prominence to the former set of characters ; he says, (page 120,) 

 under the head "metalhc seleniurets," "These are more readily 

 known than any of the other metallic compounds of the same 

 order, by the odor they emit when heated in the exterior flame, 

 the better to distinguish which the assay must be applied to the 

 nostrils whilst hot. This odor is very strong and very disagree- 

 able, and resembles that of decayed horse-radish : the smallest 

 portion of selenium may be detected by it." 



With regard to specific gravity, it is to be observed that, be- 

 sides making it occasionally a sectional or sub-sectional distinc- 

 tion, the minerals throughout the tables are arranged, as near as 

 possible, in the order of their specific gravity. 



Second Grand Division. 



All metallic minerals which fuse, partially or wholly, in the 

 flame of the blowpipe, without developing either to the sight or 

 smell the character of volatility, are included under this head. 



In this grand division there are, as in the first, two divisions, 

 but the presence or not of metallic lustre is there the distinguish- 

 ing feature. 



The subdivisions are regulated by sp. gr. in one instance — by 

 hardness in the other — the sections necessary, by specific gravity. 



Third Grand Division. 



This grand division contains those metallic minerals which are 

 almost or altogether, infusible in the flame in the blow-pipe. It 

 embraces the greater portion of the iron ores, a numerous class 

 easily recognised, for the principal part, by being magnetic, or by 

 becoming so, after roasting on charcoal ; a property which is 

 here employed to distinguish the first from the second division of 

 this grand division. 



The subdivisions are "Lustre metallic," "Lustre not metallic." 

 The Sectional divisions are founded on hardness, and where sub- 

 sections are necessary they are regulated by specific gravity. 



Fourth Grand Division. 



Herein are arranged the metallic salts as well as other metal- 

 lic minerals which may be soluble in water, (as axide of arsenic, 



