298 [February, 



who gave an analysis of it in his " Uebersicht der geol. Verhiiltnisse des Herzog- 

 thums Nassau ;" but without calculating its formula. He found that it contains : 



This ratio leads to the formula : 3(3RO, 8103)+ (3 AI2O3, Si03)+6 HO. 

 JBreithaupt's Thurin2;ite is, according to an analysis of Rammelsberg, 3(3RO, 

 Si03)+ (2 FeAj Si03^)-l-9 HO.* 

 These three minerals are therefore : 



Owenite 2(3RO, Si03)4-(3R203 Si03)-l-6HO. 



Aphrosiderite 3(3RO, SiOg) 4- (3AI2 O3, 8103)4-6 HO. 



Thuringite 3(3RO, 8i03)-l-(2 Fe2 O3, SiOg)^ 9 HO. 



The following are the data of Mr. Keyser's analyses, and the methods used 

 for the determination of the different constituents : 



I. 2.0770 Grammes of the mineral gave : 



I. The finely powdered mineral was dissolved in hydrochloric acid, and silica 

 separated in the usual way, with the necessary precautions. In the filtrate the 

 oxide of iron was higher oxydized by nitric acid, and sesquioxide of iron and 

 ii lumina precipitated by ammonia ; an excess of acetic acid was added to the pre- 

 cipitate and repeatedly evaporated to dryness in a water bath. In this manner 

 the acetates of iron and alumina were decomposed, and sesquioxide of iron 

 and alumina separated from the soluble acetates by filtration. Alumina 

 and iron were separated by caustic potash. Lime precipitated from the acetates 

 by oxalate of ammonia. The filtrate containing magnesia and alkalies was 

 evaporated to dryness, and heated until the ammoniacal salts were expelled; from 

 the residue the magnesia was separated from the alkalies by oxide of mercury ; 

 The chlorides of alkalies were weighed together and afterwards separated by 

 bichloride of platinum. 



II. The mineral was dissolved in hydrochloric acid and cooled, while a 

 constant current of carbonic acid passed over it, in order to prevent the oxi- 

 dation of oxide of iron by atmospheric air ; then a sufficient quantity of ter- 

 <-hloride of gold and sodium was added, and the reduced gold filtered after 24 



* Rammelsberg Handworterbuch, etc., Supplement III. 



