THE HISTORY OF CHEMISTRY, 



of Pliny 4 , andVitruvius f, confirms this obfer- 

 vation ; for they both direct, that when it is 

 made with pit fand, a fourth part of lime mould 

 be iifcd ; and, when with river or fea fund, a 

 third pa^ according to the bulk. From expe- 

 rience, however, we are taught, that the pro- 

 portion of the materials mufl be varied, accord- 

 ing to their quality, and to particular circum- 

 ftances. The antionts burned their lime on the, 

 fpot where they were building ; and it is cer- 

 tainly of the greatefl importance to ufe it quite 

 frefh. But, even as it is, the common mortar 

 employed at prefent hardens in a feries of years, 

 and will become a perfect (lone, unleis local ob- 

 flacles arife to the abfbrption of the aerial acid, 

 or counteract its effects. 



S ii. Qf 



+ H. N. 1. xxxvi. c. 23. 

 f Arch. 1. ii. c. 5. 



J Not many years ago it has been difcovered, that the pc- 

 trcfaftion of mortar requires a much larger proportion of fand 

 than is generally given, viz. about three to one (according to 

 the obfcrvation of Pliny) ; and that by ufing lime hot from 

 the kiln, without tempering it, the mortar binds atid confo- 

 lidatcs to the hardnvfsof ftbne. It is not a little extraordina- 

 ry, that this confirmation of antient occonomy in raafonry 

 fliould have brcn fo litcly cflabliflicd. 



Kott of the Tr an/later. 



