ANALYSIS OF PHONOL1TE. 3? 



acid by washing the sand with water, they exposed it thus puri- 

 fied to the action of water saturated with carbonic acid gas. 

 After the expiration of thirty days, this water was subjected to 

 analysis, and was found to contain in solution, silica, carbonate 

 of potash, and also lime and magnesia ; thus proving that the 

 silicates contained in the sand were unable to withstand the con- 

 tinued action of water containing carbonic acid, although the 

 same silicates had resisted the short action of the aqua regia. 



Certain of the alkaline silicates found in nature contain in their 

 crystalline state water in chemical combination. In this class 

 are the zoolites, analcime, mesotype, sodalite, apophyllite, &c. ; 

 the felspars, properly so called, arc always anhydrous. 



These silicates differ very much in their behavior to acid 

 reagents. When mesotype, or a mineral corresponding to it in com- 

 position, is kept in the state of a fine powder in contact with cold 

 muriatic acid, it increases in bulk to a thick jelly. The mineral 

 being exposed to the action of the acid at the ordinary tempera- 

 ture, those constituents which are soluble in the acid are taken 

 up by it, whilst the greatest part of the silica remains undissolv- 

 ed. Labrador spar (calcareous felspar) behaves similarly when 

 treated with acids; but the minerals adularia and albite (potash 

 and soda felspars) are not attacked by acids under similar cir- 

 cumstances. 



The difference in properties, with respect to reagents, enables 

 us to decompose very complex kinds of rocks into their constitu- 

 ent parts. C. Gmelin used a process in the analysis of phonolite, 

 or clinkstone rock, by which we may separate and determine 

 the amount of the minerals capable of disintegration contained 

 in different kinds of rocks or soils submitted to examination. For 

 example, phonolite from Abterode in the district of Hegau was 

 found to contain* — 



2*097 of a mineral analogous to mesotype, and soluble in acid* 

 11*142 of felspar, insoluble in acids 



The constituents of both these are as follows : — 



* Posjgendorf*s Annalen, Bd. x.,p 357, .s-A.4 



