Dr. Clarke's Analysis of a bituminous Limestone. 1J1 



water. " Puteolanus pulvis," says Seneca,* "si aquam attigit, 

 Saxum est" — It was a property so well known to the ancients, 

 that the ashes of Puteoli were exported to very distant parts of the 

 Roman Empire, to be used in the preparation of mortar for all 

 public works, such as moles, bridges, and ramparts, situate in rivers, 

 lakes, or in bays, and upon the borders of the sea.f The exca- 

 vations carried on in search of it, caused the spacious caverns and 

 extensive subterraneous galleries, afterwards used as catacombs, in 

 the neighbourhood of Naples and of Rome ; % and the same arena- 

 ceous substance has sometimes been brought even into Great Britain , 

 to be used in the fabrication of mortar, both in ancient and in 

 modern times. It may therefore be considered as a discovery of 

 some importance, that we possess, in this country, a species of lime- 

 stone which, when used for purposes of extracting lime, and in the 

 preparation of mortar, is capable of communicating to the cement 

 all the properties of the pulvis Puteolanus. 



This species of limestone is found in North Wales, in the parish 

 oiWhiteford, in Flintshire. Some specimens of it were sent to mc 

 by my friend David Pennant, Esq. son of the celebrated naturalist 

 of the same name. Its specif 'c gravity, estimated in pump water, at a 

 temperature of 50° of Farenheit, equals 2.670. It is of a dark 

 brown colour, and, when breathed upon, it exhales an earthy 

 odour, denoting the presence of iron oxide, in combination with 

 alumine ; but its colour is owing to bitumen, rather than to iron, 

 as will appear by the following analysis, undertaken at the request 

 of Mr. Pennant, for ascertaining the chemical constituents of this 



limestone. 



* Natur. Quasi. Lib. 3. Cap. 20. See also Pliny. Hist. Nat. Lib. 35. Cap. 13. 

 -f Tho pulvis Puteolanus was also used by the ancients in constructing the streets of 

 Rome, and in ;ili the great roads of the empire. See Winkelmann, Hist, tie VArt, 

 tour. 2, p. 553. 



J Winkelmann, Obscrv. stir L'Architect. des Ancicns, &c. ubi supra. 



3 i 2 



