270 Notice of some Recent [April 



right rhomboidal prisms 116° 5', 117°, 118°. He conceives 

 that the two forms which the substances endued with di- 

 morphism present, are connected by a law like the two roots 

 of an equation of the second degree, and that one being 

 known the other may be deduced from it. The rhomboidal 

 prism would be according to the few examples we possess, 

 tbe form corresponding to the rhombohedron. He cites in 

 favour of this idea, the cases of the fer oligiste, which cry- 

 stallizes in octahedrons, and iron, which is observed some- 

 times in the form of octahedrons, and sometimes of rhom- 

 bohedrons, but he does so cautiously, because he is not 

 certain of the exact nature of these substances in their 

 different crystalline states. He remarks, that the specific 

 gravity of arragonite is a little above that of the carbo- 

 nate of lime, being 2*9 to 2*7. The specific gravity of the 

 prismatic carbonate of iron is 3*8, while that of spathic 

 iron is 3*6. He infers, from these two examples, that 

 when the atoms are so arranged as to affect the prismatic 

 form, they are more condensed than when they unite to 

 form rhombohedrons. 



11. Franklinite, according to the analysis of Abich, con- 

 sists of 



Silica -40 



Alumina .... -73 

 Peroxide of iron . . 68*88 

 Oxide of manganese . 16*32 

 Oxide of zinc . . . 10*81 



97*14 

 12. Danaite is found in Franconia. It is a gray metallic 

 mineral, very brilliant. Sp. gr. 6*214. Possesses an 

 arsenical smell when heated. According to Hayer it con- 

 sists of 



Sulphur 17*84 



Arsenic . . . . . 41*44 



Iron 32*94 



Cobalt 6*45 



Loes 1*33 



100.00 



