46 GENERAL DISCUSSION OF CLAYS. 



into a weighed! crucible or dish. The precipitate is 

 washed three or four times with boiling water and itihe 

 filtrate evaporated to dryness. Five drops of sul- 

 phuric acid are added to the residue, and then the cru- 

 cible or dish is brought to a hot heat, cooled in a des- 

 icator, and the alkalies are weighed as a sulphate. 



To separate the alkalies, the sulphates are dissolved 

 in hot water, acidified with hydrochloric acid, suffi- 

 cient platinum chloride added to convert both sodium 

 and potassum salts into double chlorides; the liquid 

 is evaporated to a syrup upon a water-bath, eight 

 per cent, alchohol added, and filtered through a Gooch 

 crucible or upon a tared filter paper. The precipitate 

 is thoroughly washed with eighty per cent, alcohol, 

 dried at 100 C. and weighed; the potassium oxide is 

 calculated from the double chloride of potassium and 

 platinum. 



When magnesium was present to as much as one- 

 half of one per cent., the magnesium hydroxide was 

 precipitated with barium hydroxide solution and the 

 barium in turn removed by ammonium carbonate. 

 When the amount of magnesium was less than the 

 amount named, this portion of the ordinary process 

 was not regarded as necessary. 



Silica Two grams of clay are mixed with ten 

 grams of sodium carbonate and one-half gram of pot- 

 assium nitrate and brought to a calm fusion in a plati- 

 num crucible over the blast lamp. The melt removed 

 from the crucible is treated with an excess of hydro- 

 chloric acid and evaporated in a casserole to dryness 

 upon a water^bath, and heated in an air-bath at 110 

 C. until all the hydrochloric acid is driven off. Dilute 

 hydrochloric acid is added to the casserole now, and 

 t'he solution brought to boiling and rapidly filtered. 



