34 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[February, 



son the analvMS of Ihe refined theorelical consKleratioiis, by tlie aid ot 

 icli'oiir cn-'iueei- exi.lains the gradual and prolonKi'd action of limes 

 the substances witli which they are combined in tlie mixin- of mur- 



of roasting- the clay, showed, moreover, more clearly than all reasoning 

 could do, the immeuse distance which separates simple appearances 

 from realised and coniplele discoveries. 



M Yicat has carried out his felicitous investigations in a. 1 respects 

 relating lo the nscs to whicli lime is appled in masonry ; the art of burn- 

 ing-lime, of dispelling!, in the most ellectual and economic manner, the 

 carbonic acid, one of the conslituunis of calcareous rocks, is iiKlel.ted f^or 

 imporlaut remarks lo the labors of our celebrated en-'ineers ; aficr the 

 precise directions which these labours explain, there can be no hesitation 

 as to the methods lo be adopted to foresee at once what will uliimately 

 be the qualilies of any Riven samples of lime. To understand the pro- 

 cesses which must be followed to slake limes of different sorts, we may 

 consult with much prolit the result of the experiments of IM. Vicat ; the 

 choice of the materials which unite with limes of all kinds lo form mor- 

 tars will no longer be a matter of blind routine. 



The necessity of beins concise compels us to mention merely under tins 

 head the interesting researches of JI. Vicat. _ We suppress, _f>";'l|e f.^/''^^. 

 reason 

 wh 



tar We re-ret also to he compclird to refrain from the a-rce-ible task oi 

 rendering fuU justice to the admirable experiments of M. lierihicr, one of 

 the best chemists of wiiom frauce can boast. 



Cements. 



M. Vicat has occupied himself with equal success in investigating the 

 properties of cfinin/s. , , . . , 



Architects distinguish cements from mortars by their natural appear- 

 ances. The sand contained in tmrUtr exists there in the form o, gravel 

 more or less coarse, and more or le.ss apparent. The cunipusition of ce- 

 ment appears homogencons, although it contains lime, sdex, and alumina. 



No substance has gained more celebrity among builders than that 

 known at the present day as Homnn Cement. This cement, called on- 

 ginallv anuatic cement, was made in the year ITPG by IMcsi^rs. Farker 

 and Wyatt. It was the result of subjecting to heat certain nodules of 

 limestone of an ovoid form found in great abundance at some disiance 

 from London. Koman cement, mixed rather thick, solidiufs in a few 

 minutes either in air or water. There are certain works, Ihe Thanies 

 Tunnel for iustKnc(^ which could not have been executed wiihout Ko- 

 man cement. Vm\ev other circumstances this rapid solulilicalioa is a 

 real obstacle ; and in such cases it is necessary to suustitute hydraulic 

 lime, of wliich the price is much less. , . , , r 



I'arker and Wyatt mannlactured their cement, and found a sale for 

 it throughout Europe; builders used it, but no one took notice of the 

 real cause of its singular properties. The discovery of this cause be- 

 longs incontestibly to M. Vicat. We find, in fact, that ailer I'-'ving in- 

 dicated the proportion of clay which renders lime hydraulic, the skilful 

 experimenter published in 1817 this categorical observation— 



"When we increase the proportion (of clay) to 33 or 40 per cent., we 

 obtain a lime which does not slake; but it pulverises readily, and pro- 

 duces, when wetted and mixed up, a composition which quickly sets 



under water." , . ^ ., u . 



The proportion of clay indicated is precisely that of the substance ma- 

 nnfactured by Parker and Wyatt. M. Vicat made, then, from 1S17, 

 every kind, not only of hydraulic lime, but also of Roman cement. 



The duty assigned to your Committee does not permit the citation of 

 facts purely scientific; they therefore desire to remark tliat the discovery 

 of our engineer respecting cements comes, in a great measure, under the 



description of practical applications. Here, as m the case ot hydraulic 

 limes, and as in other cases to be explained hereafter, geology, enliglit- 

 ened by iM. \icat as to the industrial value of limes coulainiug a 

 quantity of clay, has directed its attention to these useful investige 

 and the French builders, not long since dependent on England, ha> 



; a large 

 gations, 

 have dis- 

 covered a great number of places"where they can prepare Roman cement. 

 M Vicat himself has pointed out more than 400. This new branch of 

 industry is carried on with much success in many depar'.ements of France. 

 If the limits of this Report permitted, we could mention here many per- 

 sons who have deserved great credit by the discovery of quarries of Ro- 

 man cement, and, among others, a skilful engineer, whom the Chamber of 

 Deputies reckons among its members, M. Lacordaire. 



POZZOLANAS AND TaRRAS. 



The natural pozzolanas, in the hands of ancient architects, farras in the 

 hands of medi;eval architects, have played too important parts to have 

 escaped the attention of M. Vicat. Despite all Ihe difficulties of the sub- 

 ject, success, as regards practical results, has completeiely crowned the 

 patient and laborious investigations of the engineer. 



Thenaiiie ofpo::uM;ia is given to a volcanic substance found m great 

 abundance in the neighbourhood of Po/.zala, and of Rome. 



Tunas is a conglomerate, also volcanic, found on the banks of the 

 Rhine, and especially in the environs of Andcrnach. 



To render rich lime hydraulic, it is sullicient to wet it in proper propor- 

 tions witli pozzolana or tarras. What more simple or convenient mode 

 could be imagined? IJut in many localities the expense of conveyance 

 renders it impossible to use either pozzolana or larras. Many attempts 

 have been made to prepare substances which possess the same properties. 

 Chaptal thought he had resolved the problem by very much calcmaliiig 

 certain schists or ochreous clay. But even supposing the properties of 



tarras and pozzolana to be reproduced in this manner, the difficulty was 

 only shifted. The schists experimented on by Chaplal are not common 

 in France; and there is, moreover, in Ihe operation recommended, even if 

 ochreous clay be employed, a circumstance the very high temperature 

 requisite, which opposes an irremediable difficulty. 



M. Vicat resolved the questions into its elcmcu'.s. This solution is as 

 follows : — 



Artificial pozzolana superior, or at least equal to the best Italian pozzo- 

 lana may be obtained by a simple manner of using clay of the purest 

 kind. This method consists in sli^hthj calcinating tlie clay, in merely 

 driving off the water of combination, and always keeping Ihe tempera- 

 ture between OOO' and 700' centigrade (1-112° lo 1 292° Fahr). 



The mind rests with satisfaction on the solutions of problems of practical 

 art when they possess this admirable simplicity. On the other hand, one 

 is astonished lo see an operation so easy that the workmen call it a tour 

 de main, enrich a kingdom, or rather the whole world with a substance 

 eminently useful, and which appeared as if it must inevitably remain the 

 privileged property of a corner of the earth once the seat of volcanic erup- 

 tions. , 1 ,• r -.r 



We should fail of our duty if, after having cited the discoveries of M. 

 Vicat in the diliicult subject of pozzolanas, we omitted to mention that M. 

 le General Treussart, whose premature loss the whole army deplores, has 

 left a work on this subject tilled with useful observations and valuable 



remarks. 



The publications of M. Vicat have long since satisfied all the necessities 

 of art, for liie execution of works in fresh waier, in canals, rivers, and 

 streams. The sea water gave rise to grave difTiculties which no one had 

 anticipated. M. Vicat has the double merit of having pointed out the 

 evil and indicated Ihe remedy. 



According lo new and quite recent researches of M. Vicat, sea water 

 has some tendency to decompose cements of every kind. It attacks in- 

 discriminately those which contain rich limes or hydraulic limes, natural 

 or artificial pozzolanas. This tendency results from the presence in the 

 water of certain acids whicii have a great alllnily for lime. M. Vicat has 

 found the means of resisting this pr.judicial effect and removing it. He 

 is at this time preparing to point out the limes, pozzolanas, and cements 

 which, prepared according to the old methods, will resist the destructive 

 action of the sea ; and with respect to others, to shew the modifications to 

 whicli they must be subjected, to acquire the same power of resistance. 

 Jt will be appreheuJud that in so nice a question M. Vicat will be in no 

 haste to announce his discoveries. We may, however, state that the 

 public will in a short time be put in possession of them. It is just to 

 state that they already tend lo the rejection of a certain kind ol pozzo- 

 lana proposed for Ihe port of Algiers, and Ihe employment of which has 

 led to such disastrous consequences. The reserve wisely maintained by 

 M Vicat gives him the opportunity of supporting his system by deci- 

 sive experiment : the artificial pozzolanas employed with so much success 

 at Calais by M. Nehou, Engineer in Chief, are found to satisfy Jortiiitously 

 the conditions, laid down by M. Vicat in his new labours, of preservation 

 against the sea. 



Statistics of Hydraulic Limes. 

 The materials forbuildina recommended by JI. Vicat did not meet with 

 the usual fate of new things. Tue proofs of superiority were palpable, 

 and the old system at once acknowledged itself vanquished. Scarcely 

 had a few mouths elapsed after the publication of the memoir of the En- 

 <'ineer of the SouilUic bridge before the artificial hydraulic lime was 

 brought into use at Paris for quays, at the landings of the bridge of Jena, 

 for the construction of four large uOuttoirs, and for the works on the Canal 

 St. Martin. , , , . . 



Since then the artificial hydraulic lime has been less used ; for it is now 

 usually substituted for the natural lime of which the price is lower, and 

 which possesses the same qualities. But we hasten lo repeat the remark 

 that it is principally owing to M. Vicat, that constructors daily avail 

 themselves of new wealth in every part of the kingdom. _ ,, . ., 



Our engineer had too much penetration to avoid the conjecture that If, 

 according to his discovery, lime became hydraulic by the simple addiUon 

 of clay, there must be innumerable formations of argillaceous lirae-stones 

 throu>'hout the kingdom capable of allbrding hydraulic lime by roasting. 

 The idea having taken possession of M. Vicat, he has for twelve years 

 explored almost everv one of our Departements. His publications under 

 the modest title Statistics of Ilyilraulic Limes, have revealed tins invalu- 

 able wealth in numberless localities where its existence was not even sus- 

 pected. The Departements where natural hydraulic liine is found in the 

 rreatcst abundance are Lot, Lot-el-Caronne, Tarn, Dordogne, (..arel, Ar- 

 deche, Drome, Gers, Charente, IlJrault, Cher, AUier, Nievre, Vinne, 

 C5te-d'Or, Ain, Isere, Jura, Doubs, Haul Khin, &c. Of twenty-four 

 Departements already explored, there are no more than six or seven, ot 

 primitive earths, where hydraulic lime is entirely wanting. 



We proceed to relate two facts which exhibit in a striking manner wh^ 

 was the state of the knowledge of practical men respecting the wealth ot 

 our country in hydraulic limes when M. Vicat commenced histsanina- 



tions for it. , ■ j rn „ 



M'hcn he visited Marseilles, a new basin was being dug. I he con- 

 tractors were at great expense to get rid of an immense quantity of calca- 

 reous refuse. On examination M. Vicat found that this matter would 

 furnish sufficient hydraulic lime for the construction of the who.e basin. 



