and the life of Liquid PifS. J 2} 



and fand were cve«y where of the fame quality. The ob- 

 ferver, therefore, nui(l: examine the nature of the compofition 

 of the lime he employs, and particularly the purity of the 

 fand and filiceoiis matters: he may then vary the doles of 

 the materials of his cement as may be neceOary. 



Everv method of making cement requires, in general, that 

 the puzzolana. pounded brick, and fcorise, be reduced to 

 fine powder and fifted. This precaution is neceffary for 

 cement which is not to be covered with a lefinous body: its 

 furfaee thereby becomes fmoother and more compaft, and it 

 is lefs liable to be penetrated bv moilhue. But this advan- 

 tage is more than compenfated by the fiifures and cracks oc- 

 calioned by the fhrinking of the cement. This flirinking 

 does not take place in cement made according to my method, 

 becaufe I emplov all the matters hard, coarfelv pounded, and 

 in fragment? of the fize of a grain of wheat, and often as large 

 as peas. Thefe fragments broken in this manner prefeut 

 a great number of angles and cavities into which the calca- 

 reous part penetrates, and thus forms a kind of conne£led 

 chain, which prevents thofe cracks and fiflures fo prejudicial 

 to cement. The lime vk.-hich I employed was made from 

 hard and while limeltone of the hill of Cazeres, in the de- 

 partment of the Upper Garonne : this lime diffolves with a 

 Ibrt of ebulHtion and a great heat, and after its folulion forms 

 a white paile without any mixture of gravelly parts : it is ful- 

 ceptible of Avallowing, as the maions here term it, a great 

 deal of fand and other bard matters, but it has lefs fnengtU 

 in the open air than meagre lime, which being made from 

 niarlv (tone contains in its compofition a great many 

 baked and vitrified aririllaceous matters, which give it great 

 ftrength when expofd to the open air and to water. This 

 lime, called in the country chtiux de Bourrct, requires little 

 fand, becaufe the calcined and vitrified earthy parts which it 

 contains form wiiii it already an intimate mixture, or a kind 

 of cement: this lime, therefore, diflblved in water, acquires 

 in a little time the hardnefs of ftone. 



The lime I enqjloyed then was perfe6ily pure, without any 

 internal mixiuie of heterogeneous parts, but which has no 

 great folidity when expofed to the open air. 



1 found that a fifth part of lime was fufHcient to give to 

 ceniQnt that connecting quality ncceilary to envelop all the 

 vitrilicd and Iniceous parts of a calcareous ftratum, and, con- 

 feqiitiitlv, to give it the grcalell folidilv. Such is the prooefs 

 I entployid to form on a root, conUruC-lcd for two hundred 

 years, the joifls of which were at a great diltance from each 

 other, a terrace of forty fquare fathoms, which ftill e.xills, 

 6 and 



