20 ESSAY I. 



(d) The solutions of vitriolated iron, copper, and zinc 

 of alum and vitriolated magnesia, were but little affected 

 by the fluor acid. 



SECTION XXXIII. 



From what has been said of the fluor acid hitherto, 

 it follows 



(a) That it dissolves siliceous earth (Sec. xxvi.). 



(&) That it parts from this earth as soon as it finds 

 some other substance, alkali (Sees, xxvii., xxvni., xxix.), 

 absorbent earths (Sec. xxx.), metals (Sec. xxxi.), to unite 

 with. 



(c) That the fluor produced by art (Sec. x.) was not 

 quite pure, but mixed with siliceous earth ; which, however, 

 does not militate against the assertion mentioned in that 

 Section ; for the siliceous earth is obliged to remain 

 always behind when it is decomposed, together with the 

 gypsum that is formed at the same time. 



(d} That the fluor acid will hardly ever be obtained 

 pure, but always combined with some siliceous earth, which 

 may be separated from it by volatile alkali. 



(e) That if pure fluor acid is to be combined with 

 some other substance, the surest way to effectuate this is 

 to make first a kind of sal ammoniac by uniting it with 

 volatile alkali. 



(/) A compound of fixed alkali and fluor acid is capable 

 of combining with finely divided siliceous earth, via humida 

 (Sec. xxvii.). 



