J846.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



33 



ON LIMES, MORTARS, AND CEMENTS. 



From the Report to the Chamber of Deputies nf the Commission ap- 

 pointed to consider the proprietij of i;ranting a pension for life to M. Vicat; 

 Engineer in chief, and Superintendent of Bridges and I/ighwai/s. 

 By M. Arago.* 

 {Translated from the French for this Journal.) 



Your Committee, from the time of their first sitting, have fully assented 

 to the motive which suggested the proposition on which you are called to 

 deliberate. They felt convinced that in submitting the great discoveries 

 of our countrymen to the appreciation of the three constitutional powers 

 of the kingdom, that in having recourse to all the solemnities of the law 

 in regulating the reniuuerations which inventors may have deserved, they 

 stimulate to the highest degree, and in the most beneficial manner the ztal, 

 the ardour, the perseverance of men of genius. 



We speak, solely of great discoveries. Respecting extensive works, 

 however admirable in themselves, as this character does not legi- 

 timately belong to them, it does not appear our duly to invite the atten- 

 tion of the legislative Chambers. 



These considerations mark out distinctly the course which we have to 

 take. We have to examine whether M. Vicat is to be placed among the 

 privileged men whom posterity will hold in remembrance ; whether his 

 works, when they came before the public, had the indisputable character 

 of novelty : whether they possess general interest; whether, in Doe, the 

 results arising from them ought to take their rank among the brilliant in- 

 ventions for wliich our country justly claims honour. 



This brief preamble will justify the detailed observations which you 

 are about to hear. We considered that in submitting to analysis the 

 strictest and most minute a merit, so well recognised as that of M. \''icat, 

 we should inspire a salutary distrust in those mediocrities who 

 would have their names resound in this place. If the Commission have 

 attained this end, they will, without doubt, have satisfied beforehand one 

 of the objects of the Chamber. 



Manufacture of Hydraulic Limes. 



Lime, whether in a state of purity, or, as is more usual, mixed 

 with other substances, is the material used from the remotest times to 

 bind together stones and all the constituent parts of buildings. If lime 

 be not found in any part of the globe pure, the rocks from which it may 

 be extracted — the calcareous rocks — exist almost everywhere. No mine- 

 ral is so widely distributed by nature. 



It is rare that calcareous stones are entirely pure, or exclusively com- 

 posed of lime and carbonic acid. Their substance is usually made up of 

 silex, aluminum, magnesia, oxyde of iron, manganese, &;c. Thence the 

 terms adopted by mineralogists of argillaceous, magnesian, ferruginous, or 

 inanganesian limestones. 



These limestones furnish by roasting very different limes. Builders 

 distinguish many kinds of them — rich lime — poor lime — hydraulic lime. 

 Eich lime increases greatly in bulk when slaked; its weight is then more 

 than doubled. This property would be very valuable in respect of eco- 

 nomy did not rich limes remain a long time without hardening, especially in 

 the centre of masonry, and particularly where they are kept from the action 

 of the air; rich limes, moreover, are dissolved to their last particles in 

 water frequently renewed ; this solubility of the lime in time converts ma- 

 sonry into mere heaps of stones : quay-walls, for instance, which have 

 been supposed to have been built of strong masonry, and with the greatest 

 solidity. 



Is it necessary to cite examples to shew that the rich limes will not 

 harden without the action of the air? We may point to the fact that 

 M. Treussart having had to reconstruct in 1S22, at Strashurg, the foun- 

 dations of a bastion built in 1(?CG, found there the mortar as fresh as if the 

 masons had laid it some few hours before. A similar circumstance was 

 observed at Berlin by the architects who took down one of the pillars. of 

 the tower of St. Peter, built about SO years ago. 



Are we required to shew that the constant action of water dissolves 

 rich limes in masonry ? We choose among a thousand examples the de- 

 molition of the remains of the ancient sluices of the Vilaiue. During this 

 operation, it was found that, by the dissolving of the rich lime, there re- 

 mained behind the revetement walls nothing but masses without cohesion, 

 simple heaps of loose stones. 



Poor or thin lime has all the defects of rich lime, and moreover, as its 

 name indicates, but slightly increases in bulk. The use of it is therefore, 

 as much as possible, avoided. 



* Notices of M. Vicat's Iiydiaulic lime, for resisting the action of water, will be found 

 in the tirst volume of this journal, p. 4, and in vol. VI., p. '2'1'J, 



No. 101.— Vol. IX.— Feeru.\rv, 18-16. 



Builders who desire to make their works lasting, must employ exclu- 

 sively hydraulic limes, especially for foundations resting on a damp soil. 



Hydraulic limes are those which readily harden under water. This 

 property <loes not develop itself always in the same degree. The most 

 valuable hydraulic limes begin to set the second to the fourth day after 

 immersion ; at the end of a mouth they are hard and quite insoluble ; in the 

 sixth month they assume the nature of certain limestones, a blow breaks 

 them wiih a sharp sound, and the fracture has a laminated appearance. 



The uatural limestones are not distinguished in general from each other 

 by any particular physical character of their texture, hardness, specific 

 gravity, or colour, which will enable us to predict what kind of lime they 

 will furnish. The rich, the poor, and the hydraulic limes are imperfectly 

 wliite, grey, fawn-colored, red, &c. It is in the internal composition of 

 rocks, in tlie nature and proportion of their constituent principles that 

 the chemists have sought the real causes of the power of hardening 

 under water {hydraulicite). 



It has been long proved that the most pure limestones, the statuary 

 marbles, primitive or saccharoid, the marbles of Pares and Carrara, al- 

 ways give by calcination the rich lime ; it is also well known that the pro- 

 perty of liardening under water is communicated to lime by particular 

 substances contained in the material of the calcareous rock from which 

 the lime is made. But what are these substances, and in what propor- 

 tion ought they to exist in the limestone, to produce the requisite pro- 

 perty in a sufficient degree? On this point opinions have long been 

 divided. 



Bergmann (for the greatest chemists have occupied themselves with the 

 question,) attributed the char.acteristic properties of hydraulic limes to 

 the presence in them of a small proportion of the oxyde of manganese. 



Guytou-Jiorveau adopted the idea of his illustrious friend. It was 

 evident, nevertheless, that the hypothesis did not alford a general solu- 

 tion : there are known to exist natural hydraulic limes in which there is 

 no trace of tiie oxyde of manganese. It has even been stated that this 

 oxyde does not possess the property assigned to it. A sluice constructed 

 in Swe<leu, according to the notions of Bergmann, with a mortar com- 

 posed of rich lime and manganese, was found so defective that it was 

 necessary to destroy it a very short time after it was constructed. 



The earliest investigations which we are acquaiuted with on the compo- 

 sition of hydraulic limes, date from the year 1750, that is, from the epoch 

 when Siueaton proposed for bold task of building the Eddystone 

 lighthouse. This great engineer then examined with the most scrupulous 

 care the natural hydraulic lime of Aberthaw, Glamorganshire. This lime 

 had in England a certain celebrity. Treated by acids, it left a residue 

 '• vybich appeared to be a bluish clay, weighing about j^\\\ of the total 

 weight of the stone." The reddish colour which this residue acquired 

 by roasting, induced Smeaton to think the calcareous rock of Aberthaw 

 (it was already called Has) contained iron. 



Saussure published in 1786, in the second volume of his celebrated 

 travels, some observations tending to attribute the hydraulic property of 

 the limes of St, Gingoulph, in Savoy, to the combined iufiuence of manga- 

 nese, quartz, and even clay, contained in the calcareous rocks of that 

 locality. It must be added, for the sake of accuracy, that the illustrious 

 naturalist leaves his opinions in the form of simple conjectures. 



One more citation, and we shall have gone over the whole of the re- 

 searches which preceded those of M. Vicat. 



M. Collet-Descostils, Engineer of mines, having, in 1813, discovered a 

 remarkable quantity of silicious matter in a very divided state in the lime 

 ofSenonches, attributed to the presence of silex, the hydraulic property, 

 which is so energetic, and well known in this lime. 



What was wantiug in the conjectures of Smeaton, of Saussure, of Des- 

 costils ? They wanted that which transforms simple conjecture into in- 

 contestible principles ; they wanted the precision and clearness, the never- 

 failing marks of established truths ; they wanted to be resolved and sim- 

 plified — to pass, in a word, by the impulse of a powerful hand, from the 

 vague cloudy region of reveries into the place of practical truths. 



In his first essays M. Vicat made use of synthesis ; every one who had 

 remarked how much the crystalline or uolecular condition modified the 

 physical properties of certain bodies could not attach, but a limited confi- 

 dence in the advantages to arckitecture likely to proceed from the che- 

 mical analysis of limes. The experiments of iM. Vicat were directed 

 straight to the object in view. 



The natural limes of Senonches were the type of perfection. M. Vicat 

 composed an artificial lime, superior to that of Senonches. He obtained 

 this great result by calcin,ating, in proper proportions, chalk or pure 

 lime, mixed with clay. By this experiment light succeeded to obscurity, 

 certainty to doubt ; the art of building had received the accession of an 

 admirable discovery. 



We do not suppose that this merit can be contested. We cannot be- 

 lieve that the desire, unfortunately too common, of robbing a contempo- 

 rary of honor to the profit of the dead, will influence any one to exag- 

 gerate the value of the essays, hypotheses, and conjecture, previous to the 

 labours of the engineer of the bridge of Souillac. It may be proved in- 

 contestibly that iM. Vicat is not less really the discoverer in the subject 

 of hydraulic limes than Newton was when he published the Theory of the 

 Composition of White Light, or than Franklin was when he proposed 

 lightning conductors to the civilised world. The great Smeaton essayed 

 fruitlessly to render the rich lime hydraulic by the addition of clay with- 

 out preparation ; Smeaton mistaking, after repeated trials, the necessity 



