ORTHOCLASE. 1 \1 



and the lime precipitated by oxalate of ammonia. The 

 filtered solution is concentrated by evaporation, and 

 the boracic acid separated as in No. 78 as a double 

 fluoride of boron and potassium. 



For the determination of the soda another portion is 

 dissolved, the lime precipitated by oxalate of ammonia, 

 the filtrate evaporated to dryness, and heated to drive 

 oft' the ammoniacal salts. The mass is then digested 

 with strong hydrofluoric acid, evaporated to dryness, 

 digested with concentrated sulphuric acid, and evapo- 

 rated to drive off the fluoride of boron. The sulphate 

 of soda is finally ignited, a piece of carbonate of am- 

 monia being held in the crucible. 



80. ORTHOCLASE. 

 KO,Si0 2 +Al 2 3 ,3Si0 2 . 



I. The very finely-powdered and levigated mineral, 

 dried at about 200, is very intimately mixed, in a 

 capacious platinum crucible, with 4 or 5 parts of car- 

 bonate of baryta ; the crucible is then inclosed in an 

 earthen crucible, which is placed in a wind-furnace 

 with a good draught, and exposed for at least half an 

 hour to an intense white heat, so that the contents may 

 be firmly aggregated into a cinder-like mass. The 

 decomposition takes place more rapidly, and with 

 greater certainty, when the crucible is exposed to a 

 blowpipe flame, so that the mass fuses completely. 



Or the mineral is mixed, in a silver crucible, with 

 4 parts of hydrate of baryta, previously freed by heat 

 from its water of crystallization, and the mixture heated 

 to fusion. 



The mass is then turned out of the crucible into a 

 capacious dish, a quantity of water poured over it, and 

 hydrochloric acid gradually added in slight excess, 



