J. B. Mackintosh — Iron Sulphates from Chili. 243 



The formula corresponds to 



91 {2Fe 2 3 , 5S0 3 , 18H 3 0} +22{FeS0 4 , H 2 0} + 5{Na 2 S0 4 , H 2 0} 



The water lost at 110° C. is 1124 out of 1663 molecules repre- 

 sented in the above formula or about 12 out of each molecule 

 of 2Fe 2 3 , 5S0 3 , 18H 2 or f of total H 2 0. Readily soluble in 

 water before and after heating to 110°. 



3. Roemerite (No. 8). — Brown, crystalline ; specific gravity 

 2 "15 ; analysis gave : 



Ratio. 



S0 3 ._ 40-19 50-24 



Fe 2 3 19-40 12-125 



FeO 9-52 13-22 



Na,0 0-14 0-220 



H 2 [30-85] 171-39 



After subtracting S0 3 corresponding to ]S"a 2 present, the 

 molecular ratio is 4 : 0-97 : 1-058 : 13-7 or nearly 4:1:1. At 

 110° C. most of the H 2 is expelled with simultaneous oxida- 

 tion of part of the ferrous iron. The net loss amounts to 11'8 

 molecules of H 2 0. leading to the formula FeO, Fe„0 3 , 4SO a , 

 13-7H 2 (12H 2 Tschermak, 15H a O Linck). Readily soluble 

 in water — after heating only partially soluble. 



4. Amarantite (No. 3). — Red, crystalline, with sp. gr. = 2-005 ; 

 associated with copiapite. Analysis : 



Ratio. 



S0 3 36-15 2-0 



Fe 2 3 . 35-69 0-987 



A1 2 3 0-21 0-009 



Na s O 0-51 0-036 



H 3 [27-44] 6-75 



Hence the formula corresponds to 



Fe 2 3 , 2S0 3 , 7H 2 



When heated to 110° C, 3*48 molecules of water are expelled 

 and the residue leaves a slight insoluble basic salt on solution 

 in water. 



5. We will now consider some minerals which have not yet 

 been described and which are of seemingly definite formula. 

 The first of these (No. 9) occurs associated with copiapite and 

 amarantite, but quite distinctly separated from them, in pul- 

 verulent orange flakes which are arranged in parallel tabular 

 layers. It shows no crystalline structure, which might be ex- 

 pected if it was a direct alteration of amarantite, and there is a 

 sharp line of demarcation between the minerals on the same 

 specimen with no appearance of a transition state. Analysis 

 gave : 



