406 Scientific Intelligence. 



ing for those crystals which possess a simple refraction, and as the an- 

 gles of these last are not subject to the slight variations which affect the 

 results in other isomorphous groups, it appeared to me of interest to 

 verify the principle of M. H. Kopp,* upon some oxyds crystallizing in 



the regular system. 



Mineralogy presents us many compounds crystallizing in the regular 

 system to which chemistry applies the most diverse .formulas. I here 

 cue them with the notation of Berzelius. 



Specific weight. 



Magnetic iron, . . . (FeO,Fe 2 3 ) . . • 5*094 



Octahedral oligist iron (martite), (Fe 2 3 ) . . 4*76 to 4*65 

 Spinelle, . .... (MgO,Al 2 3 ) . .3-48 to 3*62 

 Gahnite, . (ZnO,Al 2 3 ) . .4-23 



Ceylanite,oftheUral,(Abich)(FeO,Al 2 3 )+2(MgQ,A] 2 3 )^ 3 . 6to 3. 8 



" ofVesuvius,(Abich)(FeO,A! 2 3 )+9(MgO,Al 2 3 ) 



)} 



u u u 



3-59 



(G. Rose) } (MgO,Fe a 3 )+6(MgO, Al a 8 



Chromic iron (crystallized), > 5(MgO,Cr 2 3 )4-(FeO,Cr 2 3 ) 



Baltimore, (Abich,) J +3(FcO,Al 2 3 ) 



do. do. (compact), \ 6(MgO,Cr 9 3 )+(FeO,Cr 2 3 ) 



Baltimore, (Abich,) J +2(MgO, AUO s )-j-(FeO, Al 2 3 ) 



do. do. St. Domingo, (Berthier,) (Cr 2 O s ,'Fc 2 3 )+(Al 2 3 ) 



43 



4-5 



it it 



it it 



it it 



it u 



J+F 



Egersund, ( H. Rose,) (6FeO, Ti0 2 )+F e 



Egersund, (Mosander,) (3FeO,Ti0 2 )+Fe 

 Arendal, (Mosander,) (FeO,Ti0 2 )-i-Fe 



Uddevalla, (Plantamour,) (2(FeO, TiO„)+5Fe 



4-745 



to 



4-78 



519 



Franklinite, (Abich,) (FeO,Mn 2 3 )+(ZnO, Fe,0 3 ) J'" 



Periclase, (Damour,) (ISMgO, Fe 2 3 ) 4 3 ™ 



Perowskite, (H. Rose,) (CaO, TiO,)" t Q « 



Braunite,t (Mn 2 O a ) 4'75 to 4-818 



It is difficult to unite formulas so complicated and so diverse as those 

 which represent these oxyds, and it often happens that the same , ml |"g 

 eral species will be expressed by very different formulas although 

 crystalline form remains exactly the same. If we search for a Te .° 



between the specific gravities of these minerals and their atomic weig 



of 



for the crystals of Agersburaj: and I()9°-4ti' (over the basal edge l.uo~w/ •-- .^ r 

 of St. Marcel, while it is 109°-28' 16" in the regular octahedron. »Mt im ^ arde( i 

 ence is not so great as that which exists between the angles of substances ^' bo j ie . 

 as isomorphous, as for example, those of the different carbonates, of the r 

 dral system. oso-roan- 



We may perhaps add to the preceding list the Hausmannite , L 1 T ? a " i ?S" renc e be- 

 ganic oxyd, which crystallizes in octahedrons with a square base. ^ne di mav here 

 tween the angles is however, much greater, (105°-25' and 117 -54 .) . ,** nor phou*- 

 inquire to what limit the angles may differ in substances considered as is c £ irD j Cj 

 See on this subject the views of Mr. Laurent, (Compt. Rend, derlrav.a 



1845, p. 97.) 



