634 



CEMENTS, LIMES, AND PLASTERS. 



deposits differ greatly in the quality of the materials obtained from 

 them. Care should therefore be exercised in selecting a spot for exploita- 

 tion, and sorting of the material dug would be advisable in order to 

 keep the product of uniformly high grade. After extraction the ma* 

 terial is screened and ground. In addition it is occasionally slightly 

 roasted, which process increases its hydraulic properties. Carelessness, 

 both in the mining and in the later preparation of the pozzuolana, 

 has brought the Italian article somewhat into disrepute among Euro- 

 pean engineers. In consequence it is losing ground with respect both 

 to pozzuolana from the Azores and to trass from Rhenish Prussia. 



Pozzuolana is also obtained at a number of localities in southeastern 

 France. These localities occur mostly in three areas : (1) in the Auvergne 

 Mountains, lying in the Departments of Puy de Dome and Cantal; 

 (2) in the Mountains du Vivarais, between Haute Loire and Ardeche; 

 and (3) in the Department of PHerault, near the Gulf of Lyons. 



TABLE 235. 

 ANALYSES OF POZZUOLANA FROM FRANCE. 



1. Auvergne Mountains, black. Thorpe, Diet. App. Chem., vol. 1, p. 475. 



2. " reddish-brown. ' 

 3 " " brick-red. 



Gravenv^re. 

 Vivarais Mountains, gray. Vicat, analyst. 



brown. ' 

 Department of 1'Herault, brown. Vicat, analyst. 



Pozzuolana has been shipped from San Miguel and Terceira in the 

 Azores, to Portugal for over a hundred years, and has been used with 

 very satisfactory results in many important buildings, harbor works, etc. 

 The Azores pozzuolana varies in color from yellowish to brownish, and 

 sometimes to grayish. It is frequently so fine-grained as not to require 

 screening or grinding before use. A reddish colored variety from the 

 same islands is termed tetin. 



A similar ash, locally called "tosca", is obtained from Teneriffe, 

 one of the Canary Islands, and shipped to Spain for use as a cementing, 

 material. 



