On natural and artificial Puzzolano. 1 79 



frrjm Bonn and Andcrnach. AtDordreclit, al the mouthsof 

 the Rhine and Mcuse, the operation oF pounding is effected. 



But these resources are local ; and as the mauui'acture of 

 puzzolano may become general, we proceed to describe the 

 best means of attaining it. 



It would be diiHcult to assign the period at which pounded 

 bricks and the earthy residue trom the disiilJation of aqua- 

 fortis were substituted for volcanic puzzolano. Their use, 

 however, has become general, particularly where there are 

 1)0 sea-ports in the vicinity at wliich real puzzolano can 

 be furnished : even in (he South of France thi;y prefer the 

 earthy residue of the distillation of aquafortis to the best 

 puzzolanos for coating the inside of the wine tubs, which 

 are almost all of mason work, and for the cements used by 

 individuals in hydraulic works. The earth employed in the 

 South of France for the decomposition of saltpetre, by ex- 

 tracting the aquafortis from it, is an ochrey earth very much 

 charoed with iron, and more or less reddened by the oxide 

 of this metal. When it is v-. anted for cement, it is only- 

 necessary to beat il up with lime and a proper quantity of 

 water. M. Ltpere relates some experiments made al Paris 

 by the engineers of roads and bridges, from which it ap- 

 pears that an immersion of eight days was sufficient for 

 aquafortis cements to acquire a hardness fit to resist a billet 

 ot wood when forced agauist it with the whole strength of 

 a man ; whereas the Italian puzzolano required six weeks 

 before it attained the same degree of hardness. 



In general the quality of the earth is beutr in proportion 

 as it is charoed wich iron. 



This last observstion is equally applicable to pounded 

 bricks : in general they do not make a good cement unless 

 they are well burnt, and made of verv ferruginous earth. 



Twenty years ago 1 suggested the above substitutes for 

 puzzolano; and the result of mycomparative trials made in 

 the port of Cette, under the inspection of the engineers of 

 the province of Languedoc, was published in 1787, in a 

 memoir printed by J^idot, by order of the states-general of 

 the i)rovincc. 



'J"hc means which I suggested for making this artificial 

 puzzolano are simple, and mav be put in practice almost 

 every where. Balls should be made of the ochrey earth, 

 and burned in a lime or potter's kiln. In order to form 

 these balls, the earth must be moistened with a sufficient 

 <iuauiiiy of water; and when the balls are made, they should 

 be burned until ihcy pass from a red to a black colour, and 

 M a • the 



