iafii Keiif Method ofmalhtg Cement for Terraces ; -> 



V^itrified lava, natural and ai'tilicial puzzolana, the fcorire 

 ©f Furnaces, pounded bricks, bouc-alLes, have been the bafes 

 of all the cements hitherto made, and they have been ob- 

 tained more or lefs fotid. Cements compofed in this manner 

 have been attended with perfect fuccels in the foiuhern parts 

 of Europe, little expolcd to rain : thev do not abforb the ex- 

 terior moiiiure, and the frort has not pow er to dilate their 

 pores or to dedroy their aggregation . 



The cements oF Italy, Africa, Spain, and other warm coun- 

 tries, unite all thofe qualities which can be defired by the mod 

 exaft obferver: but in our rainy countries, expofed to very 

 ftrong frofts, cements ought to polVcfs a more effential qua- 

 lity than hardncfs or foliditv, that is to fay, impermeability. 

 Cements compofed of porous bodies cannot poHefs this qua- 

 lity : being hard, and having their grcatcft folidrty during 

 lummcr, the rains of autumn gradtially penetrate to their in- 

 terior parts, to reduce to powder that mafs which a little be- 

 fore had the appearance of the greateft hardnefs. 



The inventors of the moft celebroted cements have feen 

 their experiments fail becaufe they neglcfted this effential 

 quality. The interpofition of a fat body was long ago em- 

 ployed. Pliny and Vitruvius recommend the thick part of 

 oil, and oil ilfelf ; but thcfc bodies employed alone can never 

 anfwer the intended purpofe. Oil with the lime of cement 

 forms a faponaceous body foluble in water: the tliick part of 

 «il contains a very large quantity of mucilage, which water 

 diirolves or carries oft". 



To pieferve the Iwttoms of vefTels, and to render them im- 

 permeable to water, reiinous bodies have been employed, and 

 particularly liquid pitch. I have tliouglu that my cement 

 fhould be covered with boiling pitch, as this rcfinous body 

 penetrates its pores and renders it impermeable to water. 

 One inconvenience, however, appeared in the ufe of pitch, 

 which is, its property of becoming foft during the heat of 

 fummer. 'Ihis inconvenience I remedied by bcfprinkling 

 the pitch with powder of lime : the lime combines v/ith the 

 pitch, and forms on the cement an exterior firatuni of new 

 cement refeinbling the famous cement of the Romans called 

 maltha. 



AH the merit of my labour confifls merely in having firft 

 employed, for prcfcrvlng cements and rendering them im- 

 permeable, a fat tody capable of penetrating them, of filling 

 up their pores, and of being infoluble in water. 



I fliall hgre give the method which I em|)loy for making 

 mv cement; but I mull firft obfcrvc, that there cannot be 

 one general me'.tiod of corapofing cements, unlefs lime-ftone 



and 



