180 On natural and artificial Pttzzolano. 



the angles of the scales formed when they are broken ex- 

 hibit sharp and shining edges. 



In the same work I proposed to substitute the blackish 

 schists which are decomposed in the air for puzzolanos. 

 Those which are in cakes are best ; but in all cases they 

 must be strongly calcined, in order to give them the re- 

 quisite properties. 



M. Lepere relates that M. Vitalis, professor of chemistry 

 and secretary to the Rouen Academy, and M. Lamassen, 

 chief engineer of the department of the Lower Seine, have 

 niade most excellent puzzolano hy the calcination of some 

 ochrey earths in the environs of Rouen : this was effected 

 by burning the earth in a common furnace with alternate 

 strata of common charcoal. Tliis puzzolano was subjected 

 to some trials on a large scale, and it was composed m the 

 following manner : 



One part and a half of yellow calcined ochrey earth. 

 One part and three-fourths of well washed siliceous 

 sand. 



One part and an eighth of sour lime. 

 Two parts of chips from calcareous stone and silcx. 

 From these and several other experiments (the propor- 

 tions of which were varied) it results, that the artificial 

 puzzolano constantly exhibited the same effects as the best 

 puzzolano of Italy. M. Lepere was an eye-witness of all 

 these comparative experiments. 



There can be no doubt, therefore, that wherever there 

 are ochrey earths, artificial puzzolano may be made with 

 great facility. 



What is called Dutch terrass is in many respects similar 

 to the artificial puzzolano in question. 



The ashes, or rather scoriae, left when coals are burnt, 

 may also be applied to the same purpose. M. Guytoii 

 caused a trial to be made at Cherbourg, and it succeeded 

 well. 



M. Gratien Lepere, having been intrusted in 1804 with 

 constructing the foundation of the new arsenal at Cher- 

 bour<T, began to turn his attention to the best method of 

 supplying the puzzolano of Italy. He knew that the Swedes- 

 had already used a very hard black slate with this view,- 

 after being twice sfffongly calcined in a lime-kiln. 



M. Lepere thought he perceived a great analogy between^ 

 the Swedish stone and the rocks of Cherbourg, particularly 

 those of port Bonaparte, which, when dug into, exhibited- 

 a bUck schistus, liard, feriugiiious, and falling ofi' in scales 



of 





