portion of phlogifton it retains to pro- duce this dulky colour, is either detached in the flaking, or does not fenfibly affed the lime in any ufe, to which I applied it. Observation. 4. When dry chalk or lime-ftone is ufed, in the procefs above defcribed for making lime in clofe veflels, and for examining the matter which is expelled by fire, the quantiry of water obtainable from it by any heat, is fo inconfiderable as to deferve no noti<:e in our menfuration of that matter. Observation. 5. Chalk or lime-ftone heated gradually in thefe clofe veflels, lofes very httle acidulous gas until it begins to redden : after this the B 4 elaftic [ 8 ] elaftic flui-d ifTiies from it the quicker as the heat is made greater, and continues to iflue Wntil the retort glouvs with a vivid white heat fufiicient to melt fteel^ Observation. 6 Forty-eight ounces of ch^^lk yield twen- ty-one ounces of elaftic fluid, the firfl por- tions tif* which are turbid as they iffue, but foon become clear without lofs of bulk, by the condenfation of the watery vapour : the remaining portions ilfue tranfparent and in- vifible. One thirty-fixth of this elaftic flLiid, and fometimes much more of it, is phlogiflig air, the remainder is pure acidulous gas. Observation. 7 ' The refiduary lime of forty-eight ouaces of chalk, urged with fuch heat to the tbt^ expulfion of the elaftic fluids, weighs e>aly twenty-feven ounces, whilfl it is red hot. When it cools it weighs more by reafon of the air which it imbibes as tlie fire efcape^ from iu O B 5 E R- [ ^1 Observation When no more heat is employed than b necefiary for . the expiilfion of thefe elaftic fluids, the refiduary matter is found cou- tra6led fenfibly in volume, and is good lime, tho' not fo white as lime prepared in the ufual way. With water it flakes inftantly, grows hilling hot and perfectly white. The flaked powder is exceedingly fine, except in thofe parts of the lime which lay in conta(3: with the retort, which are always fuperii- pially vitrified, becaufe clay and lime pro- fnote the vitrification of each other, ^ Ob serva tion 9. The lumps of this lime, immerfed in Hine' water, or boiling water, to expel the sir which fuch fpongy bodies imbibe in cooling, diffolve in marine acid without fhewing any fign of effervefcencc. Observation 10. LiME-STONE or chalk gradually heated in a crucible, or on the bed of a reverberatory furnace, or in contaQ: with the fuel in a wind furnace, does not become perfeclly ;jionclFervefcent and fimilarto the lime lafl de- fcribed [ 1° J fcribed, in flaking inftantly, and growing hiffing hot when water is fprinkled on it, ■until it has, after a ftrong red heat of fix of eight hours, fuflained a white heat for an hour or more. I underftand by a white heat, that which is fufficient to melt call: iron compleatly, O B S E RVA T I O N. II. Lime-stones heated fufficiently to reduce them to lime which flakes inftantly with the figns above defcribed, and which is perfedtlj nonefFervefcent, do not in general lofe fo much of their weight as chalk-flione does, under the like treatment. Some lime- ftones lofe little more than a third of their weight. Thofe which lofe the rnoft, flake the quickefl and to the finefl: pow- der ; and thofe which lofe the leaft,, flake the floweft and to a gritty powder com- pofed of true lime and particles chiefly gyp^ feous. Observation, iz. The quantity of gypfum, or of other earthy matter in well burned lime, is difcover^ able by weak marine acid ; for this difTolve? and r " 1 and waflies away the lime, leaving the gyp;- fum to be meafured when dry, the part of the gypfum which diflblyes being too Imall |:o deferve any attention ; and if any other earthy matter or any faline matter exifted in the lime-ftone, it vitrifies with part of the calcarious matter in the heat neceffary for niaking noneffervefcefit lime, and is feparable j3y the means laft mentioned, and even by ^ jfine fieve in mofl: inflances. Observation. 13. When lime-ftone or chalk is fuddenly heated to the higheft degree above defcribed, or a little more, it vitrifies in the parts which touch the fire veflels, or furnace, or fuel, and the whole of it becomes incapable of flaking freely or afting like lime. Lime-ftone is the more apt to vitrify in fuch circum- ilances, as it contains more gypfeous or argilla- ceous particles ; and oyfter-fhells or cockle- fhells vitrify more eafily than lime-fl:one or chalk, when they are fuddenly heated ; which I impute to their faline matter ; for i^hen they are long weathered, they dp not yitrjfy fo eafily. P B S E R- [ i Observation. 14. The agency of air is no further necelTary in the preparation of lime, than as it operates in, the combuftion of the fuel. Observation. ^5. Calcarious flones acquire the properties t)f lime in the moft eminent degree, when they are flowly heated in fmall fragments until they appear to glow with a white heat, when this is continued until they become nonefFervefeent, but is not augmented. The art of preparing good lime conlifts chiefly in thefe particulars. Observation 16, That lime is to be accounted the purefl and fitteft for experiment, whether it be the beft for mortar or not, which flakes the. quickell; and heats the moft in flaking, which is whiteft and finefl: when flaked, which when wetted with lime-water diflbivei; in marine acid or diitiiled vme2:ar w^ithont efFervefeence, and leaves the fmaliefl; quantity of refiduary undiflblved matter. O E S E R- [ »3 3 Observatiok 17. The quick flaking, the colour of the flaked powder, and the former acid, arc the mofl: convenient, and perhaps the beft tefts of the purity of lime. The whitenefs denotes the lime to be free from metallic im* pregnation; the others Ihew any imperfec-* tions in the procefs of burning, and the he- terogeneous matter infeparable from the calcareous earth by burning. SECTION [ H J SECTION IIL Remarks on the Phlogljilcated Air which ap^ peared In fome of the foregoing Experiments, AS phlogiftlcated air had not been no- ticed in any experiment heretofore made on chalk or Hme-ftone, I refolved t6 examine the elaftic fluid detached from them in the ufual method, I extricated feveral gallons 6f elaftic fluid from chalk, during the folution of it in marine acid diluted largely with water ; and after agitating this elaftic fluid with the necef- fary quantity of water^ and fometimes with lime-water, until all the acidulous gas was- imbibed by them, I found a refidue con- fifting of common air, which was about one twenty-eighth of the bulk of the acidulous gas, in fome trials, in others it was much lefs. As I have not had time to examine lime- ftones in the fame manner, or to profecute this [ 15 ] this fubjecl by other experiments, and as it does not appear fufficiently interefting in our prefent enquiry concerning calcareous ce- itients, I muft content myfelf with offering a conje6ture concerning it." The air which is extricated during the {o- lution of chalk, feems to be that which chalk, like other porous bodies, imbibes by capillary attraction ; and it retains its proper character, becaufe all the phlogiftic matter of chalk is held in the folution. It may happen likewife that fome air efcapes from the ^vater whilft it imbibes the acidulous gas, which it attradls more forcibly ; and this air from the water may contribute to the bulk of that which appears in the folution of calcarious bodies. But whilfl: chalk is de- prived of its acidulous gas by the adion of hre, the air which was held in its pores, and which attracts phlogifton, is expelled in combination with phlogifton, and confe- quently in the form of phlogiftic air ; and the air contained in the pores and in the cavity of the retort, contributes to the bulk of the phlogiftic air obtainable in this manner. This t |6 1 This conjefture appears the more probable tvhen we cpnfider, that the (quantity of aif imbibed by porou§ bodies is much greatei" than it appears in any experiraents m^jde with the air pump ; as I Ihewed iia ray public courfe of chemiftry in 1776, by the great Increafe of weight, which red hot charcoal acquired in cooling in veflels into which nothing ponderable but air was admitted.^ The fame attractive powers which draw air into bodies, and condenfe it in them, refill: the expanfion and efcape of it in the void ; ^nd detain, in fuch a fituation of the bodies, that quantity, whofe repulfive powers are counterpoifed by the attradive powers. SECTION 1^1 1 S E C T I O N IV. Experimenh /hewing that Lime is better fof Mortar as it retains iefs acidulous Gas, and Jhewing fome of the Caufes of the Imperfect ioti of common Mortar k ON divers confiderations it appeared td me, that the perfection of lime foi? mortar confifts chiefly in the total expulfion of the acidulous gas ; but to be better fatis- fied of the truth of this opinion, I made fe- veral parcels of mortar, the defcription of which will be abridged by obferving in this place concerning all of them, that the fand employed was coarfe Thames fand, fuch as I ufe in my fand baths ; that the lime was flaked as foon as it cooled after being burned, and with the fmalleft quantity of water ne- ceflary for this purpofe ; that it was fifted through a fine brafs wired fieve as foon as it was fully flaked ; and that each parcel of mortar was beaten and brilkly formed with the quantity of water which was barely fuffi- cient to give it the ufual eonfiflence, which. G quantity I i8 ] ^quantity I fhall exprefs in tlie pharmaceu- tical method by defcribed in obf. i, fe£t. 2, but formed of the beft lime-ftone, * Water, q. f. , C 2 xo. Sand, 10. Sand, — — 5 The foregoing lime, — % Wat€r, q. f, 1 1. Sand, — Imperfea chalk lime defcribed in obf. i, fed. 2, — — Water, q. ^, 12. Sand, — . 6 The laft mentioned lime — | Water, q. f. The lime of the 9, 10, ir, and 12 fpe- cimens was flaked whilft it was hiffing hot, in a covered vefTel ; becaufe it would not •flake fufficiently when it was fuffered to cool before the water was fprinkled on it, or when it's heat was foon diffipated by a free expofure to the air and hafty evaporation of the water : And as this hme required feveral hours to flake, I put it into a bottle as foon as it was cool, and kept it weU flopped for twenty-four hours before I flfted it. At [ ^' 1 At the fame time I made two fpecimens of mortar with common chalk lime and fand in the foregoing manner. Each fpecimen was fpread as foon as it was made, to the thicknefs of half an inch on a plain tile previoufly foaked in water ; the tiles were numbered and kept clofe by each other in an airy part of my elaboratory until the mortar was dry, and then they were equally expofed, ftanding upright, in a place where the air fun and rain had free accefs to them* In the courfe of fourteen or fifteen months thefe fpecimens afforded me a great deal of information, which will be noticed in due time ; even in the firft fix months they ftiewed me clearly that lime is. the better for mortar as it is more perfe(^tly freed from acidulous, gas. For when the eomparifon was made between fpecimens of mortar confining of the fame quantities of Ume and fand, I found that the mortar made with well burned non- effervefcent lime, hardened fooner and to a much greater degree, than mortar made with common lime or my flone or chalk lime C 3 burned [ 22 ] burned in the manner expreffed in the fecond pbfervation of the fecond fedlion : and the fpecimens made with the ftone or chalk lime which was leaft burned, were incomparably ■ivorfe than any of the others ; for they never acquired any confiderable hardnefs, and they mouldered in the winter, the fooner as they contained more of the lime and cracked more in drying. I obferved that the fpecimens w^hich con-; tained the fmaller quantities of well burned lime cracked much lefs than the others, or not at all ; that they adhered to the tiles more firmly, and were lefs injured by freezing ; but as the fpecimens made with an excefs of the beft burned lime were not more cracked than thofe made with equal quantities of the other kinds of lime, and as I could diftinguifh the im- perfe(5tions arifing from theexcefsofUme, from thofe which proceeded from the bad quality of it, I was fatisfied that the lime which is- moft compleatly burned is the beft for mortar. Considering the heat, which I found ne- ceffary to extricate the lafl portions of acidu- Jpus gas from chalk or lime-flone, to be much greater [ 23 ] greater than what is ever excited in makings lime in this country or elfewhere, fo far as I had obferved or could learn from others ; I fufpefted that the lime commonly ufed in building is feldom or never fufficiently burned. On repeated trials of feveral fpecimens of fuch lime, I found this fufpicion to be well founded, for they all efFervefced and yielded acidulous gas, more or lefs, during the folu- tionof them, and flaked llowly in compa- rifon with well burned lime. To render the efFervefcence confpicuous, a ftrong acid ought to be ufed, becaufe the quantity of water in a diluted acid, retains a proportional fhare of the acidulous gas, and a certain quantity will retain the whole of it, and prevent the efFervefcence ; becaufe the ef- fervefcence depends on the efcape of the elaflic fluid out of the folution. This is exemplified in the mixture of diluted vitriolic acid with the diluted folution of fait of tartar, lately re- commended as a medicine by Dr.Hulme : for thefe folutions mix without effervefcence ; although a more concentrated folution of the C4 ^^^^^ t ^4 3 ftlkali mixed with vitriolic acid effervefces violently, By feveral experiments, the relation of which is not neceffary for thofe who are in- ftnifted in chemiftry, and would be uninte- rafting to others, I found that the chalk lime lifed in London, when taken as frefh as it can be had at the lime-wharf near Blackfriars- bridge, confills of pieces which being the beft burned contain, efpecially in their cen- tral parts, about one-twentieth of their weight of acidulous gas ; of others which contain more ; and of others which retain near half their original quantity; that thefe laft are eafily difcoverable by their fpecifie gravity and hardnefs ; and that this is the part of our common lime, which flakes the latefl: and of the dufkiefl: colour, or which never flakes at: all. On a peck of this lime I fprinkled water, endeavouring to flake it equably by throwing the mofl: water on thofe pieces which re- quired it mofl:. After the lime had flood a quarter of an hour, to flake, I fifted it through g fieve whofe apertures were fquares of one ' flxteenth [ ] dxtecnth of an Inch ; and then meafuring the part which could not pafs through the lleve, I found it to be about one fifth part of a peck, I fprinkled boiling water on this coarfe part, and put it in a clofe veflel in a warm place to accelerate the flaking of it. I made a parcel of mortar with one part of the fifted lime and three of fand with a fuffi- cient quantity of water ; and another parcel with one part of the lime fix of fand and the neceflary quantity of water ; and I tried them upon tiles in the manner already related, in the month of April, the weather being The foregoing coarfe portion of the lime, after three hours, was flaked in feveral parts to a greyifh powder, and I could perceive that more of it would flake in a longer time. I anticipated this by reducing the un- flaked part to powder and mixing them toge- ther, With [ 26 ] With this powder and fand and water iii the foregoing proportions I made two fpeci- piens of mortar, and expofed thenqi as I had idone by the former. In a few months it appeared that the fpe^ jcimens laft mentioned fcarcely deferved the name of mortar ; whilft thofe made with the firft flaked part of the hme, were but little inferior to the beft fpecimens made with the •fame proportions gf chalk lime and fand. These experiments confirmed me in the opinion that lime is the better for mortar as it is freer from acidulous gas ; they fhewed one of the caufes of the badnefs of our com- mon mortar ; and how to manage ill-burnt lime, when better cannot be had? The workmen ufually flake the lime mixed with the fand or gravel in great heaps, and do not fkreen it until the moft part is debafed by that which flakes after five or fix hours or more, and which is little bet- ter than fo much powder of chalk. But if thv*y would Ikreen the lime in about half an [ ^7 1 hour after the water is thrown on it, the mortar would be much better, although the quantity of lime in it fhould be much lefs 5 for I obferved in all the foregoing fpecimens, that thofe which contained the fmalleft quantity of lime were the beft ; and this; quantity is rnuch fmaller than is ufually em- ployed in making mortar. These remarks are applicable to mortar piade with ftone-lune ; though the ftone-lime be generally better than the chalk-lime ufed in London, becaufe they are obliged to burn it better, as it will not flake otherwife. In the brief relation of thefe experiments I |iave taken no notice of the flint kernels which frequently occur in chalk-lime, or of the pther fl:oney mafles different from the cal- parious, which are found in lime-flone ; be- paufe I took care that they fliould not lead fne into any errors. When firfl: I noticed the quantity of chalk- Jime which flakes latell: or not at all, I fuf- pe£led that this difference might in fome de- gree be owing to the admixture of argillaceous or [ 28 ] or other matter ; but on trying thefe parts in acids, and after burning feveral fpecimens of them, I was convinced that the only impe- diment to their flacking confifted in their liot being fufficiently burnt in the kihi. SECTION [ 29 3 SECTION V. Experiments Jhewing how qtdckly lime imbibes aci* dulous gas, and is injured by Expofure to Air : Practical Indudtions^ &c» IT was already known that lime expofed to air gradually lofes thofe charaders which chiefly diftinguifh lime from whiting or powder of chalk, and that it refumes the acidulous gas which had been expelled from it in burning. But as I was defirous to know in what meafure or time thefe changes take place, and in what circumftances they are accelerated or retarded, I made the following Experiments. • On the 22d of Augufl 1776 1 expofed two pounds avoirdupoife of well-burned noneffer- vefcent chalk lime, in fragments of the fize of a walnut fpread on a board, in a dry un- frequented room. I expofed the fame quan- tity of this lime, at the fame time and in the fame manner, in a paliage through which there was a conflant current of air ; and I put i 3° i put the fame quantity of this lime, in frag- ments of the fame lize, in a box which might hold as much more of it, and placed the box loofely covered with its lidj clofe by the firft portion of lime; In 24 hours the fuperficial lumps of the lirft parcel cracked in fome parts a little, thofe of the fecond cracked more, thofe of the third were not vifibly altered. In forty-eight hours the firft parcel cracked fo much as to fall into fmaller fragments on being moved, and thefe were reducible to powder by pref- fulg them between the fingers : The fecond parcel underwent the like or rather a greater change, for it was more cracked and friable : 'The third now begun to crack in the fu- perficial parts. ^ On weighing theni, I found that the firft parcel weighed two pounds five ounces, the fecond two pounds fix ounces and one drachm, the third two pounds one ounce ten drachms: I then returned them to their former Na- tions. In [ 3' ] In fix days the firft parcel weighed two pounds ten ounces feven drachms ; the fe- cond two pounds twelve ounces one drachm ; the third two pounds four ounces eight drachms. In twenty-one days the firft parcel weighed three pounds one drachm ; the fecond three pounds two ounces one drachm and a half; the third two pounds fix ounces ejght drachms. During this increafe of weight the frag- ments fplit into fmaller pieces, but did not fall into powder, except in a fmall part of them, or when they were handled. By fimilar experiments made on well burned flone lime I found that this imbibes matter from the air nearly in the fame manner as chalk lime, but rather more flowly ; which I think is owing to its clofer texture. On expofing common chalk or flone lime in the fame way, 1 find that it increafes in weight much lefs and more llowly. t 3^ 1 To difcover the quantity of water which the lime imbibed from the air, and which con^ tributed to this increafe of weight, I put each parcel in a glafs retort ; and adjufting to it my apparatus whereby all that is con- denfible is faved, whilft elaflic fluids are at liberty to efcape, I found that the quantity of water contained in each parcel of lime, was nearly in fome, and in others accu- rately one-twenty-fourth of the gained weight, the remainder of the weight gained was of acidulous gas mixed with a little air, which latter I do not reckon, becaufe it was already weighed in the lime. If a glafs bottle be filled with fragments of well-burned chalk lime, or ftone lime, or (hell lime, and well flopped with a ground glafs ftopple nightly waxed where it fits the neck of the bottle, the lime will remain un- altered in weight, or in any other known particular, for a year or two ; as I have re- peatedly experienced : even the phofphoref- cence of lime is thus preferved in its full luftre, for a year or more. Thus it appeared that well burned lime imbibes [ 33 ] imbibes acidulous gas from the air, the fooner as it is the more fully expofed to it : that lime imbibes this matter from the open air, the more greedily as it is more per^ fe£liy deprived of it previous to the expofure : that lime cannot be long preferved unal- tered in any veffels which are not perfectly air-tight, but may be kept uninjured for any time in air-tight veffels filled with it: that chalk lime, by reafon of its fponginefs, or by fome other condition of it, requires to be kept lefs expofed than ftone lime, and well burnt lime lefs expofed than common lime, to render the depravation of them equal in equal times : that if iicidulous gas imbibed bv lime previous to its being ufed in mortar, be as injurious to the mortar, as the acidulous gas retained in equal quantity by ill-burned Jime is, lime grows the more unfit for mortar every hour that it is kept expofed to air, whether in a heap, or in calks pervious to air. I THINK moreover that thefe experiments fhew that lime undergoes thefe changes by expofure, much quicker than has been fuf- peded ; fince wxU burned chalk lime kept in D ^ [ 3^ ] a dfy room, imbibes near a pound of acidulous gas in three weeks, in the fummer feafon. Not to trufl to theory what I could prove by experiment, I did not reft fatisfied with the obfervations and reafons which mi^ht perfuade one that lime, which has imbibed fome acidulous gas, is as unfit for the ufes now under confideration, as lime which re- tains an equal quantity of the like matter by reafon of the deficiency of heat in burn- ing it. I TRIED parcels of well burned chalk and flone lime, fome of which were ufed frefh, others expofed two days, others fix days, others twenty-one days, in the fame circum- ftances ; by making feveral fpecimens of mortar with them, and expofing the fpeci- mens in the nianner already related : and in a few months I was fatisfied that the fpeci- mens made with frefh lime were the hardefi: and beft, and that the others were worfe as the lime of them had been longer expofed : for thofe made with the lime which had been expofed three weeks and had gained fpur or five ounces to each pound, were fo eafil^ [ 35 J eafily cut or broke, fo much affecled by moifture and drying, and lb liable to break off from the tiles, as to be utterly unfit for the ordinary ufes of mortar. After this there remainedno doubt thatiime grows worfe for mortar every day that it is kept in the ufual manner in heaps or in crazy calks ; that the workmen are miftaken in thinking that it is fufficient to keep it dry ; that lime niny be grea tly debafed without flaking fen- fibly; and that the luperficial parts, of any parcel of lime, which fldl into fmall fragments or powder without being wetted, and merely by expofure to air, are quite unfit for mortar ; fmce this does not happen until they hav^ imbibed a great deal of acidulous ga^. I NOW faw more clearly another caufe of the imperfedlion of our common cements. The lime beino; exnofed a confiderable time before it is made into mortar, and drinking in acidulous gas all the while, the quicker as it is the better burned, is incapable of ading like good lime, when it is made into mortar ; and often approaches to the condition of whiting, which with fand and water makes D 2 a [ S6 ] a friable perlfhable mafs, however carefuliy it be dried. In London particularly they life lime which i.-. burned, at the diftance of ten or twenty miles or more, in Kent and elfe- where, with an inlufficicnt quantity of fuel. This lime remains in the kiln, to which the air has accefs, for many hours after it is burned. It is expofed for fome days in the tranfportation, and on the Hme-wharfs ; and it undergoes further expofure and carriage before the artift flakes it for mortar. It is no wonder that the London mortar is bad, if the imperfection of it depended folely on the badnefs of the lime ; fince the lime employed in it, is not o^ly bad when it comes frefh from the kiln, but becomes worfe before it is ufed, and when flaked is as widely diiierent from good lime, as it is from powdered chalk. SECTION [ 37 3 SECTION VI. ll'xp'erimetiis and OhferDations rnade to determine whether Mortar be the better for being long kept before it is ufed. I AM generally difpofed to think that there is fome good reafon for any prac- tice which is common to all men of the fame trade, although it may not be eafily reconcilable to the notions of others: and feeing that the builders flake a great quan- tity of lime at once, more than they can ufe for fome days, and that all thofe, whom I converfed with, efteemed mortar to be the better for being long made before it is ufed; and that plaifterers particularly follow this opinion in making their finer mortar or ftucco for plaifcering within-doors ; I was defirous to difcover the grounds of thefe meafures fo repugnant to the notions gathered from the foregoing experiments and others. In the month of March 1777 I made about a peck of mortar, with o^ie part of the D 3 freflieft [ 38 1 frefheft and beft chalk lime flaked, fix parts of fand, and water q. f ; for in a great number of experiments, I cbferved that this propor- tion of lime was better than any larger which I had tried, or which the workmen obfervc in making mortar. 1 FORMED the mortar into an hemifphe- rical heap on the paved" floor of a damp cel- lar, where it remained untouched twenty- four days. At the expiration of this time, I found it hardened at the furface ; but moifl, and rather friable or fhort than plaflic in the interior parts of it. I BEAT the whole of it w^th a little water to its former confiftence ; and with this mortar and clean new bricks, I built a wall eighteen inches fquare and half a brick in thicknefs,^ in a workman-like manner. On the fame day I made mortar of the fame kind and quanrities of frefh chalk lime and fand, tempered in the fame manner; and I built a wall with it, like the former, near it, and expofed equally to the weather. I L 39 J I EXAMINED the mortar In the joints of thefe walls every fortnight, by picking it with a pointed knife, and could perceive a very confider.ible difference in the hardnefs of them ; the mortar which was ufed frelh being invariably the hardeft* At the expiration of twelve months, in pulling thefe walls to pieces, and by feveral trials of the force neceflary to break the cement and feparate the bricks, I found the mortar which had been ufed quite frefli, to be harder and to refill fra£lure and the fepa- rationof it from the bricks, in a much greater degree than the other fpecimen. Considering that mortar expofed in the foregoing manner, muft imbibe fome acidu- lous gas, though not fo much, perhaps, as th^ . dry and fpongy lumps of lime drink in, dur- ing the fame time ; that the additional quan- tity of water necelTary in beating it up the^ fecond time, muft have introduced more oF the like matter, as all native waters contain fome quantity of it ; that the frefh expofure in the laft mentioned agitation of the mortar . muft have contributed fomething to the fame D 4 effed? [ 40 ] cfTed; and laflly that the event of this expe* rlment coincided with the notions ah'eady de- rived from others ; I concluded that mortar grows worfe every hour that it is kept be- fore it is ufed in building, and that we may reckon as another caufe of the badnefs of common mortar, that the workmen make too much at once, and falfly imagine that it is not the worfe but better for being kept fome time. Having in confequence of thefe obferva- tions had a great deal of converfation with workmen on this fubjeft, I could perceive the origin of this error. Some portions of every kind of lime ufed in this country, do not flake freely, by rea- fon of their not being fufficiently burned, or of the admixture of gypfeous or argil- laceous matter; and thefe, like marie, flake in time, though not fo quickly as the purer lime. , The plaiflerers, who ufe a finer kind of mortar made of fand and lime, obferve that their plaifter or fhucco blifters, when it con- tains [ 41 ] tains fiiiall bits of unflaked lime; and as their purpofe is to work their flu ceo to a fmooth furface, and to fecure it from cracking, or any fiich roughnefs as would be occafioned by the flaking or mouldering of bits of calca- reous matter in the face of it ; and as the hard- nefs of the flucco is not their chief objed; they very properly keep their mortar a confi- derable time before they ufe it, to the end that the bits of imperfed lime, which pafled through the Ikreen, may have time to flake thoroughly. It appears to me that there is another rea^- - fon, which the workmen do not notice, for their procefs. Lime foon imbibes fo much acidulous gas from the air, as to be in- creafed in bulk, and in weight beyond the half of its former quantity; and as ftucco for infide work, for the fake of a fine grain and even furface, mufl: have a greater quan- tity of lime in its compofition, than is ne- cefTary for cementing the grains of fand to- gether ; the incruftation would, by the accefs of acidulous gas after it is laid on, be apt to fwell and chip and lofe the even furface, if the lime were frefli when it is ufed in thi^ excefiive [ 4^ ] cxceffivc quantity. But this inconvenience is obviated by their procefles, in which the lime, whether flaked into water or other- wife, imbibes a confiderable quantity of the gas, and is therefore the lefs apt to blifter or fwell, after the flucco is laid on. The builders confidering the plaifterers mortar or ftucco as a finer and better kind of mortar, think it not amifs to imitate them in thofe particulars which are not attended with any expence, and efpecially in the practice of flaking a great deal of lime at once, and of keeping the mortar made fome time ; and they do not feem to know, that fuch meafures prevent the mortar from ever acquiring that degree of hardnefs in which the perfedion of mortar truly confifls. SECTION [ 43 ] SECTION VII. Of the Depravation of Mortar hy the common Method of ufng the Water; and of the life of Lime water. FINDING byreafonand experience, the advantage of totally expelling the gas, and preventing the return of it to lime or even to mortar before it is nfed ; and knowing that common water, which is em- ployed in great quantities, firfl: in flaking lime, and then in making mortar, contains a great deal of the noxious gas ; it occured to me that the vulgar procefs of making mortar is in this frefh inftance injudicious, as it tends to injure materials otherv/ife good. They flake lime in fuch a manner that almofl" the whole of the water is evaporated, and contributes nothing to the mortar, except fo far as it depofltes its gas in the lime and injures it ; and then the flaked dry lime and the fand, require more water to make them into [ 44 J liito mortar. I have found tlie quantity of water ufed for both thefe purpofes, to be twice the weight of the lime^ at the leafl. The quantities of acidulous gas known to be contained in the waters commonly ufed in mak- ing mortar, muft greatly debafethe lime which is thus expofed to double its weight of fuch water; and upon thefe grounds T was affured, a priori, that it would be a confiderable im- proYement in mortar, to ufe no water in it except what has been previoufly freed from acidulous gas. This is done in making lime-water; and the ufe of lime water appeared advantageous in another point of view. One feven hun- dredth part of lime water being lime, accord- ing to the experiments of Mr. Brandt which I find to be true; and this lime being in- troduced in a ftate of folution which favours the cryftalination of it between the grains of land, affiffcs in cementing them together by the utmoft attradive forces of its parts, if my notions of the polarity of thefe parts be true. [ 45 ] I MADE divers experiments to try the prac^ -tical validity of this reafoning, and found it to be trye : for on comparing fpe.cimens of mortar made v/iih my befl lime flaked with river water, and land and water, and fpread on tiles foaked in water, with other fpeci- mens made with the fame proportions of lime llaked with lime water and fand and lioie water, and fpread on tiles previoufly foaked in lime water, the latter, 4t every age of them, were fenfibly harder, and they adhered to .the tiles better thaii the former. I muft ob- ferve however, that fach diftindiions cannot eafily be made, except by thofe who have a great deal of experience in thefe trials and comparifons. On repeated examinations of theip and my other fpecimens, I was highly en.- couraged ill my purfuit ; for thofe made with lime water were better near the furface than any I had ever made ; and I had good reafons to be perfuaded that the extraordinary indur jation would proceed in time through the lyhole mafs. SECTION [ 46 ] SECTION VIIL Experiments made with a View to approximate the heji Proportions of luime Sand and Water ^ for Mortar, IN reading over my notes, and examining the fpecimens of mortar which I had hi- therto made, I perceived that thofe were the heft which being made with common frefh lime, or with well burned lime, contained the leaft of it ; that is one ounce of lime in fix or more of fand ; and finding this quantity of lime to be much lefs than is ufed in the common way of making mortar ; and fufpeding that as a wall may be the weaker for its containing too much mortar, which widens the joints, lb mortar may be weakened by the introduc- tion of more lime than is neceflary to cement the grains of fand together ; I thought an- other caufe of the defed of common mortar opened to my view ; and that it was advifable to determine by experiment, what is the beft prop or- r 47 ] proportion of lime to fancl, in making mortar in which lime water is ufed. I MADE five parcels of mortar with my heft flone lime re.cently flaked with lime water, and with the coarfe Thames fand, in the following proportions by weight. I. Slaked lime — — . | Sand — ^ — Lime water, q. f. 2. Slaked lime — Sand Lime water, q. f. J* Slaked lime — 4 Sand — — - ^ Lime water, q. f. 4, Slaked lime — — . i Sand — — T Lime water, q. f. 5. Slaked, •[ 43 ] 5- Slaked lime r~ ^ — % Sand — — 8 Lime water, q. f. This latter fpecimen was not fufficiently plaftic for common ule ; or as the workmen exprefs themfelves, it was too fhort. I fur- ther obferved that the quantity qf water rei- iquired to make mortar to the proper temper, •is greater as the quantity of lime is greater relatively to the quantity of fand. I SPREAD thefe on tiles in the month of June, and expofed them to the air and the fun, which then was very hot, As my former experience taught me to expect that fome of thefe, in hafly drying, would crack confiderably ; and as mortar, in building, is not liable to dry fo quickly as thefe fpecimens; in order to render the in- ferences from thefe experiments the more general, I made five other parcels of mortar in the fame manner and expofed them in the fame way, in every refpeft, except that the dire61: rays of the fun could not fail on them 05 [ 49 ] or heat the pavement on which they iliood. In three days I found this rieceffary, for the firft of thofe which fl:ood expofed to the fun cracked confiderably, the fecond cracked lefs, the third fhewed three or four very flender fifliires vifible only on a very clofe infpedtion^ the fourth and fifth fhewed no cracks at this time, nor in a month after^ wards, when the fiffures of the others were conliderably enlarged* Of the fpecimens kept in the fhade and examined on the third dav like the former the firfl was cracked in divers parts, the fe- cond fhewed two or three very flender cracks, the refl were not cracked in the leafl, and never cracked afterwards, although I was forced to remove them to the place where the others flood* Thus it appeared in a Very fhort time that an excefs of lime diipofes mortar to crack, and confequentiy injures it ; that the highefl proportion of lime to fuch fandj which may be ufed without incurring this inconvenience, depends on the circumflances in which the mortar is to be expofed ; that no more than E one [ so } one part of lime to feven of coarfe land ought to be ufed in mortar which is to dry quickiy ; and lefs lime may not be ufed, be- caufe it does not render the mafs fufficiently plaftic for building or incruftation ; and that if a greater proportion of lime to fuch fand in^p'roves the mortar in any refpe£l, it is to be ufed only where the mortar cannot dry fo quickly as it did in the fpecimens expofed to the fun. In the courfeof nine months I clearly per- ceived that thofe fpecimens which flood in the (hade for the firft three days, were harder, and better in other refpeds, than thofe which were fuddenly expofed to the fun, the comparifon being made between the fpecimens which contained the fame pro- portions of lime, and which cracked the leaft, or not at all : and of all the fpecimens, tliofe were the beft which contained one part of lime in feven of the fand : for thofe which contained lefs lime, and were too fliort whilft frefh, were more eafily cut and broke, and were pervious to water ; and thofe which contained more lime, although they were clofer in the grain, did not harden fo [ SI J fd foon Or to fo great a degree, even wlien tliey efcaped cracking by lying in the fhade to dry (lowly. I THEREFORE Concluded that hafly drying injures mortar made in any proportions of fuch fand and the heft lime ; and thi^t the beft proportion is one of lirnie in feven of fand, whether the mortar is to be quickly dried or not; I MUST obferve however th^t thefe conclu- fions were made rather with a view to my future experiments, in which an approxima- tion to the befl proportions of lime and fand and the beft treatment of the mortar would fave a great deal of trouble, than to any ge- neral and invariable rule for making mortar. i RESERVED it to be mentioned in this place, that I fet apart four ounces of each of the foregoing fpecimens of mortar, and Ipread thefe portions feverally on plates of thin window glafs, to the thidknefs of a jquarter of an inch or thereabouts; and I noted the weight of each plate with its fpe- limen of mortar recently made, E 2 These [ 5^ ] These being equally expofed ta the fan aftd weighed at different periods were found to lofe weight in equal times nearly in the proportion of the quantity of lime or of wa- ter uled in makins: them ; and the fmalleft lofs of weight when the fpecimens were per- fedly dry and conliderably hardened, was one- tenth of the weight of the iame fpeci- mens recently made. In many former experiments I had ob- ferved, but referved it to be mentioned in this place, that mortar which fets without cracking, whether this be owing to the due proportion of fand, or to the flow exhalation of the water from mortar containing lefs fand ; never cracks afterwards, whatever other faults it may have: the fpecimens men- tioned in this fedion, after a trial of eighteen months afforded the fame obfervation. By the fetting of mortar, I underifand that folidity which it acquires by mere drying, and which differs widely from the induration that takes place in time by other means which we fhall prefently coniider. Seeing [ 53 ] SiEEiNG then that the quantity of water in moirtar is as the quantity of lime, that the fifiuires happen only in the drying or fetting, thaG the danger of cracking is greater, not merrely as the quantity of water is greater relattiyely to the fand, nor merely as the wa- ter is more expeditioufly exhaled, hut, in a rate compounded of thefe ; I inferred' that mortar which is to be ufed where it mufl: dry quickly, oi]ght to be made as flift'as the pur|pofe will admit, that is, with the fmallefl: pradilicable quantity of water ; and that mor- tar will not crack, although the lime be iifedl in exceffive quantity, provided it be madie ftifFer or to a thicker conhflence than mortar ufually is. T'his inference was afterwards found to be true : for fpecimens made thus with one part of I'iime and only hx of the fand, and others madie with greater proportions of lime, but as ftnff as they could be ufed, did not crack, in amy expofure ; but they had faults which will be hereafter noticeg, E3 SECTION f 54 ] SECTION IX. Theory' of the Induration dependent on the Pro- forttons of Lime and Sand in Mortar, and dbfervations on the had EfeSfs of the viJ^ar Proportions of thefe. IT is fufficiently known that the aggre- gation of calcareous bodies, which burn to Ume, or are chiefly compofed of the mat- ter of lime, is much weaker than that of the quartofe; infomuch that the freei w^hich eafily cuts all calcareous ftones or fpars, is as eafily cut by the filiceous ; and all ftones, or powders which are chofen for cutting or grinding fteel, are found to have this eife where the mortar was heated to about an hundred of Farenheit for fix hours and then to an hundred and fif- ty for four hours more, at the expiration of which it was foHd and perfectly dry* The next day I placed it in the open air, expofed to the fun, and the weather, which was dry and warm for a confiderable time, afterwards. On comparing thefe two laft at the expi- ration of feven months, and again after fix months more, I could eafily perceive that the t 67 ] the latter was inferior to the former; for k was much more eafily cut and fcaled from the tile and broken^ Experiment 7. With mortar made, the day after I had made the former, of the fame materials and in the fame manner ; and with new bricks, which I had heated almoft to rednefs and fufFered to cool to the temperature of my hands ; I brilkly ereded a little wall half a brick thick, on a ftone bench raifed for the purpofc and fully expofed to the weather. Experiment 8. On the fame day and with the like mortar^ and with cold new bricks previoufly foaked in lime water, I ereded another wall, equal to the former in dimenfions, and placed in the fame manner on a ftone bench in the open air. AfteiI nine months, in pulling tliefe walls to pieces and in divers comparifons of the cement of them, I found that the latter cement adhered better to the bricks and was harder [ 68 J harder than the former, infomuch, that I had not a doubt about it. Experiment 9. . In a few days after I had made the expe- riment with the warm bricks, I confidered the walls ereded in variable weather, and the fence walls which are wetted frequently and deeply whilft new, by rain, or by moifture from the ground, and as often dried quickly ; and 1 was defirous to learn the effed of fuch alterations of wetting and drying. I THEREFORE fpread mortar, made like thofe parcels lately mehtioned, on a large tile foaked in lime water, and as often as it had dried, in fair weather, and generally at the interval of three days, I wetted it with rain water. In the courfe of nine months I found it was much lefs indurated than the fpecimen made in the fame manner, and de- fended from the rain : it moreover grew green by ■'means of a vegetation which took place on the furface of it, and which" thrived the more as the mortar was frequently wetted, or the tile longer fufFered to lie flat on the ftone bench already mentioned. [ 69 ] I HAD often obferved fuch a vegetation on mortar which I had made a few months be- fore, efpecially when, in the fummer feafon, I laid the tiles flat on the wooden border of a dufl-hole, or when, for want of room to preferve the fpecimens in, I piled many of them together in a damp corner on the pave- ment : I likewife faw that where the vege- tation took place, the induration did not pro- ceed as it does elfewhere : on the contrary, femi-indurated mortar foftened there. All thefe being confidered, I w^as fatisfied that frequent wetting or conftant moifture, together with expofure to air, injure mortar in a great degree, if it be not perfectly indu- rated by great age before it is expofed to fuch trials ; and that the vegetation depends chiefly on moifturc. Experiment io. By the kind of analyfls mentioned in the tenth fedion, I repeatedly examined the proportion of acidulous gas to the lime, in the hardeft of the old cements which I had collected ; and finding it in the beft of them to be, at the loweft, in the proportion of three F3 to [ 7° J to five, I rate the quantity of acidulous gas im^ bibed by good mortar, during the induration of it, at fixty pounds at leaft, for every huri- dred pounds of lime. Experiment ii. Such mortar as that of the firft experiment of this fedion was formed into (lender pieces, each an inch broad, a quarter of an inch thick, and three inches in length. Thefe were placed in an airy paffage, fheltered frorr^ the fun and rajn, and were turned as foon as they could bear it without danger pf cracking • they were then fet upright and fully expofed on all fides to the air. On the fourth day I flid four of the pieces entire into a fmall wide-necked glafs retort, which I fet deep in a fand bath, with its nozzle immerfed in quickfilver, which flood cool whilft the charge was gradually heated, in the courfe of forty-eight hours, to about feventy-five of Farenheit, which is under the temperature of incruftations of this kind ex- pofed to the fun in fummer ; and in the courfe of forty eight-hours more was flowly heated tp about an hundred of Farenheit, to which [ 7' ] which degree incruftations are frequently heated by the fun in fvimmer. As the retort cooled I admitted the neceffary quantity of air, and then left it, with the nozzle im- merfed deeply in the mercury, during three months. I then Aid the pieces gently out of the retort, after having wiped away a few drops of water which adhered to the veffel in their way ; and immediately made the com- parifon which 1 fliall prefently mention. Close to the retort, and In a fituation where the heat was equal to that defcribed/ or nearly fo, I placed four other of the pieces aboye defcribed, on the fourth day after they were made : I encompaffed them with the iiind, but fecured a free accefs and even a cir- culation of air to them. When the fand bath was cooled, I put thefe pieces, which were thus perfedly dried, into a bottle which I flopped clofely in the manner heretofore defcribed* On the leventh day after the pieces were made, on the twenty-firft, and at the expi- ration of three months, I examined four pieces taken from different quarters of the F 4 remaining [ 7^ ] remaining parcel, and fo.iind the quantity of acidulous gas which they yielded, to corre- fpond with the degree of induration and the depth to which it had advanced in them re^ fpeilively. On corn paring and exam/ming the pieces dried in the retort and kept three months in it ; the pieces dried in the f^me heat and freely expofed to air during four days, but afterwards kept in a clofe veflel; and the pieces which clried and hardened in the free air, without being heated ; I found that the firfl were frjable in comparlfon with the fecond, and the laft were b^ much the hardeft and befl, As the fecond tenth and eleventh experi- ments, together with obfervations formerly made, fhew that the induration peculiar to mortar, is not caufed by exliccation ; that it is greater, as the calcareous rnatter of cements approaches nearer to be fa tu rated with acidu- lous gas; that it is retarded or prevented, as the acceffion of acidulous gas is interrupted or obviated ; we may conclude that this mat- |:er is a principal agent in the induration of cglca^ [ 73 ] calcareous cemeiUs ar.d indifpenfibly necef- fary to it. By obfervations formerly made, but efpe- QiciWy by the comparifon of the fifth and eight experiments of this fedion with the fixth and feveiith, I learned that hafty dry- ing prevents good mortar from ever ac- quiring the hardnefs which it otherwife would have ; and that the more flowly the proper water of the mortar is exhaled or abforbed fi'om it, in incruftations or brick- work, the more perfefft will be the indura- tion of it. By the firft third and ninth experiments of this fedion compared with the fourth, fifth Jind others, and by obfervations which led me to make thefe experiments ; I difcovered that mortar which is not fuffered to dry, or which is fupplied with moifture as faft as its proper water exhales, does not harden, pr hardens only to a fmall degree by any ^cceffion of acidulous gas. The fourth experiment indicates that mor- tar, whofe lime has not yet imbibed its com- plement plement of acidulous gas, although the mafs be confiderably hardened, is liable to be in- jured by foaking in water, if it be pervious to water fo freely as thefe thin pieces were. All thefe experiments and obfervations confpire to point out the circumftances in which mortar becomes indurated the fooneO: and in the highefl: degree, and operates moft efFe^tually as a cement. To this end it muft be fufFered to dry gently and fet ; the ex- ikcation muft be effeded by temperate air and not accelerated by the heat of the fun or fire : It muft not be wetted foon after it fets ; and afterwards it ought to be proteded from wet as much as poffible, until it is compleatly indurated: the entry of acidulous gas muft be prevented as much as poffible, un- til the mortar is finally placed and quiefcent : and then it mufl be as freely expofed to the open air as the work will admit, in order to fupply acidulous gas, and enable it fooner to fuuain the trials to which mortar is expofed in cementious buildings and Incruflations. From thefe confideratlons we learn other caufes, befides thofe already mentioned, of the fpeedy ruin of ov)r niiiodern buildings. . The [ 75 ] The mortar made with bad lime and a great excefs of it, and debafed in watering and long expofure, is ufed w^ith drj bricks and not un frequently with warm ones. Thefe immediately imbibe or diffipate the water and not only induce the defe£l above no-^ ticed, but, as the cement approaches nearer to be dry, whjlfl: it is ftill liable to be dif- turbed by the percuffions of the workmen, render it more nearly equivalent to a mix- ture of fand and powdered chalk. But to make ftrong work, the bricks ought to be foaked in lime water, and freed from the duft, which in common bricklay- ing, intercedes the brick and mortar in many parts. By this method the bricks would be rendered clofer and harder ; the ce- ment, by fetting flowly, would admit the motion which the bricks receive when the . workman dreffes them, without being im^ paired; and it would adhere and indurate more perfedly : the fame advantages would attend the foaking of bibulous ftones in lime water, and the ufe of grout; provided this were made with good hrne fand and lime water. In [ 76 ] In plaiflering, the workmen always brufli away the daft and wet the wall on which they are to lay the cement, becaufe it will not otherwife adhere. From what has been already faid it is manifeft that this ought to be done with lime water, and re- peated as long as the wall is thirfty. To perceive more clearly how much our {light buildings are weakened by the agita- tions and percuffions to which they are ex- pofed, firft in erecting the walls and fettling the timbers, and then in driv- ing thofe wedges to which they faften the wainfcots corniflies and other ornaments, we muft obferve that the acceflion of acidu- lous gas to mortar, was found to contribute nothing to the ftrength of it, when it entered the compofition before it was finally fixed in a quiefcent ftate : and a little experience is Sufficient to teach us, that the fame mat- ter which affifts in the induration of mortar, never ferves to repair the fiflures, or fo- lutioii of continuity between the bricks and cement, which happen after it is fet. When mortar is fet, and before it is in- durated, it may eafily be ferved from the bricks [ 77 ] bricks and crumbled; and for want of foft- nefs it cannot bend into the fiffures, or re- fume its former condition in any time. Therefore by heavy blows, and in wedging, ♦ our walls muft be greatly weakened ; and the more, as the houfes are flight, quickly built, and haftily finiflied. SECTION [ 78 i SECTION XII. "Experiments fiewlng the hejl Kinds and Mixtures of Sand ^ and the heji Method of ufng the Lime Water, in making Mortar* PURSUING the analogy intimated in the ninth fe£tion, I thought that as large ftones with Carvilinear faces, bedded in com- mon mortar, do not form fo flrong a wall as they may when their interftices are filled with fitting ftones together with the due quantity of mortar; fo mortar made with fand, whofe grains come near to be equal in fize and globular, cannot be fo ftrong at any period of induration^ as that which is made with the fame mixed with as much fine fand as can eafily be received in its in- terftices, in order that the lime may ce- ment the grains by the greater number and extent of contiguous furfaces. By this no- tion I was excited to make provifion for a new feries of experiments. I CLEANSED a large quantity of the Thames fand, by wafhing it in ftreaming v/ater, and forted [ 79 ] forted it into three parcels : the coarfeft, which I call the rubble, confifted of fmall pebbles, fragments of weathered Ihells, and grains of fand of divers fizes, which in waihing had pafled through a fieve whofe apertures were one eighth, of an inch fquare', but could not pafs through a brafs wired fieve, whofe meflies were one llxteenth of an inch fquare, or rather larger: the next parcel, which I called fine fand, confifted of grains of divers (izes, which in wafhing paf- fed through a finer fieve whofe mefhes were one thirty-fecond of an inch fquare : the third parcel confifted of grains the largefl of which were wafhed through the coarfeft fieve, and the fmallefl were retained, in wafhing, on the fine fieve : this I call coarfe land. It is to be obferved that the fand which can pafs through a fieve, in wafhing, is con- fiderably finer than that which may be fifted through the fame fieve, when it is dry. Having dried thefe parcels on a fand plate, and provided a narrow mouthed glafs bottle capable of holding about two ounces troy of water, and a cylindrical glafs vefi'el which con- tained t 8° 3 tained twelve of thefe meafures, I found by repeated trials, that the large veflel, charged to the brim with my rubble, might be made to hold fomewhat more than one additional meafure of it, when the rubble was well packed, by ftriklng the bottom of the veflel frequently againft the table perpendicularly* Charging the fame veffel with coarfe fand, I could by the fame treatment make it hold two thirds of the thirteenth meafure: and twelve meafures of fine fand were fo far contradled in this motion of the vellel, that it could hold one meafure and one fourth more, or thirteen and one fourth in all. After noting how far the interfticial fpaces in each fized fand can be leffened by packing, I ufed water to fhevv what propor- tion thefe bear to the folids, in thefe diffe- rent fands. I found that the thirteen mea- fures of rubble which I flowed into the o-lafs cylinder, could take in five meafures of water, without any increafe of bulk ; or rather with a flriking decreafe of bulk : the twelve meafures and two thirds of ftowed coarfe fand, imbibed four and one half of water, and yet decreafed fenfibly in bulk : the thirteen mvafures [ 8' ] hleafures and one fourth of fine fand packedj could drink in only four meafures of water i but the diminution of bulk was more confider- able than in either of the former ; for the fand and water together meafured lefs by one fe- ventieth than the packed fand alone* When fand was poured into the glafs Cylinder until it was filled, and water was added before the fand was packed, by a flight agitation of the veffel the fand contracted in a much greater degree than is above exprefled. Upon the whole it feemed that water, by poifing the grains, facilitates their Aiding on each other to fit well and fill the fpaces. • Until 1 had made thefe experiments I did not well underftand, how the beating of new mortar makes it much wetter, and more plaflic withal, than it can be made with the fame proportions of water and follds, by mere mixture. I now perceive that beating produces this efftCt by elofing the interftices of the fand, and rendering a fmall quantity of ' lime pafte as effedlual towards filling theni and holding the grains together to form a G plaftic [ 82 ] plaftic mafs, as a greater quantity is, in fand whofe grains cannot fit each other fo well. Seeing that the interfticial fpaces in fand are fo greatly leffened by wetting it, 1 judged it expedient, for this reafon alone, to expend all the water I fhould henceforward ufe in making mortar, in wetting the fand com- pleatly. I afterwards obferved other advan- tages arifing from this pradice : for in filling the fpaces with the fluid, the air is eafily ex- pelled, and the lime equably difFufed in them by a little beating : but when the water is added to a mixture of lime powder and fand, the air is entangled in the lime pafte, and cannot, without a great deal of beating, be totally prefied out of the plaftic mafs : I llkewife found, that as an excefs of water is injurious in mortar, this is an excellent me- thod of regulating the quantity of water; for the portion of lime water which fills the fpaces in fand, and can be held by capillary attraction in a flat heap of it, is precifely the quantity which makes well tempered mortar with one part of the beft flaked lime and feven of the beft fand. As t 83 J As I found fome difficulty in expelling tlie air bubbles out of the fand wetted in my deep cylindrical meafure, even when I flirred up the mafs wath a {lender inflrument, I con- cluded that the fpaces in fand are rather in a higher proportion to the folid fubftance of it, than they appeared in thefe trials : fo that we may fay they are at leaft one third and more of any meafure of the fine fand, greater in coarfe fand, and greateil: in the nibble. Suf-^ pe(£ting on another ground that thefe experi- ments did not Ihew the whole of the fpaces in fand, becaufe water tends to infinuate itfelf between the contiguous faces of the grains, and confequently to remove them afunder, even whilffc it arranges them ; I attempted to afcertain the proportion of thefe fpaces to the folids, by another method founded on this fuppofition, that the meafured portion of fand which weighs the moft, has the fmalleft quantity of interfticial fpace* By the experiment, I found that a Well packed meafure of the rubble weighed twen- ty ounces three pennyweights : the like meafure of the coarfe fand packed, weighed twenty one ounces eighteen pennyweights i G % and t 84 ] ?ind the fame quantity, by meafure, of the fine fand, weighed twenty three ounces two pennyweights and twelve grains. This trial correfponds fufficiently with the former in (hewing, that the fum of the fpaces in the rubble,is much greater than that of the coarfe fand, and that the fpaces in this are larger in the fum, than thofe of fine fand. In order to learn whether this proportion is maintained in all kinds of fand, I tried by water and by weight in the foregoing man- ner, a great number of fands ufed in London ; fuch as the coarfeft glafs- grinder's fand, Hampftead-fand, Lynn- fand, fine houfe-fand The refult of thefe experiments taught me that the fpaces are always fmaller as the fand is finer, provided the comparifon be made between the forted fine part and the coarfeft part of any kind of fand : but this does not' hold true in the comparifon of fine fand and coarfe land of different diftrias. On [ 85 ] On examining the feveral fpecimens of fand with a lens, I perceived that, in fome, the grains, however different in figure, were bounded by flat faces meeting each other m angles ; whilft in others, the faces were ge- nerally rounded, and the figure fuch as the foregoing grains would be reduced to by grinding off their angles. The firft kind I call fliarp fand, the other round fand. Then taking into confideration the meafurement already defcribed, together with the fharpnefs or roundnefs of the fand, I found that the fpaces are, in different kinds of fand, as the fize and roundnefs of them compounded ; but they do not appear to be fmaller in any kind of fand that I have feen, than in our fine parcel of Thames fand ; which I think is owing to its being (harper than any of the finer fands which J had compared k with. The meafure which contained twenty-three ounces two penny- weights twelve grains of the fine Thames fand, contained only twenty-two ounces ten pennyweights of the Lynn fand, which is a, great deal finer, but rounder. Having thus found the kind of fand which, by reafon of the fize and figure of the G 3 grains grains, ha» the fmallefl interfticial fpace ; I pext endeavoured to afcertain the mixture of coarfe and fine fand, which leffens this fpace in the greateft degree, which theref&i'e re- quires the lefs lime to cement the grains to^ gether, and for the reafons already mentioned, f romifes to make the hardeft and moil dur- able cement. I FOUND that nhie meafures of the ihingle, and nine meafures of the fine fand, both well packed, meafured when mixed and flowed ciofely fixteen meafures and one-eighth : that eighteen meafures of the flilngle and nine of the fine fand tried in the fame way, mea- fured twenty-four: and that on mixing the fhingle and fine fand in various propor- tions, nine meafures of fhingle took, into its interflices, one meafure and one half of the fine fand, without any increafe of bulk, I NEXT learned that nine meafures of the coarfe fand and nine of the fine, meafured in the like manner feventeen and a half : that eighteen fuch meafures of coarfe fand well mixed with nine of the fine fand, meafured twenty-fix ; and that on rnixing thefe fands [ 8; j In various proportions, eighteen meafures of the coarfe fand took into its interftices one meafure of the fine fand, without any increafe of bulk. Lastly I found that eighteen fuch mea- fures of the coarfe fand and nine of Lynn fand, which is much finer grained than the foregoing, meafured twenty-four when well mixed and flowed : and that on mixing them in various other proportions, nine meafures of the coarfe fand took into its interflices one and a half of the Lynn fand. By thefe and a variety of fimilar experi- ments made on different fands, I found that the quantity of fine fand taken into the inter- ftices of a coarfe fand, was the greater with- out increafe of bulk, as the grains of the coarfe differed more from thofe of the fine in bulk, provided the diameters of the grains of coarfe fand did not in general exceed thofe of the fine, in a proportion greater than five to one; that the greateft quantity of fine fand, which could be taken into the inter- fticesof coarfe fand, was one-fixth of the tulk of the coarfe fand ; and that in general the G 4 mixture [ 88 J yni^re of fix meafures of coarfe fand witk, one of the fineft fand, reduced the fum of the interfticial fpaces to nearly qne half of the quantity of them in coarfe only, or in iine Th^arpes fand or rubbje only. Instructed by thefe obfervations I prq- f eeded to the following experiments, in order to learn the advantages or defeds attending each kind of fand, ^nd how far my expefta- tions from the art of l^flening the fpaces^ ^ere well founded, I MADE feveral parcels of mortar with my chalk lime lime water and rubble in different proportions ; the quantity of lime being in one a fourth of that of the rubble, in another only one-feventh, and in the others interme- diate : I made other parcels of mortar with my chalk Ijme, lime water, and the coarfe fand ; and others with this lime, lime-water and the fine Thames fand, in the laft mem tioned proportions. I NEXT made a great variety of fpecimens of mortar ; fome of which confifted of rub- ble and coarfe fand mixed in different pro- portions^ [ 89 ] portions, wetted with lime-water, and blended with one-fourth or one-feventh or intermediate quantities of lime : others were compofed of fimilar mixtures of rubble and fine fand with lime and lime water ; and others conlifted of rubble coarfe fand and fine fand mixed in different proportions, wetted with hme water, and beat up with the different quantities of lime lately mentioned. I SPREAD a part of each of thefe fpecimens of mortar, as foon as it was made, on a tile foaked in lime water, half an inch thick in fome places, and much thinner in others : I placed the remainder of it, formed into oblong pieces of about an inch diameter, on the part of the tile which was not covered with mor* tar; and I fet all the tiles numerically marked, in the fituation formerly defc ibed, where they were equally expofed to the wea- ther : this was done in May, 1777: dur- ing the fucceeding twelve months I examined each fpecimen, and noted my obfervations, the moft ufeful of which I fhall endeavour to relate in a few words. The [ 9° ] The fpecimens containing rubble and lime mixed in any proportion greater than five.to one, were not fat enough, when frefh, to be con- veniently ufed in building or fluccoing : but none of them, not excepting thofe which contained the greater quantities of lime, cracked in drying. Thofe which had the fmaller quantities of lime in them, were very rough on the furface, coarfe in the grain, fpongy, and eafily broken : they fhewed a defed of lime, becaufe thofe which con- tained more lime were not fo bad in thefe re- fpects. By all of them it appeared that whenever fuch rubble muft be ufed, for want of fand or finer gravel, the lime mixed with it muft not be lefs than one-fifth of the quan^ •tity of rubble. Qp the fpecimens confifting of coarfe fand •and lime, thofe which had the fmaller quan- tities of lime were too lliort for common ufe, and could not be made to aflume a clofe and Imooth furface, whilft frefli ; but in drying and hardening, they were in every refpeft preferable to the cements made with rubble and lime, in the fame proportions : and of the fame fpecimens, thofe were the befi: which contained [ 91 ] contained one part of lime in five of fand ; the others containing lefs Hme being faulty like thofe made with rubble, and thofe in which the lime was mixed in much greater quantity, having the faults often obferved to attend the excefs of lime, The fpecimens which confifled of fine fand and lime, were in general better than the foregoing : and that particularly which contained one of lime in fix and an half of fand, was in all refpeds much better than thofe made with the fame or any other quan- tities of rubble and lime, or coarfe fand and lime. The fpecimen which was formed with feven parts of fine fand, and one of lime was not fo compad and hard as that laft mentioned. The comparifon of thefe two fhewed that feven of fand are too much for one part of lime, when the fand is fine and unmixed with coarfe grains. The fpecimen made with four parts of fine fand, and one of lime had the noted faults attending the excefs of lime ; for it cracked in drying, and was fenfibly injured in the winter, by thofe alternations of drying, wetting, freezing, md thawing, formerly noticed. On I 9^' ] On jiivers comparifons of thofe portion of mortar made of fine fand and lime, with the former, I was perfuaded that a better ce- ment can be compofed with fuch fand as I call fine, than with a coarfer fand, whofe grains are all larger than any of thofe in my fine fand ; provided the coarfer fand be not much (harper than all that I have yet feen, If my experiments had been made in flow fucceifion, this lall: obfervation would have "Jed me to imagine that mortar will be fgund the better as the fajid is finer. Of the obfervations made on the parcels of mortar confiding of mixed fands and lime, thofe which follow are the rnoil pev» tinent to our prefent encjuiry, The fpecimens made with mixtures of rubble, coarfe fand and different quanti- ties of lime, refembled thofe made with rubble and lime in fimilar proportions, when the rubble was predominant; and 'refembled thofe made with coarfe fand and lime, in fimilar proportions, when the coarfe fand was predominant ; and I could perceive no [ 93 ] no advantage derived from the mixture of rubble anti' coarfe fand, except that the ce- ment was fomewhat better as the quantity of rubble was lefs, relatively to the quantity of fand and lime : but none of thefe fpecimens were in any refped fo good as thofe made with fine fand only. Of the fpecimens made with rubble and fine fand, that was the beft in which the fine fand was twice the quantity of the rubble. But I could not perceive that any of thefe fpeci- mens were preferable to thofe made with the like quantities of fine fand and lime ; or that any confiderable advantage is gained by the mixture of rubble and fine fand. Of the fpecimens made of coarfe fand fine fand and lime, thofe were manifeftly the beft, which confifted of four parts of coarfe fand, three of fine, and one part or a little more of lime : for, whilft frefli, they were more plaftic than the others, and were eafily made to afiumeafmooth furface; they were not difpofed to crack in this method of drying ; they were not at all injured by wet or freezing^jr thaw- ing ; they were pretty clofe in the grain ; and i 94 ] they grew fo hard, in the courfe of nine or ten months, as to refift the chizel, d'f any force tending to break the oblong pieces, much more powerfully than any of the fpecimens lately mentioned. 1 noted them as the befl fpecimens of mortar that I had ever made; and one part of lime, in four of coarfe, and three of fine fand, to be a better proportion than any other of the fands and lime, for incruflations. Of the various fpecimens of mortar made with mixtures of the rubble, coarfe fand and fine fand, thofe were the bell:, in which the fine fand was equal or nearly equal in quantity to the rubble and coarfe fand ; in which the rubble was not much more than one feventh part of the quantity of both fands ; and in which the weight of the lime was one feventh of the weight of the fand and rubble, or a httle more : But thefe fpecimens, when frefh, were lefs plaflic, and lefs capable of affuming a fmooth furface under the trowel, as the quan- tity of rubble was greater ; and I could not find they were preferable in any particular to thofe refpedively which were made with fimilar quantities of lime and the mixtures of coarfe and fine fand lately commended. Upon [ 95 ] t Upon the ftrideft comparifon, I concluded, that one part of rubble in three of coarfe and three of fine fand, makes as good mortar with lime, as can be made with the fand and lime without rubb'e, for any purpofe which does not require a finer cement ; but there is no advantage gained by theufe of rubble where the coarfe and fine fand can be had equally cheap, \inlefs a rough furface be required. In ftuccoing walls the rubble promifed to be ufeful in pointing and in the firft coat ; becaufe a roughnefs of this coat makes the finer exterior coat adhere more firmly. In the review of all thefe fpeclmens it ap- peared, that the quantity of lime, which forms a mafs fomewhat plaftic with fand and water, is the fmalleft quantity neceflary for making the heft mortar which fuch fand can afibrd ; and that any further quantity of lime is ufe- lefs in the coarfer fands, and injurious in the finer : that the neceffary plafticity is induced by the fmaller quantities of lime, as the in- terftices of the fand are fmaller in the fum, and as the grains fit each other the better in confequence of the due mixture of coarfe and fine E 96 ] fine fands : but that the lefleningof the intfer* fticial fpaces, by the mixture of fine fand with the coarfe, does not enable us to leflen the quantity of lime fo far as might be ex- pelled in confequence of our notions of the fpaces meafured by water* It feems that the grains of fine fand are held afunder by the lime pafte, to a greater diflanee than they are by water ; and that the reafon, why the finer fand requires more lime than the coarfer and mixed fand, is^ that the fpaces, which are more numerous in fine fand than in the coarfe, are more augmented in the whole quantity of them, by the particles of lime, which intercede alike the coarfe and the fine grains. SECTION t 97 ] SECTION XIIL Experiments fiewing the Effe^s of fineji Sand and quartofe Powder, in Mortar : Obferva- iions on the finejl calcareous cements : Practical Precepts, r~j~^HE lafl mentioned notion led me to X fufped, foon after the foregoing ex- periments were made, that, although the fine Thames fand made better mortar than the coarfe fand or the rubble afforded, the mortar will not always be the better as the fand is finer, however (harp it be. 1 there- fore procured a large quantity of the very fine pit-fand ufed in London under the name of houfe-fand : I wafhed away the clay with which it abounds, and dried it : viewing it, when thus cleanfed, with a lens, I eftimated the fize of the grains to be, at the medium of the largefi: and fmalleft, about one ninth part of that of my fine Thames fand : this 1 call finefi; fand. At the fame time I was favoured, by my neighbour Mr. Bentley the ingenious manufacturer t)£ the ornamental StafFordfhire ware, with the H neceflary [ 98 ] neceffhry quantity of the fine powder of cal- cined flints, which is prepared for his manu- fadlory. With divers mixtures of thefe with lime water and lime, in a variety of proportions ; and with each and both of thefe, blended with coarfe and fine fand, lime and lime water in fimilar proportions ; I made a great num- ber of fpecimens of mortar, which I tried in the manner already defcribed ; and noting my obfervations on them, I found the following to be the mofl: eligible for the concife recital intended in this eflay. Mortar containing the quantity of lime neceflliry to the plaflicity and other defire- able properties of it, or a greatet quantity of lime, is the more liable to crack in drying, as the fand of it is finer. Mortar made with this fineft fand and lime, does not grow fo hard, or refift fra6lure fo forcibly, as that made with my fine Thames fand and lime, in the fame proportions, or any others nearell: to thefe. But the for- mer mortar, when compofed of about fix parts [ 99 ] pafts of fand, one of lime, and the necef- fary quantity of lime water, and flowly dried, becomes much harder than any of the com- mon calcareous ftuccos, ufed by plaifterers* Mortar compofed of lime, my fine. Thames fand, and the finefh fand, is the worfe as the quantity of fineft fand is greater : ,and this holds true in every tried proportion of the fands and lime. Mortar confifting of lime, coarfe Thames fand, fine Thames fand, and fineft fand, is the worfe as the quantity of this lafl is the greater, when the comparifon is made be- tween it and the cement made with the fame quantities of lime and the beft mix- ture of coarfe and fine Thames fand* Mortar made with flint-powder, lime and lime water, in any proportion, is more liable to crack in drying, than mortar com- pofed of any fand and lime: it is moreovej^ incapable of hardening to fo great a, degree; whether the hardnefs be tried with a chizej, or by breaking it acrofs. But mortar made with about five parts of flint-powder, one o( H 2 lime> [ ] lime, and the neceffary quantity of lime wa- ter, is neverthelefs preferable to any ftucco now ufed in infide work, for the finifhing coat ; becaufe it has a more lively whitenefs, and affumes a finer furface, which I think might be made to imitate that of marble : It requires however to be dried very flowly. Mortar made with coarfe Thames fand, fine Thames fand, flint-powder and lime; or with fine Thames fand, fineft fand, flint* powder and lime; or with the fineft fand, flint-powder and lime ; is the worfe, as the quantity of flint-powder is greater, relative- ly to that of the fand. Upon the whole it appeared, that the fineft fand is injurious in mortar which is expofed to the weather, and that flint-powder is ftill ■worfe: but that this laft may be advanta- geoufly ufeCi in compofing ftucco for infide w^ork, in which, a fine texture, pleafing co- Jour, and fmooth furface, are preferred be- fore extreme hardnefs ; and in which the dry- ing may be regulated fo as to prevent the in- cruftation from cracking. Instead [ 101 ] Instead of refting fatisfied with the bare difcovery of the fa6:, that very fine faiid, or quartofe powder, is incapable of making fo good a cement as may be formed with coarfer fand, although fine Thames fand and lime make a better cement than can be compofed with the coarfe fand and lime; and that the mixture of very fine fand, or filiceous powder, with the Thames fand, is rather in- jurious than ufeful, although the mixture of the fine with the coarfe Thames fand, is better for mortar, than either of them un- mixed ; I took a great deal of pains to learn the caufe of this, in order to confirm or correct the foregoing notions, and render the precepts which flow from this fa6lj the more fatisfaftory* By forting my fineft fand into divers par- cels, in fifting it through different fieves ; by meafuring the mefties of thefe ; and by viewing the grains of each parcel ranked clofely on a fcale ; I perceived, more clearly than I had done before, the roundnefs of this fand: I moreover found that the graiug of the coarfeft parcel were, at a medium of their refpective bulks, upwards of fixteea H 3 times [ 102 ] times larger than thofe of the fineft parcel, the grains of the other parcels being of divers intermediate fizes. As this fand therefore has every advantage attainable by the mix- ture of coarfe and fine grains, and every dif-- advantage refulting from the fmallnefs and foundnefs of its grains, I learned the reafou why the defeats attending fuch fine round fand in mortar, are not corredled by any mixture of coarfe fand. How thefe defeats are induced by the finefl fand and flint-powder, we rnay conceive in the following manner. Having already fhewn how the roundnefg of fand tends to render the mortar made with it defective, I may, without any further illu- ftration of this matter, reckon on this fi-^ gure of the grains of fineft fand, as one caufe of the imperfeclion of the mortar in which it U ufed. There is nothing to prevent the laminae of lime pafle, which intercede the grains of fineft fand, from being as thick, in the mafs of mortar made with it, as they are in mortar made with coarfer fand ; but they are likely to be thicker in general, as the faces of the f^ner [ 1 finer grains are rounder : The number and ex- tent, moreover, of thefe laminae, muft be greater, in the fum, in the fineft fand than in the coarfer : and it is for thefe reafons, that more lime pafte is required to make mor- tar with the former than with the latter; fince the mortar is not formed, until the pafte envelopes every grain, and fills the interftices. In this view of the fubjea, we difcover ano- ther caufe of the defeft lately mentioned. If we ufe lime with a fparing hand, it will not extend between all the grains or fill the fpaces ; we find the mortar too fhort whilft frefh ; and it is as defedive in ftrength, when indurated, as it is deficient of the cementing matter. When we ufe the neceffary quan- tity of lime, the calcareous matter bears a greater proportion to the quartofe grains, in this finefl: mortar, than in the coarfer; and this renders the former defedive, according to the principles of aggregation already exprefled. A THIRD caufe of the imperfe6lion of mortar, made with finefl fand, or containing a large quantity of it, appears, on the confide- ration of the quantity of lime. We have re- peatedly feen that mortar contracts the more H 4 iii^ [ 104 ] In drying, and is the more apt to crack, as it contains a greater quantity of limepafte: and as the finefl fand requires an extraordi- nary quantity of the pafte to form it into mortar, the aggregation of fuch a cement is likely to be impaired by fiffiires, although they do not always appear, by reafon of their fmallnefs. Other caufes, of the experienced imper- fedionof fine mortar, might be added, which have no relation to the figure of the grains of fand or the quantity of calcareous matter ; but to avoid an excefs of theory, I forbear to mention them, and fhall only add a conjec- ture concerning the finer cements. When a cementlous mafs, like mortar, is cut with an edged inftrument, or bro- ken acrofs, we may obferve that the frafture happens in the fhorteft line, along the laminae of the weaker cementing matter, and feldom or never in the fhorter right line paffing thro' the harder grains and the cement alternately, although the imprefled force tend to caufe the folution of continuity in the fhorteft, or in a right line. By the principles of mechanics, the [ 105 ] the refinance to fuch forces is greater, c^^ teris paribus, as the Ihie of fra6lure is longer, whether it he ftraight, or winding in any courfe : and it it for this reafon, that a wall bnilt with very large fquare ftones, is lefs li- able to crack, although the foundation fhould fail near one extremity of it, than a brick wall built with the fame kind of cement on the like ground ; or that a wall, whofe bricks are jointed in the prefect fafhion, is more fe- cure from cracking, than that which fliould be built, on the like infirm ground, with the fame kind of mortar and bricks ftanding over each other, not jointed, but with their fides and ends flufhed, as the workmen exprefs it. As cements are cut and broken In the direction of the cement, and not in the fhorter line; as the cracks in ill-founded walls run wind- ing along the joints, inftead of going in the ihorteft Qourfe through the bricks and joints alternately; and as the refifi:ance of fuch ce- mentlous mafles, eftimated by mechanical theory, is greater, as the line of frafture is neceflfarlly elongated by the flronger aggrega- tion of certain parts of them ; I am inclined to think that calcareous cements made with lime [ !> io6 ] lime and quartofe matter, will always be found weaker, under the trial by the chizel or by fracture, as the quartofe fand or powder is finer ; becaufe the line of fracture, which takes the courfe of the cementing matter, is Ihorter, in any equal depth of fuch maffes, as the hard quartofe grains are finer and rounder. As flint-powder confifls of exceedingly fine grains of filicious ftone worn to roundnefs in the grinding, what has been faid of the finefl fand is fufficient to fhew, why the cements, which contain flint-powder, are the worfl of all thofe we have mentioned. The cuftomary method of wafhlng fand, even for ftucco which is to be expofed to the weather, confifts in paffing it through a iieve, by a circular horizontal motion of it, in a tub filled with water, which flows over, and carries av/ay with it any light mat- ter which can be long fufpended in water, as fail as the fand runs through the fieve into the velTel. But this procefs is inadequate to our views ; becaufe the fineft fand fubfides along with the beil:, and thefe, in the pre- cipitation t 107 ] cipitation, entangle and carry down with them a great deal of finer powder or dirt. Where fuch a method muft be purfued, for want of other iitenfils, or through the fcarci- ty of water, the fand ought to be agitated again in fmall parcels, with a part of the water which has cleared by fublidence ; and immediately after the agitation, the muddy water ought to be poured off, before the light parts have time to fubfide in it. But the ufeful part of the fand is more effedually freed from the finer and noxious parts, by fifting it in llreaming water, whofe current is to be fo managed, that it fhall carry away the mud and the fand which is too fine, whilft the better part fubfides in a proper receptacle. This art may be gathered from the practice of the Cornilh miners, in wafli- ing their pounded ores, better than from any written precepts. In the fubfequent pages I propofe to fhew the integrant parts of gravel, and their feve- ral properties in mortar: for my prefentpur- pofe it will be fufficient to obferve, that the gravel commonly employed in building con- fifts chiefly, after it is (kreened, of rubble^ coarfe [ io8 ] coarfe fand, fine ran4, and finefl: fand, fimi- lar to thofe ufed in o\ir experiments. This is obvious on the bar6 infpe6lion of it, and leads us to difcover afiother caufe of the weaknefs of our modern cements, in the compoiition of which, no other precaution is ■ufed, refpe£ling the gravel, except to fepa- rate the ftones and coarfeft rubble from it, by Ikreening. WriEN it happens that the fkreened gravel contains more than a certain quantity of rub- ble, relatively to that of coarfe and fine fand iimilar to thofe defcribed, the mortar made with it muft, according to our experi- ments, be defective. It will be fo likewife, whenever the coarfe fand of it predominates over the fine fand, to a greater degree than that which was found confident with the perfedion of mortar : and when the quan- tity of finefl; fand happens to be confiderable in gravel, the mortar made with it muft be faulty in a greater degree. Now fuppofijig the gravel to be freed, by the flcreening, from every thing more injurious than fineft fand and quartofe powder, we perceive that the artifl, who is ignorant of the advantages of fizing f 109 ] fizlnghls gravel, and ufes it in its native flate, as chance prefents it, has the odds greatly againft his making good mortar, although he may fometimes do it, without knowing the reafon, as we fhall find hereafter : for his chance is, that the native gravel (hall confift of coarfe and fine fand mixed in the propor- tion of 4 to 3, or of the ruhble, coarfe and fine fand mixed in the proportions above recom. mended; and that it (hall contain Httle or no fand like our fineft fand : but the chances againft him are as numerous as there are other diftant proportions of rubble coarfe and fine fand in gravel, and as the kinds of gra- vel ufed are, which contain the fineft fand or ftill finer quartofe grains, in efficient quan- tity. In great cities, where gravel cannot be procured fo cheap as the rubbifti of old walls, which the workmen lay in the ftreets to be ground to powder by the pafiing carriages, they ufe this rubbifh Ikreened, in the place of fand or gravel, in making mortar. It con- fifts of the grofs powder of bricks, and of mor- tar indurated, as much as bad mortar can be, by time ; and fome builders affirm that it is better [ "o ] better than fand of gravel, for mortar. It is certainly eligible when the price is chiefly confidered ; in any other view, It is not fo. From my paft experience I judged the cal- careous powder of an old cement, and that of the bricks, to be a brittle perifhable and weak fubftitute for grains of fand ; and the quan- tity of dufl: in fuch ground rubbifh, to be highly injurious : but as the opinion of the workmen was againfl: me, I made fome trials of it. I FOUND that lefs lime was requried to make fat mortar with this ground rubbifli, than with my beft mixtures of fand ; which is no fmall recommendation of it in certain jobbs, and is owing, in my opinion,, to the ground calcareous pait, which, fo far as it is finely powdered, is equivalent to whiting : but the mortar made with the rubbifh appeared, in every ftage of induration, and in every com- parifon except that of the plafticity, to be greatly inferior to that made with mixed fand and lime, in the fame proportions. If the workmen would confine their opi- nion to the comparifon of fuch rubbi(h-mor- tar ■[ J tar, with that in which clayey gravel is ufed, or with the cements made with the aflies and ordure of the town, dug out in prepa- ring foundations of houfes, in thofe places which were formerly receptacles of fuch matter, they might maintain it on divers grounds which will be examined hereafter ; but otherwife it is erroneous. SECTION [ "2 ] SECTION XIV. ^xperime?its made on a larger Scale with our hejl Mixture of Sands Lime PP'ater and Lime* 1'N the fpriiig and lummer of the year 1778, I repeated a great number of the foregoing experiments, particularly thofe which exhibit mortar in the improved ftate to which I had brought it ; and finding my former obfervations to be true, when the cir- CLimflances were not varied, I refolved to try my beft cements in larger quantity and in other circumftances. I applied them in the w^ay offtucco, on the brick walls of houfes, in different afpecls, but chiefly in that of the meridian fun ; covering a fquare yard at leaft with each fpecimen, after I had repeatedly wetted the wall with lime water. By thefe trials I found that mortar, made with four parts of coarfe fand and three of fi^ne wetted with, lime water and beaten up with one of my lime flaked with lime water, al- ^ • though. [ ^^3 1 thongh it could be eafily fpread oil a hori- 'Zontal plane, or ufed m biiikling with bricks, was rather too fhort for plaiftering on the per- pendicular furfaee of a wall. It might how- ever be laid on, in fmall fucceffive portions, by a dexterous management of the trowel, and efpecially by Aiding the inftrument on it upwards. When the weather continued temperate and dry for eight or ten days after the in- cruftation was made, and no great quantity of rain fell for three or four weeks after- wards, this ftucco anfwered my expectations; for it did not crack in the leafl:, and in three months was almoft as hard as Portland ftone, at the furfaee, where the induration firfl: takes place for the reafons formerly mentioned ; but it was too coarfe to reprefent a fine grained ftone. Having made two pieces of incruftation of this kind, on the fame wall, and knowing that calcareous cements cannot harden fo foon as it is neceffary in outfide ftuccoing, un- iefs they be pervious to acidulous gas, in which cafe they may drink in water likewiie, I I fre- t "4 ] frequently wetted one of the pieces, in about three months after it was formed., with lime water, expe(fl:ing that the calcareous matter of it would cryfliallize in the cement and render it clofer and harder. I was not difappointed ; for in the courfe of a month I found this piece of ftucco harder and clofer than the former, and at the furface, as much fuperior in thefe particulars, to Portland ftonc, as the other was inferior to it. I have fince found that lime water has not this effect, if the incruftation be wetted with it, before it is quite dry and indurated flowly, to vie with Port- land ftone in that kind of ftrength which is tried by grinding Portland flone on it, or fcra- ping it with a chizel ; for any other trial of in- cruftations is unfair, until the induration lias proceeded equally through the whole mafs. When the incruftations made of the fame cement, were wetted by rain, in two or three days, or fooner after they were applied, and efpecially when the wind blew the rain for- cibly upon them, they were fenfibly injured, for they never afterwards looked or hardened fo well as the former fpecimens of flucco. Ik [ "5 i In tbefe particulars the large incriiflations agreed with thofe made on tiles. But the fame agreement did not appear in the incruf- tations which I had made with the fame compofition, on a wall which fronted the meridian fun, at a time when the weather was very hot ; for thefe fliewed a few (len- der cracks in the courfe of three days. When in the fame fituation and weather, and on a coarfe ftucco of this kind, I fpread, in about two hours after it was laid on, a thinner coat of cement made with finer fand, in order to reprefent a finer grained ftone, the incruftation confining of thefe two layers, cracked more than the former. After many repetitions of thefe experiments, in the hotteft weather, with the fame event, I perceived that the trials of fuch cement on tiles, are not fo fevere as thofe to which they may be expofed fometimes in incruftations on walls. In this latter cafe, the flucco is very unequal in thicknefs ; for in the hollow joints and depreflions of the bricks, it is near an inch thick, when over the prominences it has not more than one-eighth of this thick> nefs ; and as it dries foonefl in the thin parts, 1 2 the [ "6 ] the unequal contraction feems to be the caufe of thofe cracks, which would not happen to the fame cement laid on the flat furface of a tile : it feems moreover that fuch a compoh- tion may more eafily contract in drying, witii- ■out cracking, as the crufl: is made narrower or lefsexteniive. But I impute the cracking chiefly to the foregoing unequal contradlion accelerated not only by the heat of the fun and the wall, but by the thirfty bricks ; for if we form our judgment according to the quicker or flower progrefs of the exflccation, and the fliiffnefs wdiich the cement acquires in the acl of ipread- ing it on the brick wall, the whetting of this lafl: fuperficially with lime water, is not equi- valent to fteeping the tiles for a few mi- nutes in the fame liquor. When, with the view of preventing flf- fures, I ftuccoed a part of the fame wall wet- ted with lime-water with cement containing the mixed fands and lime in the pro- portion of fifteen to two, in the fame kind of Weather, I found the difficulty and walle, in applying it, greater than in the former in- fiances, and that it was defective in ftrength and clofenefs, for want of lime, althongn it did [ ] aid not crack. When, through d'lllruft of my former experiments, I ufed more than one-feventh of hme, the cracks were ftill lar- o-er and more numerous. To guard a recent hicruftation from the rain, and to fecure it from cracking in the circumllances laft defcribed, I propofed the expedient of hanging fail cloth on the cor- nices and fcaffolding : but the expence of this meafure, and the danger of it in windy wea- ther, w^ere ftrong objections. Embarrassed by thisunexpedcd difficulty, Ju-efolved to change my ground, and try what might be done by a new^ feries of expe- riments, in which I intended to ufe every known cheap fubftance, whether itVould be reafonably fuppofed to have any confiderable effea towards fecuring a recent incruftatiou againft the above-mentioned impreliions of rain or hot weather, or could be fufpefted of rendering the ftucco defedive. 1 profe- cuted this enquiry with great alacrity, be- caufe I w^as certain that, although I Ihould fail in the attempt tow^ards improvement, 1 fhould learn how in future to avoid thofe I 3 thiiigs [ ] things, which being natively blended in cer. tain kinds of lime ftone fand or water, tend tq render the mortar made with them faulty. I had already conceived a notion, which I ihali fubmit to my reader before I conclude, concerning the excellence of fome antlent cements ; but left I fliould be mifled by it, I proceeded, in all the experiments which 1 am to relate, on the fuppofition that this ex- cellence is owing to fome matter, accident- ally introduced in the materials, which the Antients found in the diilridls contiguous to their moft durable cementious works, of defignedly blended with their mortar. SECTION [ "9 ] SECTION XV. JLxperiments fiewmg the Integrant Parts of Gra- vel^ the Choice and Preparation of it ; atid the JLffecls of Clay, Fuller s Earth, and terras ^ in Mortar, ON infpecling different kinds of grayel ufed in London and in divers parts of England, in making mortar, I obferved that they all contained fome clay ; and that this was generally coloured with martial matter. In conlideration of the frequency of this mat- ter in mortar, i made it the firll: fubje6l of my prefent enquiry. By the art already defcribed, I forted tiiree bufhels of Ikreened gravel dug up near Port- land Place in Marybone parifli, into five par- cels ; one equivalent to our rubble, another to coarle fand, another to our fine Thames fand, another to our fineft fand ; and the re- mainder was fet apart as clay or bolar earth. I dried all thefe, and reduced the lumps of clay to an impalpable powder. I 4 Having [ J Having treated divers other fpecimens of gravel in the fame manner, I found that gra- ve], freed from the larger pehhles by Ikreen- ing, may generally be conlidered as a native mixture of rubble, finds, and clay ; and that when the clay is waihed, out, the refiduary parts of the different kinds of gravel, differ in fize, fharpnefs, colour and hardnefs ; thofe being the hardeft which coniifl chiefly of quartofe matter. Judging of gravel accord- ing to the precepts derived from my trials of fand, I rank that dug in Marybone amongf]: the better kinds of gravel, and ufcd no othg|: in' mortar. After a great number of trials of ce- ments made with my beft chalk-lime, lime- water and the gravel, or certain parts of the gravel, and applied on tiles and on a wall, I found that thofe made with the coarfe and fine fand of the gravel, fcparated from the reft of it, and mixed in their native proportions, were the befl; that thofe made with the rubble coarfe Lmd and line fand mixed in their original proportions, but containing no other part of the gravel, were the next in hardnefs and the other defireable qualities ; that r I., ] diat tliofc containing all the parts of the gravel except the clay, in their native propor- tions, differed in nothing, that I could difco- yer, from thefe laft, for the ■ fineft fand of this gravel was not a fiftieth part of the mafs of it ; that thofe containing the rubble fands and clay in the fame proportions, and thofe made with the nnwalhed gravel, ap- peared on a clofe examination to be the worft of all thefe : and thofe containing the na- tive unwafhed o'ravel mixed with twice its proper quantity of the clay of fuch gravel, fliewed mofl: clearly that clay is highly inju- rious, by difpofing the mortar to crack in dry- ing, to foften in wet weather, and to moulder when the quantity of clay is one-eighth of that of the fand ; but in much hiialler quantities, it only' prevents the cement from acquiring the hardnefs peculiar to good mortar, and confequently difpofes it to perifli in a few vears. With my heft mixtures of Thames fands lime water and lime, I blended fine fut to- bacco-pipe clay, in different proportions, and expoling thefe fpecimens, I perceived that the cffe£l of clay is greater as it is purer and fat- ter. [ j ter. The fpecimens in which the quantity of fat clay was one-feventh or one-eighth ot that of the fands, mouldered early in the winter like marie. These appearances were not altogether un- expected : for in experiments formerly made with a view to the improvement of §re-vef- fels, I had obferved that clav adheres but weakly to any hard bodies, however flowly it is dried on them, and that mafies compofed of clay and fand in divers proportions, never acquired any confiderable hardnefs by the mere drying and expofure to air : It was therefore not likely that clay fliould add to the ftrength of mprtar ; but as dried clay *greedily imbibes water and fwells with it, and in drying contracts greatly and cracks, if any thing prevent it from contrading equa- bly ; and as marie ftones, which conlift of clay and calcareous earth, moulder in the wea- ther ; it was to be expe6led that clay would be hurtful. These experiments point out another caufe of the defeats of the common mortar, and fhew that the gravel or pit- fand to be ufed in any [ ] • any valuable building, ought to be freed frorn the clay by wafhing, which will be found a very cheap operation, even in cities, if the water which carries off the clay,, be direded into a place where it may be depurated by fub- fidence, for repeated ufe : they likewife dired us in the exannination and choice of thefe, and fhevv that the viler kinds may be made equi- valent to our beft mixture of Thames fand, or nearly fo, by walhing and forting, and then rejeding the excefs of rubble or £ne fand. I MUST obferve however that fome kinds of gravel cannot be made fit for mortar by this procefs: for the grains of them, which re- femble thofe of rubble and coarfe fand, confift of fmaller grains cemented by clay, which is fo far indurated that it cannot difFufe itfelf in the water fpeedily, Fullers earth tried in the fiime manner was found to operate in the mortar like clay, in every refped, as 1 might have prefumed, except that the former was lefs injurious than the clay, when the quantities of them were equal, Terras, [ ] Terras, which is a volcanic produclioii coniiiling chiefly of clay and calx of iron in- durated together, when it was ground to an impalpable powder, produced the efFe6ls of fuller's earth, in mortar, the more fenfibly as it approached nearer to be one-feventh of the quantity of fand. The coarfer powder of terras had lets effect. A MORTAR made of terras powder and lime was ufed in water fences by the Remans, and has been generally employed in luch ftru6lures ever fnice their time. It is pre- ferred before any other, for this ufe, becaufe it fets quickly, and then is impenetrable to water : whence fome people haftily conclude that it is the heft kind of mortar for any pur- pofe. But by experience I know that mor- tar made of lime and terras powder, whether coarfe or fme, will not grow fo hard as mor- tar made with lime and fand, nor endure the weather fo well ; but on the contrary is apt to crack and perifli quickly in the open air. The efficacy of it in water fences is experi- enced only where it is always kept wet, and feems to depend on the property which the powder of terras has, in common with other [ ] indurated argillacious bodies, and efpecially the boles, but in a higher degree, of expedi- ting the cryftaUization of the calcareous mat- ter, by imbibing the water in which it is diffufed in the mortar, and of fweliing, du- ring this abforption, fo much, as to render the cement impenetrable to any more water : it feems alfo that an acid of the vitrioHc kind, which is contained in terras as well as in boles, contributes to the fpeedy fetting of this cement, by reducing a part of the lime to the condition of gypfum. SECTION [ '^6 ] SECTION xvr. Experimenfs f Jewing the Effe3is of Plaijier Pow^ der^ Alum, Vitriolic Acid, of fome metallic and earthy Salts, and of Alkalies, in Mortar, Pradlical Inferences, IN my befl mixtures of coarfe and fine Thames fand with one-feventh and with larger quantities of Hme, I tried the gypfeous powder of which plaifter of Paris is made ; and found it to be injurious in proportion to the quantity of it. The particular effe^Sls of gypfum in mortar, were fuch as might be ex- pelled in confequence of our knowledge of the faline nature of it ; gypfum being a com- pound of calcareous earth and vitrioHc acid, which is foluble in water, not fo freely as neutral falts, but rather like lime : it difpofed the mortar to fet fafter than it could be ap- plied in ftuccoing ; it contributed very little to the plafticity of it ; and the cement was the more apt to foften in wet weather and to pe- rilh in time, as the quantity of plaifter pow- der [ ] Jer ill it was greater. The greatefl quantity tried was only one-feventh of that of the fand. Alum was found very injurious. The acid of alum formed felenite or gvpfum with a part of the lime, and thus operated like gypfum or plaifter powder ; w^hilft the earth of the alum induced the imperfet^lions which attend the ufe of clay. The greatefl quan- tity of alum ufed was one part in ten of the beft mixture of fand and lime ; and this fpe- cimen mouldered, in nine or ten months, Hke marie. Vitriolic acid, which formed felenite or gypfum with a part of the lime, produced the effedls of a quadruple quantity of plaiuer powder. Vitriols of lead and of tin, being decom- pofed by the lime, operated like fraaller quan- tities of vitriolic acid : martial vitriol or cop- peras had the fame efFeft, and induced an olive colour, which was foon turned to that of rufl. VlTRIQL [ ] Vitriol of zinc or white vitriol, and Epfom fait, did not difpofe the mortar to let haftily, nor injure it in any particular difco- verable during the application and drying of it ; for thefe vitriols are not eafily decom- pofed by lime : but afterwards I perceived that they impeded the induration of the flucco, and difpofed it to fufter by the wea- ther, the more as the quantity of either of them came near to be one-tenth of the quan- tity of fand. Vi THIOL ATED tartar, Glaubers fait, and the falts which are found in moft of our wa- ters-, fuch as fea fait, nitre, marine calcareous fait, calcareous nitre, and that compofed of magnefia and marine acid, were found like Epfom fait to injure the beft mortar : fo were cauftic mineral alkali ; cauftic vegetable al- kali ; and liquor filicum. Cauftic volatile alkali, which foon exhales by reafon of its volatility, had no fenfible efFe^l. I did not try argol or mild alkalies, becaufe they reduce the lime to whiting ; neither did I ufe any acid which forms a very foluble fait with lime, for obvious reafons. Knowing r ] Knowing that the Ume which has been employed by foap- boilers to render their ba- rilla and pot-afh cauftic, contains, even after the repeated elixations, a little alkali and vitriolated tartar blended with the calcareous earth ; and that the greater part of this laft is reftored to the condition of chalky by the acidulous gas imbibed from the alkaline falts ; I had, in confequence of the foregoing ex^. perimentSj fufficient reafon to prefume that this refufe matter of the foap- boilers cannot anfwer the purpofes of lime^ or improve our mortar. But as a pretence to the contrary is made by fome artiftsj and appears in the Builder's Diftionary, and as the cheapnefs of this article is a temptation towards their extending the ufe of it, I refolved to decide this queftion by direct experiment. After trying, in my ufual method, fpe-^ cimens of mortar made with the refufe of foap-lees and my beft fand, in different pro- portions ; and others made with this fand, lime, and the refufe matter, in various pro- portions ; I found the firft deftitute of the rnofi: ufeful properties of good mortar ; and the others were defective, in proportion to the K quantity [ 13'^ ] quantity of the refufe matter relatively 'to that of the lime. Whether this matter im- proves mortar made with gravel and the com- mon chalk-lime, or encreafes the defeds of it, is a queftion not worth our notice. The experiments lately related fhevv that lime is the more unfit for building and ex- ternal incruftations, as it contains more gyp- fum; and I muft now remark that moft kinds of lime-ftone ufed in England con- tain confiderable quantities of this matter which is not much corrected in the burning : But as I have, in the fecond fedion, enabled my readers to difcover this imperfection, I hope I fhall be excufed from the invidious office of depreciating or recommending any particular lime-fl:one or manufadory ofHme. The cautions which our lafl: mentioned experiments fuggeft with regard to the ufe of water, are efpecially neceflary in this country, where moft of the wells and fprings abound with one or more of the above- mentioned falts ; and it is not to be prefumed that the quantity of thefe contained in water which is ufed for culinary purpofes, cannot be [ '3' 1 be injurious in mortar ; for I know that fe- lenite, Epfonx fait, the very dehquefcent falts compound of magnefia and marine acid and of calcareous earth and the fame acid, may^ together with a little fea-falt, be natively dif- folved in water, to the quantity of half an ounce in a gallon, without alfeding the tafte of it feniihly. When we confider the quan-^ tity of water neceffary in flaking the lime making the mortar and wetting the thir- fty bricks, and the fmallnefs of thofe por- tions of falts, whofe injurious effects were difcoverable in the courfe of one year, or in a fliorter time, we find fufficient grounds for concluding that fuch faline waters will be found hurtful in mortar, before many years elapfe, particularly w4iere it is expofed to moifture. Indeed this has been already ex- perienced of fea-falt, even in the fmall quan- tity of it introduced in mortar, when the fand is taken from the fea fhore. The eafieft method of difcovering the quantity of faline matter in water, confifts in evaporat- ing it flowly to drynefs and weighing the refidue : water which depofites calcareous earth as foon as it is heated, ought to be cleared by fubiidence or filtering, before the evapo- ration is compleated. K 2 yVHEVt [ ] When a choice can be made, rain water Is to be preferred ; river water holds the next place, land water the next, fpring water the laft ; and waters noted medicinally or other- wife for their faline contents, ought not to be ufed at all in mortar ; for the falts con- tained in them are thofe which were tried? the vitriolated tartar excepted. ^ SECTION [ 133 J SECTION XVII. Experiments Jhewlng the Effedls of jk'immed Milky Serum of Ox-Blood, 'Decodiion of Lint feed. Mucilage of Lint feed, Olive Oil, LintfeedOilj mdRefin, in Mortar ; and the Effe^ of paint^ ing calcareous Incrufiations, AT the fame time and in the fame mix- tures of the befl fand and lime, I tried fkimmed milk, ferum of ox-blood, decodion of lintfeed flrained, and thick mucilage of lintfeed, in the place of lime water. The mortar made with any of thefe was fatter as the liquor was more glutinous, but was as liable to crack as mortar made with, water. In the courfe of a year it appeared that each of thele liquors encourages a vege- tation to take place on the furface, which gives it an ugly appearance, and tends to ruin it ; and that they all prevent the cement froiu acquiring the experienced hardnefs of K 5 our [ '34 ]■ ©iir beft compofitions, or indeed from having any competition with them in this particu- lar. The notion therefore which is entertained by the builders, concerning the ufe of Ikini^ xned milk and blood, is erroneous, unlefs it ■je confined to the viler kinds of mortar, iiich may perhaps be improved by them ; b ciufe a compofition of find whiting and mucilage, grows harder than that of whiting and fand kneaded with water. It feems to me that glutinous liquors and good hme a6l reciprocally on each other, in the time of mixing them, to the deflru£liou of their refpedive charaders, and particular- ly to the converfion of a part of the quick Jime into whiting ; and that if any kind of mortar is improved by them, it is then efpe- cially, when the workman takes advantage of the fatnefs induced by them, and ufnig lefs than his cuftomary quantity of lime, fecuresi his work from cracking, Olive oil mixed with good mortar, or fub- ftituted in the place of a part of the hme wa- ter. [ "35 I ter, rendered the cement defedive, as the quantity of oil was greater. The greateft quantity ufed was half that of the lime. Lint SEED oil ufed in the fame manner, makes the mortar fatter, retards the drying of it, and prevents it from acquiring in any time, io great a degree of hardnefs as it other- wife would have. It was the more hurtful as the quantity of it was nearer to that of half the lime : in much fmaller quantities it was lefs injurious than olive oil. From my obfervations on this fubje^t, and on the com- pofitions called oil cements, I have reafon to conclude, that no oil ought to be ufed in a cement which conlifts chiefly of fand lime and water ; nor any water or watery liquor, in a cementious mixture, which is moiflened and kneaded with oil chiefly. As lintfeed oil whiting and fand make a ce^ ment which hardens to a great degree, in dry fltuatipns, and abides the weather a longtime before the hardened oil relents, it is not im- probable that lintfeed oil may meliorate mor- tar made with bad lime. But good lime and lintfeed oil feem to injure each other, in form^ K 4 ing [, '36 ] ing a kind of faponaceous compound with the iinie water of the mortar. From the experienced effe£ls of faline, ge^ latinous, and oleaginous matter, 1 infer that cow-dung, which I have not tried, would im- pair good mortar. It makes the common mortar fatter, and in that refpecl more con- venient for pargeting the interior furfacc of chimney flues : it feems likewife to prevent the parget made with bad lime, from drying fo quickly and from cracking fo much as it otherwife would do ; the fibrous part of the dung being capable of contributing largely to this latter effed. On thefe grounds it may be ufeful in bad mortar thus applied, whether it increafes the hardnefs of it or not ; altho^ it is likely to impair good mortar, Powder of refin intimately blended with mortar by grinding it with a part of the lime and lime water, was hurtful according to the quantity of it ; the greateft quantity tried be-* ing one-fourth of that of the lime, Before I knew the event of thefe experi- inents I made an inciuftation on a wall front- ing I '37 ] ingthe fouth, but lhaded from the fun after mid-day, with a cement compofed of feven parts of my mixed fand, one of the beft ftone lime, and the neceflary quantity of lime wa- ter. As foon as the incruftation was dry, which happened in four days, I painted one- third of it with lintfeed oil prepared for pain- ters ufe, another third witii white lead paint, and the remainder was feparated from thefe by a channel cut between them. After fourteen months the laft-mentioned portion was very hard near the furface, and the induration extended deeply in the mafs of it, though not in fo great a degree of perfec- tion as that of the furface : The painted por- tions were alfo very hard at the furface, but internally much weaker than the other. From my obfervations of thefe fpecimens, and of divers incruftations in this city, which being made of bad calcareous cement,have been painted and fanded, in order to fill the cracks and fence them from the weather ; I have had fufficientrealon to conclude, that an incru- ftation, made as good as it may be with lime and fand and lime water, i§ not bettered by paint- ing [ '38 ] Hig it as fooii as k dries; that this covering retards the induration of it, by cutting off its communication witli the air ; that it there- fore renders it liable to be irreparably in- jured in wet weather, wherever the water can get behind the paint ; and that if paint or oil ought ever to be applied on fuch itucco, it ought not to be ufed in lefs than a year after the incruftation is made : I like- wife found that the painting and fanding of the common defective incruftations, contri- butes very little to their duration, although jt hardens them at the furface ; for it does not effe^ually prevent them from cracking ; ^nd it avails very little to paint the cracke.d flucco again ; becaufe cracked ftucco is al- ways hollow, as the workmen term it ; that is, it parts from the wall in the parts conti- guous to the cracks, founds hollow on being ftruck with the knuckle, and falls off in a few years, if it be fo thick and large in ex- tent as to break the adhering portions by its weight. SECTION [ '39 3 SECTION XVIIL Experiments Jloewlng the EfeSl of Sulphur, m-r troduced by different Methods, in Mortar, IN my firft trials of fulphur, it feemed to be ufeful ; and this led me to try it in fo many different ways, and in fo many mix- tures of lime and fands, and of thefe with flint powder and divers other fubftances, as would render the recital of all my obferva- tions on the effe6^:s of it inconftftent with the plan of this effay : I muft therefore content myfelf with communicating thofe which I think moll: ufeful, in fuch terms as may give Ibme intimation of the manner in which the experiments were made. When the livlgated powder of fulphur was mixed with mortar already made of good ma- terials and did not exceed one-thirty-fecond part of the mafs, it feemed to improve it, in the firfl and fecond month, and fometimes during a longer time of comparifon with mortar [ UO ] mortar made of all the fame materials, ex- cept fulphur, ill fimilar proportions : But in ten or twelve months the fulphur was found injurious, and the more fo, as it exceeded the foregoing proportion. The mofl hurtful ef- fect of it was, its difpoiing the mortar to re- lent in long continued rains, and grow quite friable after a few alternations of freezing and thawing. It had the fame eHedl in mortar containing feveral of the ingredients already named and of thofe hereafter to be mentioned. When the fulphur was mixed with frefh powdered lime, and thefe were ground brilk- ly with lime water, a calcareous liver of ful- phur was formed, proportionate to the quan- tity of fulphur ufed ; and the mortar made with this mixture and land, or with this and fand and other ingredients, was worfe than mortar containing an equal quantity of the fulphur mixed in it in the former method. The tranfparent liquor called liquid cal- careous liver of fulphur, which confills of fulphur diilblved in water by the inter- vention of lim.e, being ufed inftead of water in making mortar with fand and lime in any proportions, was found more in- jurious [ HI ] jurious than three times this quantity of urr- diffolved fulphur was, in the firfl-mentioned method of ufing it : and this liquor had the like efFed in mixtures of mortar with divers other ingredients. Whence I infer that ful- phureous mineral waters ought not to be ufed in mortar. If the plan of thefe experiments had not comprehended the noxious as well as the ufe- ful ingredients, and I had not refolved to dlftruft every theory, I might have prog- nofticated the event of thefe mixtures, in confequence of my certain knowledge of the Operation of fulphur lime and air on each other. When fulphur and lime are moiftened with water, and expofed to air, the acid of fulphur being attraded by the lime, whilft the phloglfton of the fulphur is attraded by the air, a decompofition of the fulphur takes place, and new compounds are formed. The acid and lime gradually form felenlte orgyp- fum, whilft the air combined with the phlo- glfton is wafted away. Therefore lime, by fo much of it as is thus expended in forming gypfum^ [ ] gypfum, is not only unable to ^S: as a du- rable cement of the grains of fand, but is capable, according to the experiments of the Cxteenth fedlion, of counterafting the ce- menting powers of the refiduary part of it, when the mafs of fulphurated cement is ex- pofed to the weather. The pleafing warm colour which fulphur induces in calcareous ftucco, whilft it is frefh, and the promiting appearances of fuch an incruftation in the lirfl; year, have, if I am rightly informed, already mifled an artift to apply it freely at his own rifque. I wifli thefe obfervations may ferve to undeceive him. About this time, the imitation of coloured ftones, by incruflations, became an objed of my attention ; and fome of the fubfequent experiments were made with a view to it, as well as to the purpofes already expreffed. SECTION [ H3 ] SECTION XIX. Exper iments fiewing the Effedis of Crude Anil' mony, Regulus of Antimony, Lead Matt^ Potter's Ore, White Lead, Arfenic, Orpi- ment. Martial Pyrites and flaked Mundic^ in Mortar. CRUDE antimony reduced to an impal- pable powder and then ground with the lime and lime water, operated in mortar as fulphur does when it is ufed in the fame manner and in the quantity which the crude antimony contains. The antimonial powder moreover induced a difagreeable blueifh co- lour, which in a little time became browa and afterwards yellowifli. When the powder of antimony was mixed in the mortar after it was made it was lefs injurious. Regulus of antimony tried in the fame way, feemed to have no other effed than that [ 144 ] that which is produced by the admixture of fiint powder or other fine powders of hard bodies. Powdered lead matt and potter*s ore of lead aded like crude antimony^ but more flowly and weakly in equal quantities of them. White lead was found exceedingly inju- rious, which I expeaed ; for I had long be< fore difcovered and fliewn in my pubhc Courfes of Chymiftry, that a great part of white lead is acidulous gas, into which vine- gar is eafily convertible in the procefs for making white lead and in many others ; and 1 forefaw that the hme, attraftlng this mat- ter, would be reduced to the condition of whiting in the time of making the mixture^ and that the mortar would confequently be defedive. The white lead, as faft as its aci- dulous gas is drawn from it by the lime, be- comes yellow like mafficot. As white lead improves the oil cements, thefe experiments, fhew that there is no true analogy between the calcareous water cements and thofc which are called oil cements. Arsenic [ 145 J Arsenic operated in mortar like the neutral falts ; and orplment produced the injurious effects experienced of fulphur and of arfenic y which efFe£ls were greatefl: when the orpi- ment was ground with the unflaked lime and lime wateri Orpiiiient imparted a dark brown colour at firft, which foon became yellow and afterwards difappeared. The martial pyrites called mundic, heated to rednefs, and then flaked by moiftening it with water whilft it was hot^ operated like crude antimony, with this difference only, that a greater quantity of it was required to produce the fame efFe£l ; for this reafon, as I conceive it, that the quantity of fulphur in martial pyrites is lefs than in crude antimony, and being held in it by a more forcible at- traction, is prevented from acting fo freely on the lime of the rhortar. The colour induced by the flaked mundic was at firft blueifli and afterwards turned to that of iron ruft. The mundic, which was that of Wiel- Virgin in Cornwall, ufed in its native ftate, in mortar, kept me in fufpence upwards of twelve months. It was tried not only ori L tiles^ [ U6 ] tiles, but ill large incruftatlons on walls, be- caufe it promiled great advantages at firil:. When the quantity of it did not exceed one twenty- fourth of that of the mortar, it mani- feftly increafed the induration of the cement during the firft nine months ; but after fourteen or fifteen months it difpofed the incruftation to relent, the more as it was oftener wetted or as the place was damp, and from being exceed- ingly hard, to become penetrable to a pointed inftrument pufhed only with the hand, and as brittle as chalkftone. The colour and changes of colour of the mortar containing native mundic, are fimilar to thofe produced by the flaked mundic, and are not at all plea- fing to the eye. The effects of much fmaller quantities of this matter in mortar do not yet appear fo clearly ; but there is no reafon to prefume that they will be of the fame kind, though in a fmaller degree. These and the preceding experiments in- dicate that all bodies foluble in water, not ex- cepting arfenic, and all thofe which are capa- ble of efflorefcing, or of being decompofed by air and moifture, are hurtful in mortar ; and they teach us to avoid thofe kinds of gravel which t H7 ] which are impregnated with pyritous matter, whether it be arfenical, metallic, aluminous, or calcareous. The effeds of regulus of an- timony, and the fpeedy decay of the cheaper metals, however perfedly they are defulphu- rated, give ftrong grounds for prefuming that calcareous cements, which are to be expofed fully to the weather, are more likely to bo injured than improved by metallic matter in- troduced in any form. Li SfiCtlON [ uS ] SECTION XX. Experiments JJjewing tide EffeSis of h'on Scales, wajhed Colcoihar^ native Red Ochres, Tellow Ochres, Umber, Powder of coloured Fluor, coloured Mica, Smalt, ajid other coloured Bo- dies, in Mortar. Advices concerning coloured Incrufiations, Infide-Stucco , and damp Walls, IRON fcales from a fmith's forge, which confifl of iron femi-calciiied, and are thought by many artifts to improve mortar, were tried eighteen months ago, by grinding them to a fine powder, and mixing this in mortar, to half the quantity of the lime, and in fmaller proportions. The larger quantities, in the courfe of twelve or fourteen months, appeared to be hurtful ; and by thefe I judge of the fmallefl:, which do not yet appear to produce any re- markable efFed in incrufiations made in dry fituations, except the rufty colour which they induce. But in thofe which reached • near [ H9 ] near the ground, and in others made on tiles, which were laid flat on the ground in a fha- ded damp corner, in both of which inftances the incruftations were always moift, the iron powder feemed to render the cement a little -harder than it could otherwife become in the fame time in fuch circumftances, and it certainly made it clofer in the grain. By thefe experiments I am inclined to think that iron powder, which, during its con- verfion to ruft, imbibes a great deal of aci- 'dulous gas and air, and fwells confiderably, may be ufed with fuccefs, where the proper induration of good mortar is prevented by continual moifture, and the chief purpofe of the cement is, to exclude water perfedly, by the clofenefs of its texture, to which the fwelling of the iron contributes not a little. If it is capable of producing any defireablc eiFeds in cements otherwife circumftanced, thefe are to be expeded only when the quan- tity of it does not exceed one-eighth of that of the lime, or one-fiftieth of that of the mafs of mortar. Washed- [ MO ] Washed colcothar of iron, native red ochres, yellow ochres, and umber, had the efFefts of fmaller quantities of terras, or of equal quantities of flint- powder. Coloured fluor and micaceous ftones, co- loured marble, fmalt, and divers other co- loured fubflances, which are infoluble in wa- ter, reduced to fine powder, induced their re- fpeclive tints in the incruflations, but acled like flint powder. From the experienced effeds of coloured calces of iron, and of divers fulphurated and perifliable metallic powders, I learned that thefe ought not to be ufed in external incruf* tations ; fince they render them more defec- tive as they colour them deeply ; and 1 turned my thoughts to the difcovery of fome other expedient for inducing permanent colour without injuring the cement, I SOON found that this may be done, with regard to the lighter and pleafanter tints, by the ufe of coloured fands, or the cqarfe gritty forted powder of hard and durable coloured bodies, Lynu (md afFord?i a white cement which [ "i- ] which is the better, as mare of the finefl part is lifted out of the fand. Thames fand makes a grey cement not unHke Portland ftone, and this colour is agreeably varied by the ufe of grey bone-afh, of which we ihall prefently treat. A RICH yellow tint is obtained by ufing the golden yellow fands, of which kind there is one near Croydon in Surrey ; and a fmall quantity of this fand mixed with Lynn fand, gives a warm white, and with Tliames fand, an exa6t refemblance of the Bath ftone. Thefe are the moft eligible tints for the fronts of houfes. Until I had tried the gliflrening fcaly talcs, I imagined they would ferve to impart all other tints, as they may be had of any colour, and are as durable as they are plea- ling to the eye : but they were found to weaken the adhelion of the cement to the wall, and to make it fo rough and (hort, that it was almoft impoffible to form a fmooth compact incruftation with it, unlefs the lime were ufed in exceflive quantity ; and in the CQurfe of eight or nine months it ap- L 4 peared [ ] Reared that the cements, in which they were mixed in the quantity necelTary to produce ftrong tints, were rendered Ipongy, and greatly weakened by them, ' Scaly gliftening mica, ftrewed equably on an incrnflation previoufly wetted wath a thin mixture of lime water and lime, and gently comprefled to lay the fcales flat, im- parts its colour with the fulleft effed. In this way coloured mica may be ufed, where it is cheap, on external incruftations, if the ■perfpedive appearance of a building can be improved by different colours of any members of it: and this kind of colouring greatly ex^- eels painting, in the fickle weather of our cli- mate, becaufe it lafls unfaded, as long as the micaceous crufl:, To tinge a cement fufficiently for prof- pe£t or contraft, of any colour w^hich is not found in fand, fo that the incruftation fhall not be impaired, and that the colour ihall be as durable as the cement ; I found nothing more advifeable than to ufe, in the place of the fand, or of a part of it, coloured glafles or coloured flones of the hardell: kind/ beaten to . - ^parfe [ '53 ] coarfe powder, the finer parts of which are to be wafhed away, not merely becaufe they 55 1 the mnteiials of them are fo fpongy as to im- bibe the ram, and the circulation of air with" in the houfe is not fufficient to waft away the rnoifture which tranfudes from the wet wall into the ftucco; and efpecially when the ex- halation of this moifture from the ftucco, is impeded by the clofenefs of its texture ; for all fuch bodies retain moifture the more for- cibly, as their pores are fmaller, and as the air meets more difficulty in pervading them. I fee no reafon to doubt that this inconve- nience would be obviated by making the in- cruftation of a texture fimilar to that of the xnaterials on w^hich it is laid ; and that the cement made with about feven parts of fand, one of Hme, and the Hme water, and im- proved, as wc ihall teach hereafter, by the admixture of bone-afh, would continue dry in fuch circumftances, becaufe moifture quickly exhales from it, by reafon of its tex- ture. The damp which feizes Incruftations, when the walls are badly conftru^led, wheu the joints of the facing bricks become holjow by the decay of the mortar, or when the co- pings r ] pmgs or gutters are defe6live, do not fall un- -der our confideration. The damp by condenfation appears moft on the fineft and clofeft incruftations, however perfed and old the walls may be. To find the proximate caufe of it, we need only to advert to that which gathers on glafs windows, whilft the wainfcoat and other fpongy bodies, which ferve to inclofe the fame rooros,remain dry; or to the moiflure which gathers on walls faced with the clofer kinds of ornamental marble, in fumptuous buildings,at the fame time when the walls and incrufhations, which are contiguous to them, and are of a coarfe texture, are quite dry. In thefe and other inftances we may perceive, that the damp is owing to the clofenefs of thefe bo65 ] for the greater part, of charcoal, which af- terwards is beaten finer in making the mor- tar : The afhes ufed by builders whofe dura- ble works authorized this pra6tice, might have been the refufe of manufactories of pot- afh, in which the faline matter is always carefully extradted from them ; and charcoal powder or elixated afhes may greatly improve mortar, akho' afhes finely fifted and replete with falts fliould impair it. I therefore boiled my calcined wood-afhes in water, and repeated this operation twice in frefh water; knowing that one elixation does not free the afhes per- feftly from the faline matter : I then dried the infipid afhes thoroughly, and ufed thenx in this ftate, under the name of elixated wood-afhes. At the fame time I provided charcoal powder fifted thro' the fame fieve which I ufed for the wood-afhes. After a great number of experiments made in the ufual manner with the elixated afhes, I found that they rendered the mor- tar fpongy, difpofed it to dry and harden quickly, and prevented it from cracking, more effedually than the like additional quan- tity of fand would do it. They did not ap- M 3 pear [ i66 ] pear to induce the defeds attending falins bodies in mortar ; they only made it weaker, as the quantity of the elixated afl^es was greater relatively to that of the fand or lime;. This weaknefs, however, was uqt fuch as the unwalhed afl"ies or faline bodies produce, but rather of the kind which I pointed out in thofe parts of the foregoing fe£lions, wherein I endeavoured to fliew, that cemeu: tious mafles refifl: edged inflrunaents or any force tending to break them, the more weak^ ly, as they contain rnore of the fofter and brittler calcareous matter, or as fofter grains are fubflituted for a part of the fand. In every cornparifon of the fpecimens con^ taining unwafhed wood-afhes, with thofe in which the elixated afl^es were mixed in the fame proportions, it clearly appeared that the latter are to be preferred ; and that nei- ther of them ought ever to exceed half thq quantity of lime, in good mortar. As flint powder and other earthy pow- ders were found to difpofe mortar to , crack, I could not conceive how the elixated wood- aflies operated fo efFe and the pthers, a blueifh or fiate colour, ftili more pfFenfive to the eye ; for which reafon they [ '69 ] are unfit for any work that is not hid from the view. As my reader may not fully underftand what I briefly mentioned concerning the (tsnfible difference between thefe h{\- examin- ed powders, and others noticed in the pre- ceding fe<9:ions, I will thus exemplify my notions. Wood confifts of watery and vola- tile parts which are expelled by heat, and of fixed parts which conftitute the charcoal : and charred wood, which greedily imbibes air or water in great quantity, may be con- lidered as an affemblage of capillary tubes of divers figures and iizes. So we may likewife confider the fragments of charcoal, and each vilible grain of its powder. But as the mcft brittle bodies are flexible when they are made fufficiently thin, the charcoal powder is an aflemblage of fmall flexible or compreffible tubulated bodies. As the charcoal which is the more fixed and folid bafis of wood, is fpongy after the juices are expelled in charring ; fo the afhes of charred wood are, after the elixation, an gflemblage of fpongy or tubulated grains out of [ 170 ] of which the phlogiftic matter has efcaped dur- ing the combuftion : and the texture of thefe grains differs from that of the grains of fine land or of flint powder, in the fame manner, if not in the fame degree, as the texture of fponge differs from that of a flint. And we may conceive the unwafhed wood afhes, as a heap of fmall fpongy bodies clogged with al- kaline fait. Upon the fame grounds, the relation of coak or fea-coal-cinders to the raw coal, is analogous to that which charcoal bears tq wood, or fpongy pumice flone to porphyry \ and transferring thefe obfervations to bones, and confidering the fmaller veflels and finer texture of them than of wood, we fliall find the powder of charred bones to confift of tu- bulated or fpongy bodies like thofe of char- cpal powder, \iut pervious by flenderer and harder tubes ; and bone-afh, which is the gritty powder of well burnt bones, to have the fame relation to the charred bones, which elixated wood-alhes have to charcoal powder. Thus I have thought of thefe fubftances, after having obferved wh^t happens to them ii> [ ^7? ] in the preparation ; examined them by a mi- crofcope ; experienced their effe£ls to be fa different from thofe of finefl fand, or pow- dered fldnes, in mortar ; and finally difcover- ed, by repeated experiments, the detail of which is not np\y neceffary, that femivitrir fication, which deflroys the fpongy texture, and levigation, which breaks thefe fpongy grains down to the particles of which they are conftrucfled, render charcoal powder, wood-afhes, powdered fea-coal-cinders, and others of the like kind, incapable of ading in the rnanner dpfcribed, in calcareous ce-^ jnents. All thefe things being confidercd, I inv pute the effects of thefe afhes, or powders, to the tubulated ftrudufe and compreflibiiitv of the integrant parts of them ; and in tho next fedion I fhalj offer all that I have at- tempted further, theoretically or practically, relative to this fubjed. SECTION [ j SECTION XXII. Experlmenis Jbewing the Effects of white and grey Bone- ajhes, and the Powder of Charred Bones ; and 'Theory of the Agency of thefe in the beji calcareous Cements, LONG before I had tried all the powders heretofore mentioned, I ufed bone-afh in many experiments, and faw the efFeds of it in mortar. For the fake of brevity and perfpiculty I referred the relation of thera for this feclion : and in order to fhew more clearly the analogy in texture, between bone-afhes and the powders lately men- tioned, and to fuggeft the means of pro- curing them in any part of this country, I will premife ^ Iketch of the moft pro- fitable proceffes by which they are prepared, at a moderate price not much exceeding that of good ftone-lime. The [ '73 ] The bones colleaed in great cities, are broken to fmall fragments in a mill, and boil- ed in water, in order to extricate and fave the oil of them. They are then put into a large iron ftili, through an aperture which is flop- ped up clofely after the charge is made. Th© ftill, which opens into an apparatus of re- frigeratory vefl'els, is heated gradually to red^ nefs, until all the volatile alkali, commonly called fpirit and fait of hartfhorn, is expelled from them, together with empyreumatic oil, water, and certain elaftic invifjble fluids : The alkali, being the only valuable articW amongft thefe, is retained and condenfed ia the refrigeratory tubes and veffels with all poffible care, whilft the elaflic fluids, left they Ihould burft the veffels, are fuffered ta efcape in places diftant from the fire or the,- flame of candles, becaufe they are combufti- ble, and if they catch fire whilfl air remains in the condenfing veffels, explode like gun- powder. The bones thus heated without being ex- pofed to the air, are charred to blacknefs, but ftill remain combuflible. When they are required in this flate, the iron flill is kept f 174 ] kept clofed until they cool, and then the blackeft of them are ground to fuie powder, which is ufed as a fubflitute for ivory blacky which IS prepared in the fame way , from ivory. The coarfer powder of thefe, is what i undeirftand by powder of charred bones. But when this is not the manufacturer's de- sign, the door of the iron fcill is opened whilft it is hot, and the charred bones, which flame and burn when they meet the air, are thrown into a kind of kiln, at the bottom of which the air can freely enter, and main- tain the combuftion, until the bones are burned to whitenefs, for the greater part. The white fragments are picked, and rather bruifed, than ground, to a gritty powder, by a millftone which rolls on them vertical- ly over an inclined circular plane. This powder pafled thro' a fieve is called bone- afhes, which are much ufed in metallurgy, and fitter for our purpofes in incruftations, than the powder of burned bones ground as pigments are. The fragments which have not been thoroughly burned in the kiln, form a dark grey powder ; and mixtures of the white and grey burned bones afford bone- afhes of the lighter grey colours. The t «75 ] The whole quantity of bone-afhes, which is to be ufed in the fame incruftation, ought to be well mixed ; for it is impoffible to fort the well burned or the grey bones fo accu- rately as to fecure an unity of colour in the parcels of powder which are fucceffively pre- pared, and a very fmall variation of colour will be feen in the incruftation. Mr. John Oliver of Hoxton, who is a ve- ry liberal and ingenious artift, prepares bone- a(hes, judicioufly adapted to the purpofes which I am now to mention, at a very low price, as well as the coarfer kind which is ufed in making cupels and tefts by the refin- ers. I (hall diftinguifh the former by the name of forted bone-afhes ; becaufe they arc freed from the fineft and the coarfcft parts of the latter. As I knew that bone-aflies confift chiefly of calcareous earth, and may be reduced to lime, by diflblving them in acids, precipitat- ing the folution by alkalies, wafliing the pre- cipitate perfectly and then burning it, I tried them with fand in different ways, in order to learn how far they refemble lime in their ce-v menting [ >76 ] ffienting properties ; and found that the fort- cd bone-aflies had very httle efFed ; but that compofitions made with the levigated pow^der of thefe and fand and water, were nearly e- qual in hardnefs to thofe made with whiting and fand kneaded with water in the fame proportions, and were not fo liable to crack* Hence 1 inferred that bone-aflies, of which five-iixths are calcareous earth, could not im- prove mortar by any augmentation of the ce- menting powers of the lime, although they might be ufeful in other refpeds, and that they could not fupply the defect of lime in quantity or quality. In the courfe of two years I made fo ma- ny experiments with bone-alhes mixed ni mortar compofed of lim.e fand and Uhic wa- ter, in different proportions, and of thefe with divers other ingredients, that I may venture to fay I attained a thorough knowledge of their effeas, and need not hefitate to relate them in the ftyle of precept. The forted bone-a(hes, mixed with mortar in any quantity not exceeding that of thei ^mc, difpofe the cement to fet fpeedily with- out [ 177 1 oitt cracking; and effedually fecure it from cracking, if it does not contain lime in lu- perfluous quantity : They likewife give a texture which is the more fpongy as the quantity of the bone-afhes is greater; and they accelerate the induration of it through the whole mafs. The forted bone-afhes encreafe the plafti- city of frefh mortar which is made with the fmaller quantities of lime in order to fecure the work from fiffures ; and thus they are ufeful In a triple view, in external incruftati- ons ; by facilitating the operation of plaif- tering, by preventing cracks, and by bring- ing the incruftation quickly to a ftate in which it is not eafily injured by unexpected rain. When the forted bone-afhes exceed the lime in quantity, they fenfibly injure the ce- ment, by rendering it weaker. How thefe alhes, which are not equivalent to fand in the hardnefs of their grains, nor to lime in their cementing powers, operate to weaken the cement,*may eafily be conceived, in con- N fequence [ t/s ] fequence of the obfervations made in the ninth, twelfth and thirteenth fedions. When the forted bdne-afhes are mixed in mortar in the quantity of one-fourth of the lime, they improve the plafticity, if the mortar be fhort, and they produce the defire- able efFefts above mentioned in a fenfible de- gree, without weakening the cement in the fame proportion. As a fmaller quantity of them feems to be ufelefs, and a greater quantity than that of the lime injurious, the following rules are to be obferved. When the artlft is more felicitous to fe- cure an incruftation from the effecls of hot weather, to finifh it quickly, to hide the traces of brick-work which are apt to appear thro' it, and to guard it againft rain, than to make it hard and durable in the higheft degree ; he is to ufe as much of forted bone-alhes as of lime : When the feafon, expofure, and other circumftances permit him to attend folely to the true excellence and duration of his work, he is to ufe, in our bed calcareous cement, only one part of the forted bone- afhes for every four parts of lime. By thefe rules [ ^79 ] rules he may chufe intermediate quantities adapted to his purpofes. The coarfer bone-a(hes ufed in making cupels and tefts, do not go fo far, fo the workmen exprefs themfelves, or do not ope- rate fo efFedually, as the forted alhes, in equal quantities of them by weight ; and finer or levigated bone-alhes are rather inju- rious than ufeful in the coarfer cements. The black powder of charred bones, and grey bone-aflies have nearly the fame effeds as forted bone-a(hes have, when the powder of them is forted in the fame manner ; ex- cepting what relates to colour. These obfervations on bone-afties were made before the expiration of 1777, on fpecimens of mortar laid on tiles, and fmall pieces of incruftation made on the walls of my houfe and on the fence-walls behind it : But they were not thoroughly confirmed un- til a comparifon was made between large in- crufiations laid in trying afpeds and con- taining bone-afhes, with thofe made clofe by them of my beft mortar, in the year 1778 ; N 2 when [ 'So ] when I difcovercd the difficulty expreffed in the fourteenth feclion, of making exten- five incruftations, in certain circumftances, fo free from defe£ls, as the fmaller ones were which I had made at home. In this laft mentioned year I was favoured by Mr. James Wyatt of Queen-Ann-ftreet Cavendifli-fquare, the celebrated architect of the Pantheon, and by his brother Samuel Wyatt of Berwick-ftreet, who is a very emi-^ nent builder, with the beft opportunities of making thefe comparifons : for they ordered the plaifterers employed under them to ap- ply my compofitions in a workman-like man- ner, in different afpeds and in large quantitv, and thus enabled me to judge truly of the merits of them. By the analogy of bone-afhes to cinders ^or afhes of other bodies, by the efftdis of •them in my experiments, and by the obfer- vations which I have made on capital houfes and garden walls which have been fronted or entirely fluccoed with my cement, fome in the months of October November and De- cember in the year 1778, others in the Spring, [ !8i ] Spring, the hottefl weather, and the Au- tumn of 1779; I have been led into the following opinions concerning the agency of bone-alhes in calcareous cements. The mortar which contains bone^afhes, p;ar.takes in fome degree of the compreflibi- lity and fponginefs of their grains, and is the lefs liable to crack in fetting, for the fame reafoi; that fponginefs is, in any other body, an efFe(£tual preventative of iiffures in drying ; or becaufe, any contraction of the lime pafte, in confequence of the exhalation of its wa- ter, is confined to the circuit of the fpongy grains comprefled in beating trowelling and floating the cement, and is tl^ereby prevent- ed from running longitudinally to form fif- fures. The fame texture of bone-aflies cpn- tributes to this effecl, or caufes it, upon other principles which are lefs exceptionable. There is no reafon to doubt that bone-aflies, whofe grains are^ tubulated in all poffible di- redlions, which greedily imbibe water and emit air, and which render the mortar in which they are mixed manifeflly bibulous, facilitate the entry of acidulous gas into the cement ; and that this matter entering as fail- N 3 as [ l82 ] as the water exhales, occupies the place of the water in the cement, and by preventing the contradion of it, prevents fiflures. The fpeedy induration of the cement, which im- plies a quick or copious acceffion of acidu- lous gas, according to our experience, is a proof of this agency of bone-afhes, as well as an efFedt deducible from their texture ; and from thefe premifes we may ealily con- ceive how they accelerate the fetting of cal- careous incruftations, and tend to fecure them from the injuries of variable weather. These properties of bone-afhes render them peculiarly ufeful in incruftations made within doors on principal walls; and the ad- mixture of them in half the quantity of the lime, or in a greater quantity, is the improve- ment which I pointed out in the twentieth fe£lion, whereby the damp, which disfigures the common incruirations made in the cir- cumflances there defcribed, may be obviated, without our incurring the expence of lath- work. Those who know that one-fixth part of charred bones, or about one-tenth part of well [ ] well burned bones, is phofphoric acid, may have fome doubt concerning the duration of a cement in which they are mixed in large quantity, unlefs they confider that the ftrength of the cement does not depend on them, and that it is impoffible for the phof- phoric acid to quit the lime of bone^^afhes, in order to diffolve the faturated lime of the cement. Tho* the bone-afhes fhould perifh in ^ century, which is not probable, the ce- me^t is not hkely to fail on this account, provided the quantity of them is not excels iive. Thus I furmounted the difficulties menti- oned in the fourteenth fedion, and made my beft calcareous cement applicable in all ce- mentitious and cruftaceous works external or internal, without inducing in it any difagree- able colour or other imperfedion. SECTION t ^84 ] SECTION xxir, I'he specification made in Confequence of Letters Patent^ illtiji rated with Notes, IN order to guard againft abuies, and to make fome compenflition for the expences and rifques of the artifts who publicly and boldly executed, on the great fcaie, what I had defigned ; I fecured an exclulive right in my cement, by virtue of his majefty's let- ters patent, on the eighth of January 1779 : I authorized Mr. James Wyatt the archited of Queen- Ann-ftreet Cavendlfh- Square, to ufe it in the fulleft extent, knowing that he, by his knowledge pf this fubjed and his diftinguilhed tafte in J^rchiteaure, will unite? in it all the advantages of duration and ele- gance : I likewife extended this right to Samuel Wyatt the builder in Berwick-ftreet Soho, who is well inftruaied, and proyided with the means of executing any work with this cement, in the higheft perfedtion : And I intend to referve this priviledge to them, un- til [ J til the public convenience requires that it fhould be extended to others, who are capa- ble of making the fame difpofitions for the benefit of their employers, and for preferving the reputation of my inv^ention free from the ufual exactions of monopolies and the abufes of under-jobbers. As the fpeclfication of thefe letters pa- tent comprehends the moll: ufeful pradical inftrudlions deduced from the foregoing ex- periments and obfervations, and may ferve as a concife recapitulation, I fubjoin a, trmf- cript of it. SPECIFICATION. To all to whom thefe prefents fllall come 8ic. " Now know ye that in compliance with the faid provifoe, I the faid B. H. do here-. " by declare that rpy invention of a water " cement or flucco, for building repairing and " plaftering walls, and for other purpofes, is *' defcribed in the manner following (that ib to fay) drift fand, or quarry' fand, which * This is commonly called pit-fand. confifls [ '86 ] conhfts chiefly of hard quartofe flat faced"* grahis with ftarp angles ; which is the " freeft, or may be mod eafily freed by *' wafhing, from clay, falts, and calcareous " gypfeous or other grains lefs hard and *' durable than quartz ; which contains the " fmallefl: quantity pf pyrites or heavy me- *' tallic matter jnfeparable by wafhing ; and *' which fuffers the fmalleft diminution of " its bulk ill wafhing in the following *' manner, is to be preferred before any *' other ^ And where a coarfe and a fine *' fand of this kind, and correfponding in " the fize of their grains with the coarle " and fine fands hereafter defcribed, cannot " be eafily procured, Jet fuch fand of the " foregoing quality be chofen, as may bs forted and cleanfed in the following " manner. " Let the fand be fifted in ftreamlng " clear water, through a fieve which fhall *' give paflage to all fuch grains as do not * The twelfth fe£lion treats of this. 3 The rcafons of this preference are given in the fifteenth, fixteenth, nineteenth, and twentieth fcdtions. exceed [ '87 ] exceed one fixteenth of an inch in dia- " meter ; and Let the ftream of water and " the fifting be regulated fo that all the fand *f which is much finer than the Lynn-fand commonly ufed in the London glafs-houfes, " together with clay and every other matter " fpecifically lighter than fand^m^y be wafhed* *' away with the ftream, whilft the purer and " coarfer fand, which paffes thro' the fieve, fubfides in a convenient receptacle, and ^' whilfl: the coarfe rubbifh and fliingles re- " main on the fieve, to be rejected, ^' Let the fand which thus fubfides in " the receptacle, be wafhed in clean ftream- " ing water, through a finer fieve, fo as to be further cleanfed and forted into two *' parcels ; a coarfer, which will remain In *' the fieve which is to give paffage to fuch grains of fand only as are lefs than one ** thirtieth of an inch in diameter, and which is to be faved apart under the name * The grounds of this treatment appear in the twelfth ar^i thirteenth fe£Uon. 5 I find that I have ufed this word improperly, on bad autho- thority. The reader is requefted to read rubble inftcad of fhingle throughout this fpecification. of [ :88 ] of coarfe ftnd ; and a finer, which will *' pafs through the fieve and fubfide in the *' water, and which is to be faved apart under the name of fine fand.— Let the *f coarfe and the fine fand be dried fepa- ^' ratelj, either in the fun, or on a clean iron " plate fet on a convenient furnace, in the f .' manner of a fand heat *' Let lime be chofen^ which is flone lime, " which heats the n>ofl: in flaking, and flakes *' the * The fand ought to be ftirred up continually until it is dried, and is then to be taken off; for otherwife the evaporation will be very flow, and the fand which li^s next the iron plate, by being overheated, will be difcoloured. 'The grounds of the inftruftions comprized in this para- graph, appear in the fecond, fourth, fifth and eleventh fedions. The preference given to ftone lime is founded on the prefent pradice in the burning of lime, and on the clofer texture of it, which prevents it from being fo foon injured by expofure to the air, as the more fpongy chalk lime is ; not on the po- pular notion that ftone linie has fomething in it whereby it ex- cels the beft chalk in the cementing properties. The real dif- ference between thefe will be Ihewen in the next fedtion. The gypfum contained in lime ftone remains unaltered or very little altered in the lime, after the burning; but it is not to be cxpeded that clay or martial matter Ihould be found in their native flate, in well burned lime ; for they concrete or vitrifie with a part of the calcareous earth, and conflitute the hard grains [ i89 3 *' the quickeft when duly watered ; which " is the frefhell: made and clofefl kept ; " which diflblves in diftilled vinegar with the leaft efFervefcence, and leaves the " fmalleft refidue infoluble, and in this re- " fidue the fmalleft quantity of clay gypfurri " or martial matter. " Let the lime chofen according to thefe " important rules, be put in a brafs-wired " iieve to the quantity of fourteen pounds. " Let the fieve be finer than either of the " foregoing; the finer, the better it will be: " Let the lime be flaked** by plunging it in " a butt grains or lumps, which remain undiflolved in weak acids, or kre fcperable from the flaked iime by fitting it immediately through a (ieve. • * This method of impregnating the water with lime is not the only one which may be adopted. It is however preferred before others, becaufe the water clears the fooner in con- fequence of its being warmed by the flaking lime, and the gypfeous part of the lime does not diftufe icfelf in the water fo freely in this way, as it does when the lime is flaked to line powder in the common method and is then blended with the water ; for tlie gypfeous part of the lime flakes, at firfl, into grains, rather than into fine powder, and will remain on the lieve, after the pure lime has pafled through, longenough to admit of the intended feparation ; but when the lime is otherwife flaked^ the gypfeous grains have time to Ikke to a finer powder, and palling [ ] a butt'fiUed with foft water and railing it out quickly and fuffering it to heat and fume, and by repeating this plunging and raifing alternately and agitating the lime, " until it be made to pafs through the fieve *' into the water ; and let the part of the lime which does not eaiily pafs through the fieve be rejeded : and let frefh portions of the lime be thus ufed, until as many' ounces of lime have pafled through the fieve, as there are quarts of water in the butt. " Let the water thus impregnated iland in the butt clofely covered '° until it becomes clear; " and through wooden" cocks placed at dif- " ferent heights in the butt, let the clear liquor paffing through the fieve, diffolvc in the water along with the lime. I have imagined that other advantages attended this method of preparing the linne water, but I cannot yit fpeak of them with precifion. • If the water contains no more acidulous gas than is ufually found in river or rain water, a fourth part of this quantity oi lime, or lefs, will be fufficient. *° ' Thte calcareous cruft which forms on the furface of the water ought not to be broke, for it aflifts in excluding the air and preventing the abforption of acidulous gas whereby the Urac water is fpoiled. Brafs cocks are apt to colour a part of the liquor. be [ '9' ] " be drawn off as faft"' and as low as the *' Ihne fubfides, forufe. This clear liquor I " call the cementing liquor The freer the " water is from faline matter, the better will " be the cementing liquor made with it. " Let fifty-fix pounds of the aforefaid " chofen lime be flaked, by gradually fprinkl- " ing on it, and efpecially on the unflaked " pieces, the cementing liquor, in aclofe'* clean place. Let the flaked part be im- *' mediately Lime water cannot be kept many days unimpaired, int« any veflels that are not perfeftly air-light. If the Ijquor be drawn off before it clears, it will contain whiting, which is in- jurious ; and if it be not inftantly ufed, after it is drawn limpid from the butt into open veflels, it will grow turbid again, and depolite the lime changed to whiting by the gas abforbed from the air. The calcareous matter which fubfides in the biut, refembles whiting the more nearly, as the lime has been more fparingly employed ; in the contrary circumftances, it approaches to the nature of lime; and in the intermediate ftate, it is fit for the common compolition of the plaifterers for infide ftucco. At the time of writing this fpecification I preferred this term before that of lime-water, ou grounds which I had not fufficiently examined. The vapour which arifes in the flaking of the lime con- tributes greatly to the flaking of thefe pieces which lie in its way ; and an unneceflTary wafte of the liquor is prevented, by applying it to the lime heaped in a pit or in a vcHCd which may redrain [ ] mediately'^ fifted through the laft men* tioned fine brafs-wired fieve : Let the lime " which pafles be ufed inflantly or kept in *' air-tight veflels, and let the part of the lime which does not pals through the fieve, be " rejedled'^ — This finer richer part of the " lime which paffes through the fieve, I call purified lime. " Let bone-afh be prepared'^ in the ufual " manner by grinding the \yhiteft burnt " bones, but let it be fifted to be much finer reftrain the iflue of the vapouf, and direi^l it through the mafs. If more of the liquor be ufed than is neceflary to flake the lime, it will create error in weighing the flaked powder, and will prevent a part of it from paifing freely through the fieve. The liquid is therefore to be ufed fparingly, and the lime which has efcaped its aftion is to be fprinkled apart with frelh liquor. When the aggregation of the lumps of lime is thus broken, it is impared much fooner than it is in the former ftate, becaufe the air more freely pervades it. This is flicwn in the fifth feftlon. Because it confifts of heterogeneous matter, or of ill burnt lime ; which laft will flake and pafs through the iieve, if the lime be not immediately fifted after the flaking, agreea- ble to the text. The reafon of this may be drawn from the fourth feftion- »' Th IS art is taught In the t>venty^fecond fe^ftion. than t i93 ] ** than the bone-afh commonly fold £oit making cupelsi " l^HE moft eligible naatesrlals for making ** my cement being thus prepared i Take " fifty-fix pounds of the coarfe fand and *' forty-two pounds of the fine fand; mix " them on a large plank of hard wood " placed horizontally ; then fpread the fand fo that it may ftand to the height of fix " inches with a flat fiirface on the plank ; " wet it with the cementing liquor ; and let " any fuperfluous'^ quantity of the liquor, which the fand in the condition defcribed " cannot retain, flow away off the plank. To the wetted fand add fourteen pounds of the purified lime in feveral fucceffive portions, mixing and beating them up toge- " ther in the mean time with the inftruments " generally ufed in making fine mortar : " then add fourteen pounds of the bone-afh *' in fucceffive portions, mixing and beating " all together. The quicker and the inore perfe(£lly thefe materials are mixed and " beaten together, and the fooner the ce- The grounds of this praftlce are fhewn in the twelfth fec- tlOQ* O meiit t 194 ] ** ment thus formed is ufed, the better it " will be. This I call the water cement Goarfe grained, which is to be applied in " building, pointing, piaiftering, fluceoing, " or other work, as mortar and ftucco now *' are ; with this difference chiefly, that as this cement is fhorter than mortar orcom- mon flucco and dries fooner, it ought to *' be worked expeditioufly in all cafes, and *' in ftuccoing it ought to be laid on by flid- ^' ing the trowel upwards on it ; that the materials ufed along with this cement " in building, or the ground on which it is to be laid in ftuccoing, ought to be well wetted *° with the cementing liquor, in These proportions are Intended for a cement made with- i\yes meant in this place are the dark grey or black fort. I am not yet fully faiisfied about the operation of them in this inv Jlance. quantity [ 199 ] " quantity of bone afties are to be omitted ; " and in the place thereof an equal meafure " of powdered terras is to be ufed ; and if " the fand employed be not of the coarfeft fort, more terras muft be added, fo that " the terras (hall be by weight one fixth part of the weight of the fand. When fueh a cement is required of the " fineft grain'' or in a fluid form, fo that " it may be applied with a brufli, flint pow- der, or the powder of any quartofe or hard " earthy fubftance may be ufed in the place " of fand, but in a quantity fmaller as the flint or other powder is finer ; fo that the The qualities and ufes of fuch'fine calcareous cement are fet forth in the thirteenth and twentieth feaions. They are recom- mended chiefly for the purpofc of fmoothing and finifhing the ftronger cruftaceous works, or for waftiing walls to a lively and uniform colour. For this laft intention, the mixture muft be as thin as new cream, and laid on brilkly with a brufli, ia dry weather; and a thick and durable coat is to be made by repeated wafliing, but is not to be attempted by ufing a thicker liquor; for the coat made with this laft is apt to fcale, whilft the former endures the weather much longer than any other thin calcareous covering that has been applied in this way. Fine yellow ochre is the chcapeft colouring ingredient for fuch a walh, when it is required to imitate Bath ftone, or the warm- vrtnte ftanes, O 4 *' fiii^t [ 200 ] flint powder or other fuch powder fhall not " be more than fix times the weight of the " lime, nor lefs than four times its weight. The greater the quantity of lime within thefe limits, the more will the cement be " liable to crack by quick drying, and vice verfa. " Where fuch fand as I prefer cannot be " conveniently procured, or where fand can. not be conveniently wafhed and forted, that fand which mofl: refembles the mix. ture of coarfe and fine fand above pre-. " fcribed, may be ufed as I have direaed, ** provided due attention is paid to the quan- " tity of the lime, which is to be the greater *9 as the fand is the f^ner and vicq " verfa, *' Where fand cannot be eafily pro- " cured, any durable ftoney body, or baked earth grofly powdered'" and forted nearly to »9 Further inftruftions may be gathered from the thlr- teenth feaion. If fea fand be well vyaftied in frefli water, it is as good as miy other rou?iJ fand, 5* The cement made with thefe and the proper quantiti e oj^mfi^i lime and lime-watpr, ^re inferiqr to the bed, as [ 201 ] to the fizes above prefcribed for fand, may " be uled in the place of fand, meafure for *' meafure, but not weight for weight, un- lefs fuch grofs powder be as heavy fpe- *' cifically as fand. ^' Sand may be cleanfed from every fofter lighter and lefs durable matter and from " that part of the fand which is too fine, by various methods preferable^* in certain circumftances, to that which I have de- ^' fcribed. *' Water maybe found naturally free from fixable gas felenite or clay : fuch water may, ^* without any notable inconvenience, be ufed ^* in the place of the cementing liquor; and ** water approaching this ftate will not re- " quire fo much Ume as I have ordered, to the grains of thefe powders ar« mpre perifliable and brittle than thofe of fand. They will not therefore be employed, unlefs for the fake of evafion, or for want of fand : in this latter cafe the finer powder ought to be waftied away. This and the nejft paragraph is inferted with a view to evafions, as well as to fuggeft the eafier and cheaper methods which may be adopted in certain circumftances, by artifts who wnderftand tlje principlei which I have endeavoured to teach. makg [ 202 j " make the cemejiting liquor ; and a cement- " ing liquor fuffioiently ufeful may be made " by various n^ethods of mixing lime and *V water in the defcribed proportions, or nearly fo. *' When ftone lime cannot be procured, chalk lime or fhell lime which beft re- *' fembks ftone lime, in the characters above " written of lime, may be ufed in the manner defcribed, except that fourteen pounds " and a half of chalk lime will be required 'it\ the place of fourteen pounds of ftone lime. ** The proportion of lime which I have pre- " fcribed above may be encreafed without *' inconvenience, when the cement or ftucco *' is to be applied where it is not liable to dry quickly ; and in the contrary circum- ftance this proportion may be diminifhed ; and the defeCl of lime in quantity or quality may be very advantageoufly fup- 3^ THfs relates to chalk Hme burned with a fufficiqnt quan- tity of fuel in kilns of the common conll:ru£tion. Chalk lim& prepared as I fliall fliew in the next feftion, will go as fiar as Hone llnrie, if not farther. plied [ ] plied by caufing a coiifiderable qtiantity " of the cementing liquor to foak into the " work, in fucceffive portions and at diftant intervals of time, fo that the calcareous *' matter of the cementing liquor, and the matter attracted from the open air, may ** fill and ftrengthea the work. The powder of almoft every well " dried or burnt animal fubftance may be uled inflead of bone-afh ; and feveral *' earthy powders, efpecially the micaceous *' and the metallic; and the elixated aflies " of divers vegetables whofe earth will not *' burn to lime ; and the afhes of mineral fuel, which are of the calcareous kind, but '* will not burn to lime ; will anfwer the ends " of bone-aih in fome degree 3? This pra(5lice is noticed, as the remedy which may be ufed for the defeats arifing from evafive meafures, and as thc^ method of giving fpongy incruftations containing bone-allies, the greateft degree of hardnefs, '* The ufcful fubftitutes for bone-aflies, have been treated of in the foregoing feftions : the metallic micaceous and earthy powders are not recom^mended in the text, but only enume- Jated for reafons which influenced the ftyle of this fpecification, and which lawyers will perceive. " The r 204 ] " The quantity of bone-afh defci ibed may " be leffened without injuring the cement, in " thofe circumftances efpecially which ad- " mit the quantity of lime to be lefiened, and " in thofe wherein the cement is not liable " to dry quickly. And the art of remedying " the defeds of lime may be advantageoufly *' pra£lifed to fupply the deficiency of bone- *' alh, efpecially in building and in making jirtificial ftqne w^ith this cement, " N. For infide work, the admixture of hair with this cement is ufeful. In witnefs whereof I the faid H. &c." TpE excellence of my cement depends firft, on the figure fize and purity of the fand; fecondly on the purity of the lime, obtained in the choice of lime-ftone, and in the perfe£l burning, and fecured in the pre- fervation pf it from air, in my method of flaking, and in the feparation of heterogeneous parts ; thirdly on the ufe of ftrong and pure lime water in the place of common water; fourthly on the proportion of fands lime water md lime ; fifthly, on the manner of mixing them; fixthly, on the knowledge of ingre- dients [ 205 ] clients and circumftances which are injurious orufeful; feventhly, on the ufe of bone- alhes o( determinate fize ; eighthly, on the art of fuiting fome of thefe to the feveral pur- pofes ; and finally on fo many other particu- lars, as render it very difficult to give a more eandid fpecification, in the ufual compafs, than this which I have enrolled, or to guard otherwife againft evafions, than by anticipat- ing them. I DO not think it neceffary to infift more minutely on the mechanical arts of applying the coarfer or finer calcareous cement, to pro- duce the moft agreeable effeds, becaufe they are known to fo many workmen employed under Meff. Wyatt, and are fo nearly related to thofe already known to the plaifterers, that they are not likely to be miffed or loft. SECTION [ 206 J SECTION XXIV. Expenmental Compartfons of Chalk-Lime with Stone-Lime » Advices to tide Manufacturers of Chalk- Lime ^ concerning the Aft of rendering k equals if not fuperior^ to Stone-Lime^ for the Purpofes of Builders Soap-Boilers and Sugar* Bakers. ALL the authors whom I have con-* fulted, who have treated of cementl- tious buildings and of Hme, from the time of Vitruvius, who wrote on thefe fubje£ts in tlie reign of the Roman Emperor Titus or before it, down to the prefent hour ; and all the artifts with whom I have converfed, agree in the opinion that lime prepared from the clofeft lime-flone makes a ftronger cement than that which is made of fpongy lime- jftone, and that the lime of chalk particularly, is iticapable of afting as effedually as the beft flone lime, in cementitious works or incru- ftations which are expofed to the weather. This [ 26; 1 This univerfal and iinqueftioned notion had gr^at influence with me in the courfe of my experiments, until I had difcovered not only the fallacy of it, hut the grounds which gave rife to it : both which I fhall now ex- pofe, in the plealing hope of rendering great fervices to many of my friends, and all who are proprietors of chalk-pits, or are obli- ged to ufe chalk-lime in their buildings. The experiments already mentioned af- forded me a great many opportunities of com- paring cements made with lime and fand, or with thefe and other ingredients in various proportions, and differing only in the kind of lime. In thefe comparifons I could not perceive that chalk lime, judicioufly pre- pared and ufed, was in any refpe6l inferior to the befi: ftone lime : but I did not content myfelf with thefe. I made a great number of cements, with the fole view of collating the refyeOiive merits of thefe kinds of lime, in fmall and great incruftations, in mafles made to refemble cut ftone, in all expofures and feafons of the year ; and after the ftri£t- eft comparifons of thofe which contained lime in equal quantities and were treated alike [ 2o8 ] alike in all refpe£ls, I was thoroughly Cdii- vuiced that my chalk lime was as good for any purpofe of this kind, as the beft ftone lime in this kingdom ; for I ufed the well- burned lime of Plymouth ftone, which I reckon among the moft excellent of our lime ftones. Plymouth lime-flone lofes feven fix- teenths of its weight, in the converfion to lime, and becomes as white as chalk. Chalk loofes a little more in the perfeft burning* Plymouth lime leaves a fmall gypfeous refi- due in the folution prefcribed in the tenth page, which is preferable to that direded in the fpecihcation : chalk-lime leaves none. Therefore the chalk-lime chemically or tech- nically tried, appears to be equal, if not fu- perior to ftone lime, in its cementing powers, when it is properly ufed. The prejudices entertained again ft chalk- lime may be traced to three fources. The lirft is that which is mentioned in the fourth lection. The vulgar criterion of the due pre- paration of lime confifts in the flaking : and as chalk, which has undergone a (light calci- nation [ ] hatien and thereby loft only a part of its aci^ dulous gas^ is capable of flaking, by reafon of its fponginefs ; the manufadurers of chalk lime content themfelves with the degree of calcination which renders it tradlable or ven- diblci and thus bring it into difrepute* The fecond foiirce is mentioned in the fifth fedion. Chalk lime imbibes acidulous gas, during its expofure to the air, much fafter than ftone lime, and is confe- quenfly more impaired or worfe, at the time of ufirig it ill mortar, than ftone lime kept iii the fame circumftances. As the lime may be greatly injured in this way, without flak* ing fenfibly ; and as there Was no fufpiclon or meafure of fuch injury, beyond what the flaking afforded 5 the acquired imperfeaion of chalk lime was confidered as the very na- ture of it. In the thirtieth page it appears that a pound of chalk lime, placed in the qui- efcent air of a chamber. Imbibes two ounces and a half of acidulous gas in two days, which is the (horteft time in which lime is Ufually expofed, if we count from the mo- ment of its being red hot to that of its being, mixed in mortar, during which interval it is in the ftate of abforption* t 1 The third fource I have difcovered la the ftru^lure of lime kihis. The cavity of a lime-kihi has the figure of a truncated cone inverted. When the charge, con- fining of lime ftone and fuel alternately ^ratified, has hurned for fome time, the fuel h cxhaufted at the lower narrow extremity of the cavity, the lime in this part cools, and ferves as a grate to the fuel and limeftonc above it, which continue to burn brifkly, for eighteen hours or longer, after the lime be- nfeath begins to cool. During this time the laft-mentioned part of the lime is expofed to a ilrong current of air; and the whole charge of lime ftands in the like current of air until the kiln is cooled, or the lime is with- drawn ; which in common practice is feldom or never done before the lixtieth or feventieth hour after the combuftion of the fuel com- menced. The Injury which lime ftone fuftalns, in thefe circumftances, which I have often imi- tated in my elaboratory, is not great ; becaufe this lime is much more compact than the chalk I'l me. But when we obferve that the pieces of chalk lime of the common kilns, and [ ] anil tbofe, which, after heating thetii fuf- ficientlj, 1 had left in the fire-place, expofed as they are in the ufual procefs, are always efferVefcent ; that good chalk lime^ in a w^eaker current of aifj imbibes more than three ounces of acidulous gas into each pound of it, in two days, according to the experiment of the thirtieth feyife obferv^e thaV only a fuperficial cruft of the [ ] the above-mentioned fluccoes is fufficiently hard, but that the internal parts may eafily be cut or broke : and they reprefent the ce- ment jis an ej^penfive compodtion. This pviblication, which fliews it to be made of clean forted fands, of bone-afhes, and of good lime in about half the quantity Xifed in the common method of making mor- tar, renders an anfwer to the lafl-mentioned ©bje^tion c^uite unneceflary. The fecond objection may be thus confi- ^ered. The fame attractive power, which draws acidulous gas from the air into lime, muft neceffarily prevent a;iy conliderable quantity of the gas from entering deeply in a recent incruftation, until the lime at the lurface is faturated with it, and confequently until a fuperficial layer of the cement is high- ly indurated. The fame matter, which du- ring its agceflion hardens this part, muft like-, wife tend to render it clofer in the texturq and lefs freely pervious to that which is flill neceffary for the induration of the internal portions : and thus it happens that an incru- ftation grows harder at the furface, in one week J [ 219 3 W.eek, than it does deeply in the fubftance, ip a year, although bpnerafties be ufed to lefieji the obftruaion of the furface. Sinpe therefore we know the reafon why the inte- rior parts of an incruflation cannot harden in a much longer time than is neceffary for the hardening of the exterior ; fince the mate- rials of the cement are the fame in the cen^ tral parts as well as at the fuperiices, and muft be equally affeaed by acidulous gas when it can reach to them ; fmce by our ex- perience of old cements compofed of lime and fand, we know that the induration ex- tends equally through the mafs of them, in the courfe of years ; it is manifeft that our ftueco will harden in due time through the whole fubflance of it, as much as it does in a fliorter tinae at the furface, and that the ob- jedion, founded on the internal weaknefs noticed in the firft year, is futile. To prove this by experiment, fcrape away the hardened fuperficial ftratum, as I have often done ; and taking care to brulh off all that you have loofened beneath, leave the jiew furface of the friable part of the cement pxpofed to the air for a few weeks. You will find [ 220 ] fii\d it to- harden like the firft furface, whilft the parts beneath it ftill continue brittle- You will perceive after a repetition of the like experiment in the fame place, that every part of the ftucco is capable of acquiring the hardnefs of the firft furface, in a few days, and confequently that the whole will accquire it in the longer time neceffaryfor the entrance of acidulous gas through the compad ej^terior With regard to the obje£lions grounded on our Ihort experience of this cement, I think they can have very little influence a- mongft informed men who know, from the writings of the antients, by the infpediou of old cements, and by the analyfis of them^ that mortar made of lime and fand can endure every trial of the weather in the moft expofed fituations for a thoufapd years or more. Such objealons deferve no better anfwer than ought to be given to an illiterate London bricklayer, who fhould objeft to the ufe of porphyry in building, becaufe he has no certainty of its being fo durable as the bricks t 221 ] bricks -which he had for many years ex- perienced. I AM aware of the opinion, which is pre- valent at this time, that the antients ufed Xomething which is unknown to us in their mortar, and that this long loft ingredient is the caufe of the duration and hardnefs of thofe cements which we fo much admire in fome of their ftru6lures. A notion founded on conjedure does not demand a ferious dif- cuffion. I will therefore treat it as a fubjefl of converfation rather than of argument. ViTRUvius in the fifth chapter of the fecond book of his architetore fpeaks thus of lime. ^are autem cum recipit aquam, & arenam calx, tunc conjirmat JiniSiuram, h^ec ejfe caufa vUelur, quod e principiis uti co'tera corpora, ita Cs? faxa funt temper at a : ^ qu^e plus habent aerh, funt tenera : qua aqua, lenta funt ah humore : qua terra, dura : qua ignis, fragiliora. Itaque ex his faxa,Ji antequam coquantur, contufa minute, mixtaque arena conjiciantur in Jlru5luram, nec folidefcunt, nec earn poterunt continerc : cum vero conje^i^ [ 222 ] tonjeBa in fornacem, ignis vehemenit firi)ore eorrepta^ amiferint priflin^ foliditatis virtutem^ tunc exujiis, cifque exhaujlis eorum viribus, relin^ quuntur patejttibus foraminibus, & inanibus : ergo liquor^ qui eft in ejus lapidis corpore^ & aer cufit exhauftus^ & ereptus fuerity habueritque in fe re^ Jidmm color em latcntem^ intindius in aqua prius^ quam exeat ignis, vim recipit, ^ humofe penetrans 1e in foraminum raritates confervefcit, ^ ita re- frigeratus rejicit ex calcis co?pore fervor em, Ideb autem quo ponder e fax a conftciuntur in fornacem, cum eximuntur, non pojfunt ad id refpondere, fed cum expmduntur, eadem magnitudine permanente^^ excodfo liquore circiter tertia parte ponderis im- mhiuta eje inveniuntur. Igitur cum patent fora- mina eorum, ^ raritates, arena" mixtionem in fe corripiunt, & ita cohd^refcunt, fccefcendoque cum elements coeunt, ^ efficiunt ftru5lurarum foliditatem. Tpie fame ignorance of the nature of linie is betrayed by Albert! and later writers^ iAnd lince we do not find any fcientific rules prefcribed by literary artifls, for the com- pofitfon of calcareous Cements with fueh chofen and forted materials as I have de- fcribed, or in fuch proportions of them ; and "fince it is highly improbable that the re- membrance [ ] membrance of an ufeful ingredient, or any knowledge once accquired in an art practifed in fo many countries nd by fo many different perfons in every age, fhould have been loft ; we have the moft fatifadory reafons for con- cluding that the antients had no Ikill beyond that of our modern builders, in the prepara- tion of lime or mortar. The ruins of Herculaneum, and other reliques of their works, furnifh us with a- bundance of bad mortar and defeclive in- cruftatioils, which are inliances of their ig- norance of thofe principles by which the befl: cement might be made equally cheap. The total ruin and obliteration of many of their buildings, argue to the fame end ; for well cemented works fufFer very little by dilapidation, by reafon of the difficulty and expence of pulling them to pieces and ap- plying the materials to other ftrudures. If to thefe conliderations I can add an expolition of the fortuitous circumftances which ren- dered fome of their cements uncommonly hard and durable, I hope I fhall not be fufpea- ed of ungenerous invidious motives, in faying that the aqueduds and other flrudures, which [ 224- 1 wtiich have been preferved to tis trirough fd many ages, by the flrength of their cement^ are monuments rather of the good luck, than of any extraordinary ikill, of thofe who built them* WnteN the neighbouring quarries afforded good lime ftone, free from gypfum, and iiich as required to be well burned before it could (lake freely ; when the preparation of the lime, at the pcMc expence, afforded no temptation for parfmciony in fuel; and when the vicinity of the lime flone, and the quick confumption of the lime in great m.af- five works, prevented thofe injuries which it fuflains in long tranfportation and expofure, in the flaking of great quantities of it at once, or in the keeping of mortar made with it ; the ignorance of the artifls could not produce any defers dependent on bad lime, becaufe necef- lity or chance inforced all that could have been fought by choice, in this inilance. When the vicinity afforded fand, clean quartofe fharp well fized and refembling our mixture of the coarfe and fine; chance fur- nifhed [ ] nilhed all that Ikiil could aim at, in tha choice and preparation of this article. When walls of immenfe thicknefs were conftru^ted chiefly with fmall ftones, in the way of boulder- work, the great confumption of mortar made every pradlicable faving of lime an objeft of great importance ; and as the mortar muft be made ftifF for fuch work, k was neither convenient nor neceffary to mix much lime in it, or to ufe fine fand in it, or to exclude the rubble from it : and thus, by motives of oeconomy and convenience^ rather than by any others, they were led to fhe meafures which infured to the cement of fuch ftrudures every perfe6lion dependent on the goodnefs of lime and fand and on good, if not the beft, proportions of them. When the ftones ufed in building were re- cently dug, or colleded from the beds of ri- vers, the artifts needed no precautions againft the bad effefts of dry bibulous and dufty flones or bricks ; and their works had, of neceffity, every good quality attainable by the practice, which I commend, of foaking thefe materials* When their water was good, the r ] the cement abounding in lime was not much the worfe for their ignorance of the ufe of lime water. When the flruilnre was intended to fland by its own ftrength, rather than to depend on timbers ; and was by the folidity of its bear- ings and the diameter of its ftoney fubftance, fecured from agitation ; when the thicknefs of the walls, prevented the cement from being haflily dried, and afterwards fecured it from being thoroughly wetted ; and when the enor- mous weight contributed to the approxima- tion and cohefion of the parts of the cement to each other and to the ftones ; every defed oi- cementitious buildings, of a contrary de- Icription, was obviated by the nature of the llruflure, which rendered it as perfed, in the hands of any artifts, as the moft confummate Iklli could make our modern (lender tremu- lous bibulous walls. In the concurrence of thefe circumftances, vvc find excellent cements of great antiquity, which I need not point out to literary men : but llnce they are found no where elfe, that I have difcovered ; and fince it is not probable tliat the antients had any art of this kind un- known f 227 ] kndwn to the moderns, I think I am author t-lzed to conclude that their beft cementitiou3 \vorks, inftead of beitig held forth as in- flances of their unequalled Ikill, ought rather to be confidered as fubftantial proofs of the duration of mortar or ftucco duly conrtpofed of fand and lime, beyond all others, and of the utility of thefe endeavours which I have made for preparing calcareous cements according to fcientifit principles, vi^hich eilabie us to make them in the higheft perfeaion in all places, and to accommodate them to every purpdfe of ufe or ornamenti I HAVE Audioufly avoided ftri^t cohiparifons of my cement or of the beft Roman cements, with the oil cementS; becaufe the beft of thefe is private property ; not doubting that my liberal readers will give this filence a conftruc- tiori equally favourable to the piroprietors and to me. But it is not neceffary to lay myfel£ under the fame reftraint t-efpe£l:ing the re- puted improvement of Monfieur Loriot, pub- Bftied in 1774 at Paris, in a pamphlet entitl- ed, " A treatife on a new difco\^ery in the " art of building, made by Monfieur Loriot, " mechanic and pcnfionary to the king ; iri Qji *' whicl^ [ azS ] which is announced, by order of his ma- " the method of compofing a cement *' or mortar fit for an infinity of works ag " well in building as in decoration.** The firft half of this effay ferves only to difplay the fanguine hopes and lively imagi- nation of the author, which tranfported him beyond the bounds of his knowledge in this fubjed:, and all the rules of phyfical induc- tion. In the thirty-firft page he fays that the admixture of powdered quicklime, in " any mortar made whith flaked lime, is ^' the moft effedual method of giving it *' every defirable perfection ; and that this " is the chief difcovery which he announ- " ces." In the next page he gives the fol- lowing prefcription. Take one part of brick-duft finely fift- ed, two parts of fine river fand Ikreened, " and as much old flaked lime as may bq fufficient to form mortar with water, in the ufual method, but fo wet withal as to ** ferve for the flaking of as much powdered *' quick-lime as amounts to one fourth of the " -whoh quantity of brick-dufl and fand. When [ 3 " When the materials are well mixed, ern? *' ploy the compofition quickly, as the " fmalleft delay may render the application *' of it imperfed or impoffible.'* In the 40th page he fays " Another mev " thod of making the compofition is, t^ *' make a mixture of the dry materials; " that is to fay, of the fand brick- duft and powdered quick-lime, in the prefcribed proportion ; which mixture may be put " in facks, each containing a quantity fuf- " ficient for one or two troughs of" mortar. The abovementioned old (laked hme and " water being prepared apart, the mixture " is to be made, in the manner of plaifter, *' in the inftant when it is wanted, and even " on the fcafFold, and is to be well chafed with the troweh" . To exprefs Mr. Loriot's difcovery briefly and difpaffionately, I would fay, when an ignorant artift makes mortar with whiting inftead of lime, he can mend it confidera- bly by adding lime to it: but his mortar will ftill be defedlive, in comparifon with jhe befl that may be made, by reafon of the 0^3 old *[ ] old flaked lime or whiting. For on repeat e4 trials I found this to be the true ftate of the cafe, Lime fuftains lefs injury in powdering fmall quantities of it in a covered veffel, than by flaking, in the ufual method, with common water : and powdered lime, in the mixing of it with fand and water, excites a warmth in the mafs, which greatly contri* butes to its drying or fetting quickly, Mr. Loriot not knowing how to flake lime with- out impairing its cementing virtue, and taking the fpeedy exficcation as an omen of perfe6t induration, imagined the prefcrip- tion of powdered lime to be a great improve^ mtiit, If the powdering of lime, without ex^ pofmg it much to the air, were not an ex- penfive operation, I fliould have directed this powder to be ufed inflead of water-flaked lime, for thofe parts of an kcrujlation^ which are prevented from drying in due time, by their vicinity to the damp earth or to projedions on which the rain lodges. The cement to be appUed in fuch circumfl:ances pughtj^ [ ^3^ ] pught, as I faid in the fpeclficatlon, page; 202, to contain more lime than I have pre- fcribed for other fituations; and it will bq found the better for being made with pow- dered quick-lime, becaufe it will dry the fooner, and becoming pervious to air in con* fequence of the exhalation of its water, it will more fpeedily acquire that hardnefs which fecures it from being exhaufted of the lime by the conftant mgifture or the trick-* ling rain. The public are indebted to Mr. Hartley for the experimental proofs he has given of the efficacy of his method of fecuring houfes from fire ; and to lord Mahon for thofe ju- dicious and expenfive experiments by which, he has (hewn that a calcareous incruftation anfwers the purpofes of Mr. Hartley's art. I am afraid that their good intentions will be fruftrated by the indifference of men to dif- tant or improbable evils, and their diflike to any immediate expence which affords no ex- temporary convenience or ornament. But altho' fuch motives of oeconomy fhould dif- fuade us from adopting their meafures in the full^fl extent, we ought certainly to avail ourfelves [ ] imrfelves of the ufeful knowledge which they have imparted, fo far as to prefer a fafe and durable ftucco, wherever it is appli- cable by the affiftaiice of hair, before wainf- €ot or wooden ornaments. For although no metallic or calcareous covering can fecure > > > > >> ■ > >> >:> » > >> 73 ^ > :> > ::> > ^^^^ > > > > > > > . > ^ »>>^ >>:>^> ^ :> > >» > . »» > > 3>:>> > > >>» > > :> » > ^ > ^ > » >%> > > > > > ^ > ^ ''^-^^ , ^ > ^ >>Z3» ^ > > > j> > 3*> > p> . > ^» ::> :>:>> > 1^ > > >> » -> > > >~>> >> :>3