No. 2329. HYDROTALCITE GROUP OF MINERALS— FOSHAG. 



149 



The new analysis was made upon material in the type colleetion 

 of the United States National Museum (No. 874.54, gift of Robert 

 Sticht). It was crushed and examined under the micros! ope for 

 homogeneity. The only foreign material detected was the chromite. 

 The mineral was easily soluble in hydrochloric acid with efferves- 

 cence, and left, beside a residue of chromite, a small amount of floccu- 

 lent silica. The solution was evaporated to dryness and the separated 

 silica filtered off. The iron, aluminum, and chromium were separated 

 from the magnesia by a double precipitation with ammonium hy- 

 droxide. The filtered hydroxides were fused with sodium carbonate, 

 the fusion leached with hot water, the residue dissolved, and the 

 iron precipitated twice. The aluminum was precipitated from the 

 solution after the oxidization of the chromium by evaporation of the 

 filtrate with nitric acid and potassium chlorate. The chromium was 

 reduced by evaporation with hydrochloric acid and alcohol and pre- 

 cipitated twice w ith ammonium hydroxide. The carbon dioxide was 

 determined by absorption in a potash bulb and the water by Pen- 

 field's method. 



Analyses and ratios of stichtitc. 



