332 FACTITIOUS FUZZALONA. 



that of M, puzzolana of Italy, and might be ufed inftead of it. M. Bagge, 



s ' a Swede, isalfo known to have comp« r ed an artificial puzzo- 



lana cement, with a black, hard, and flaley fchift ; but until 

 1787, no one ever thought that the territory of France con- 

 tained in abundance non-volcanic fubftances capable of taking 

 place of the Italian puzzolana with economy and advantage. 



M. Dod-.m dif- The difcovery which I here prefent has, like many others 



chtncc. * ^ °^ £ reat utility, been the effect of chance. 



The habit of examining the nature of (lone in its bed, which 

 enables the obferver to judge of its qualities at firft fight, fixed 



Saw great beds my attention on an immenfe quantity of calciform fragments 



ofierrigunous Q f ir0 n Qre j n beds f frQm ; j fc t ( f t lh j c knefs, 



oxides at Caftel- . ° 



naudery. following exactly the paral'elifm of the (lightly inclined de* 



f)bfefved burnt clivities, in the neighbourhood of Caftlenaudery. I per- 



fiddTlikecom-' CeIved in the ad J acent fields ma »y fubftances of the fame 

 paft lava, nature fcattered over the fur face of the earth, of violet, 



brown, and black colours, which from their appearance, had 

 a perfect refemblance to compact lava, which feemed ex- 

 traordinary in a country where there was no appearance of 

 ancient craters, or of volcanic eruptions. Thefe I foon found 

 Out had been brought to this ftate by ferving as hearths, or 

 enclofures to the fires kindled in the fields by the peafants/ 

 either for agricultural purpofes, or perfonal convenience when 

 they watch their flocks in winter; as I faw foon after many 

 fimilar arranged by hand on one another for thefe purpofes. 

 whi«h fimilarity The fimilarity of thefe fragments to volcanic products 

 made him thmk excited my deiire to form a cement from them, by treating 



them fie for / i*L 



puzzolana. them in the fame manner as puzzolana earth. J. he great 



quantity of iron which thefe oxides feemed to me to contain, 



the abundance of their filiceous particles, and the alumen 



which evidently entered into their composition, their great 



weight, and their non-effervefcence with acids, altogether 



made me prefume, that the cement formed from them would 



bind under water,, and my expectation was not deceived. 



Convinced bv Fifteen months fucceffive experiments, to difcover the 



long experiments proportion of lime which this oxide would abforb to harden 



to riVlu™ ty in water > without cracking when in the air, have convinced 



me, that my factitious puzzolona had all the good properties 



Propofed for ufe of that of Italy, without its faults. At this time I determine 



in the public e( j to p rc p fe its ufe in the public works, and demanded that 



comparative experiments mould be made between it a,nd 



