36 WAVELL1TE AND PHOSPHATES OF ALUMINA. 



Only a small quantity of alumina is dissolved which 

 may be precipitated by gentle digestion witl^ carbonate 

 of ammonia. 



The solution of alkaline chromate filtered from the 

 alumina is carefully mixed with excess of hydrochloric 

 acid and some alcohol, and heated until it has a pure 

 emerald-green color. The sesquioxide of chromium 

 is precipitated from the hot solution by caustic ammo- 

 nia, washed, dried, ignited, and weighed. 



19. WAVELLITE AND PHOSPHATES OF ALUMINA 

 IN GENERAL. 



A1 2 3 ,P0 5 + 12HO. 



I. The mineral, which is only slightly soluble in 

 hydrochloric acid, is finely pulverized and fused with 

 caustic potassa in a silver crucible, and then dissolved 

 in hydrochloric acid, and tartaric acid added to the 

 solution until it gives no precipitate with excess of 

 ammonia. Chloride of ammonium and sulphate of 

 magnesia are then added, and the solution well closed 

 allowed to stand for 24 hours, and the precipitated 

 phosphate of magnesia-ammonia treated as in No. 6. 

 It contains basic tartrate of magnesia, which after igni- 

 tion is re-dissolved in hydrochloric acid, heated for a 

 long time, and again precipitated by ammonia. 



II. The freshly-precipitated alumina is dissolved in 

 the smallest possible quantity of caustic soda, the solu- 

 tion diluted, heated to ebullition, and a solution of 

 silicate of soda added as long as any precipitate of 

 silicate of alumina is produced. Lastly, in order to 

 precipitate the whole of the silicic acid, a concen- 

 trated solution of sal ammoniac is added, the solution 

 again boiled and filtered. From the filtrate, the phos- 



