198 DOMAIN X. TkAKSILIENT. 



friable or spotty; and its edges then become 

 more translucent. 



" Reduced to powder, and digested in the 

 nitrous acid, it loses 45 hundredths of its weight; 

 and the residuum, of a fine white, and truly sili- 

 ceous, dissolves with effervescen-je in the mineral 

 alkali. It is cold to the touch : its specific 

 weight is 2,301. 



" lender the blow-pipe it begins to rack a 

 little, then it melts in boiling to a white scoria; 

 the fusibility of which expressed by a globule, 

 equal to 0,8, answers to 71 degrees of Wedge- 

 Wood's thermometer; but the small fragments 

 that have been digested in the nitrous acid, are 

 much more refractory, on account of their being 

 deprived of the calcareous earth, the principle 

 of their fusibility. Globules of them can only 

 be formed equal to 0,04, corresponding with the 

 1426 degree of Wedgewood. 



cc There are some small knots of flint scattered 

 in the interior of this stone; and its surface 

 is frequently covered with pretty black den- 

 drites. 



" I have already observed, that naturalists 

 have confounded the stones of this kind with 

 petrosilex, and particularly with the petrosilex 

 tequabilis 6f Wallerius. But its properties are 

 too remarkable, and too different from those of 



