SJ4f FACTITIOUS PVZZOLANi*. 



On this oceafion the celebrated Mirabeau declared the 

 difcovery to be fo valuable, «• that if it had not yet been made, 

 public encouragement Jhould be held out to excite it." 



The Conftituent Aflembly wiihed to have numerous fimilar 



eftabli foments fet on foot in France, fo well were they con- 



The troubles of vinced of its national importance ; but the misfortunes of the 

 France retards . , ... • ^ . • , , j 



the manufacture t,mes prevented the execution of a project, which the grand 



of it. Chief of the empire may eafily realize, to the advantage of 



the country, whenever it feems good to him to do fo. 



Refearches on the amelioration of our cements, and parti- 

 cularly on the nature of the materials proper to form artificial 

 puzzolana, led me to try the calcination of various fchifts, 

 of the bitumenous, ferruginous, and argillaceous forts. 



Examination of The black flatey fchift of M. Bragge, fo common in France, 

 different, fchifts. ^ nQt forgoUen . j f js alffloft ^ fame as l{]at which ftfe 



elder M. Grathieu effaced at Cherbourg laft year ; but I have 



Contain too little C on Han tly found that thefe fchifts always contain too little 



jron^ r puzzo- gj^ j perceived that their repulfion of the water was flow 



and feeble, and that their folidification in the water was owing 



to the good quality of the lime. 



I was thus obliged to recur to my quartzofe oxides of iron, 

 from their containing a greater quantity of ferruginous prin- 

 Puzzolanas owe ciples ; and can aver with the (kilful Faujas, that the puzzo- 

 the'iroaVon- ° ' anas owe tne ' r property of hardening in water folely to the 

 toined. ferruginous particles which they contain : of this I have had 



many proofs. This truth is farther demonftrated in the pud- 

 ding-ftones, the brefcias, and generaHy in all the amygdaloides 

 with a ferruginous bafe or cement. 

 Theory of ce- The theory of our cements is but little advanced ; perhaps 

 BMttOlktkad- we take fi(npie con j c a U res for proofs relative to them. We 

 cried the regeneration of (ilex, and of the carbonate of lime; 

 we know the acid gafes which perform the principal part in 

 the affair : but in this important work we have been long ig- 

 norant of the degrees of their reciprocal affinity, their quan- 

 tity, and the mode of their refpedive combinations. Our 

 knowledge on this matter is confined to a few facts. 

 Two different Many experiments have proved to me that the puzzolana, 



S^omXm. which 1 ° onc(1 r ° rias a bod y in the water > is not fit t0 be em * 

 prowed in the open air, where it cracks and chaps in all di- 

 rections. And that which is proper for the air, and which ac- 

 quires 



