

Prof. B. Silliman, Jr., on Gibbsite and Allophane. 41 5 



This method is as follows : The mineral is dissolved in sulphuric 

 acid, and a sufficient quantity of sulphate of potash is added. 

 The whole solution (which should be not very bulky), is then 

 mingled with a large quantity of strong alcohol ( T %%) and al- 

 lowed to stand for some hours. In this way alum and sulphate 



potash 



* # • 



Then fil- 



ter, wash the precipitate out with alcohol, dissolve the residue in 

 water and precipitate the alumina by ammonia. The alcoholic 



« * t • • ■ 



filtrate, containing the S and P is next evaporated to expel the 

 alcohol, supersaturated with ammonia and precipitated by chlorid 

 of calcium. The precipitate always containing sulphate of lime, is 

 washed only for a short time ; it is then dissolved in hydrochloric 

 acid and diluted with weak alcohol Gypsum separates on stand- 

 ing and is removed by filtration, and from the filtrate, ammonia 

 separates pure phosphate of lime.* 



1*432 grammes of Gibbsite in fine powder were treated by this 

 process, with every precaution to ensure accuracy. I obtained — 



'• ■ 



Al = -9209 64-160 



* # 



Ca„P = trace trace 



m 



K > 34151 



•48778f 



Mg > -300 



Insoluble :0233 1-627 



1-432 100-238 



That no doubt should remain, or any room for error, I further 

 reanalyzed the alumiua obtained from the analysis of the first 

 portion of Gibbsite (I.) by the method of Berzeiius, which I have 

 often before used with success for the separation of phosphoric 

 acid from alumina. It is briefly this : The substance is fused 

 with 6 parts of pure carbonate of soda, and l*i parts of pure silica. 

 The phosphoric acid is thus transferred to the soda, and the alu- 

 mina remains as an insoluble silicate, on treating the fused mass 

 with successive portions of hot water. The filtrate is treated 

 with bicarbonate of ammonia and boiled for some hours to sepa- 

 rate a portion of basic silicate of alumina, which the alkaline 



* ■ 

 ■ m * 



menstruum had dissolved. The filtrate containing all the P is 

 acidulated with HC1 boiled to expel carbonic acid, and being 

 evaporated to a small bulk, ammonia and sulphate of magnesia 

 are added to the cold solution, and the ammonio-magnesian phos- 

 phate allowed to crystallize out. 



* Pogg. Ann., B. 54, 406. f By the difference. 



