210 CLAY. 



process being also conducted as in that analysis, so 

 that the other bases may, if necessary, be again deter- 

 mined here. 



111. CLAY. 



3 A1 2 O 3 , 4 Si0 2 + 6 HO, with variable quantities of 

 KO, MgO, FeO ; MnO, Feldspar, Sand, &o. 



The water is determined by igniting the clay pre- 

 viously dried at 100. 



I. The clay is heated with concentrated sulphuric 

 acid, the greater excess of acid evaporated, the residue 

 dissolved in concentrated hydrochloric acid, by the aid 

 of heat, and the silicic acid filtered off. If the clay 

 contain an admixture of sand or feldspar, the silica is 

 dissolved in a boiling concentrated solution of carbo- 

 nate of soda, when the sand and feldspar remain un- 

 dissolved. 



The hydrochloric solution is considerably diluted, 

 and gradually neutralized with carbonate of soda, as 

 in No. 25, so that sesquioxide of iron and alumina are 

 precipitated, while protoxide of manganese, lime, and 

 magnesia, remain in solution as bicarbonates. The 

 separation of alumina and sesquioxide of iron is then 

 effected as in No. 21, that of the other bases as in No. 

 25. 



II. The clay is fused with three times its weight of 

 carbonate of potassa and soda (see No. 10), the fused 

 mass dissolved in dilute hydrochloric acid, the solu- 

 tion evaporated to dryness, the residue dissolved in 

 water containing hydrochloric acid, and the solution 

 filtered off'. 



The separation of the other bases contained in the 

 solution is then effected as in I. 



III. For the determination of the alkali, a separate 

 portion of the clay is decomposed by fusion with hy- 



