38 Chemical Examination of American Minerals. 



But the specimens employed by him for analysis, were 

 picked from an aggregate of franklinite, and red oxide of zinc , 

 and might, therefore, have been contaminated with a little of 

 the latter mineral. This led Dr. Torrey to wish for a new 

 analysis of it. He sent me for that purpose, specimens of 

 granular franklinite unmixed with any otiier mineral ; and 

 likewise an imperfect octahedral crystal, free from all foreign 

 matter, requesting me to subject them to a chemical exami- 

 nation. 



The color of the mineral is iron-gray ; but that of the 

 powder brown. The lustre is metallic. 



The crystals are imperfect octahedrons, quite incapable of 

 measurement. Dr. Torrey informs me that they have been 

 found three inches in diameter.* 



They are not scratched by the knife, nor by felspar ; but 

 quartz crystal scratches ihem without difficulty. 



Specific gravity of the pure crystals 5-0G9. That of 

 pieces picked out of a mixture of franklinite and red zinc, was 

 only 4'257. The specific gravity of the specimen analyzed 

 by Berthier, was 4-87. 



It acts sensibly on the magnetic needle. But it does not 

 adhere to the magnet, even when reduced to powder. Nor 

 could I detect any polarity in the crystals. 



It was easy to discover in franklinite, the three constituents 

 found by Berthier. On attempting a rigid analysis of the 

 mineral,! tried the most promising of the six methods pointed 

 out by Berthier ; but I did not succeed by any of them, in 

 separating the manganese and zinc from each other. This 

 Induced me to have recourse to chloride of lime, which I 

 found to answer perfectly. The mineral was dissolved in 



* The primitive form is the regular octahedron. Sometimes the crystals 

 are extremely perfect and brilliant. They are often truncated on all the 

 edges; more rarely they assume the form of the rhombic dodecahedron. J.T. 



