SILICON. 177 



Silica 44-391 or 1-997595 

 Alumina 50 - 2-25 



Thus the atomic weight of silica, from the ana- 

 lysis of bucholzite, comes out below 2 ; but the 

 deficiency does not amount to Ftfoth part a dif- 

 ference greatly within the limits of unavoidable 

 error in such analyses. 



3. NEPHELINE. 



This mineral, which is found on Monte Som- 

 ma, near Naples, has been long known to min- 

 eralogists. It crystallizes in six sided prisms, 

 often bevelled at their extremities ; it is hard 

 enough to scratch glass, and has a specific gra- 

 vity of 2*2741. From the late analysis of this 

 mineral by Arfwedson, its constituents appear to 

 be 



Silica . 44-11 



Alumina 33-73 



Soda . 20-46 



Water . 0-62 



98-92* 



Let us suppose that in this mineral every atom 

 of alumina is combined with an atom of silica; 

 and every atom of soda with an atom and a half 

 of silica, (this is a common mode of combination 

 of soda with acids ;) and let an atom of silica 

 weigh 2, an atom of alumina 2'25, and an 

 atom of soda 4. Let us calculate the composi- 



* Kongl. Vetenskaps Acad. Handl. 1821. p. 150. 

 VOL. I. M 



