P. T. Walden — Double Chlorides and Bromides, etc. 283 



however the resemblance between this fibrous mineral and 

 chrysotile is very close. They are undistinguishable under the 

 microscope, having the same silky fibers and parallel or almost 

 parallel extinction. The greatest angle of extinction measured 

 by the writer in specimens of chrysotile from Thetford, 

 Quebec, was 1-J°, in the fibrous mineral under examination, 1°. 

 It seems to correspond most nearly in chemical composition 

 to some of the fibrous forms of monoclinic amphibole, e. g. 

 antholite or kuppferite. The analyses given of the latter 

 mineral differ but little from those made by the writer ; but 

 the last edition of Dana's System of Mineralogy drops the 

 name entirely and gives antholite only a very brief reference.* 

 Probably if it is to be referred to any species beyond the broad 

 one of " fibrous amphibole containing little or no alumina," 

 the name antholite is the most appropriate. The amount of 

 combined water, which varies however in different samples, 

 seems the only objection to such a reference. 

 School of Practical Science, Toronto. 



Aet. XXXIX. — On the DovMe Chlorides and Bromides of 

 Caesium, Rubidium, Potassium and Ammonium with 

 Ferric Iron, with a description of two Ferro-ferric doid>le 

 Bromides; by P. T. Walden. 



Previous investigation on the double ferric halides seems 

 to have been devoted exclusively to the chlorides, and the 

 metal caesium has not as yet been worked within this connec- 

 tion. 



In view of these facts it appeared desirable to prepare, as 

 far as possible, a complete series of the double halogen salts 

 of the above named metals. Only negative results were 

 obtained, however, when attempts were made to prepare double 

 iodides, so that the work was necessarily confined to the chlo- 

 rides and bromides. 



The following compounds have been previously described : 



Rb 3 FeCl . K o FeCl 6 H„0. 



(NH 4 ) o Fe(Jl 6 H o 0. 



Na 2 FeCl 5 H 2 0." 



The existence of the above potassium and ammonium salts 

 has been confirmed in the present investigation but the com- 



*Dana, System of Mineralogy, 6th ed., p. 391. In the 5th ed. Kuppferite is 

 described on p. 230, and antholite on p. 2>56. Analyses 31-33, p. 237, are of 

 antholite. 



