62 T. STEERY HUNT ON 



empirical combiniug weight, deduced from chemical analysis, with that calculated from 

 their specific gravity, water being uuity. The value got by dividing this empirical 

 weight by the specific gravity, p -r- d = v, or the so-called atomic volume, is the reci- 

 procal of the coeihcient of condensation ; and, as long since pointed out by the author, the 

 hardness and chmnical indifterence of related species are inversely as the value oft'. In 

 calculating this value, as already shown in 1885, the unit for p in metalline species is for 

 convenience made the mean quantivalent weight ; that is to say, it is the number got by 

 dividing the empirical equivalent weight by the sum of the equivalents therein repre- 

 sented ; so that for marcasite, FeS^ = 120, we divide by six and liiid j> = 20, and for 

 stibnite. Sb'S'' = o3ti, Ave divide by ten and find p =■ o-Stj. 



Order META LL ATA. 



Suborder A. Metallometallixba. 



Tribe 1. Melalloidex (Metals, Alloys, metallic Selenium and Phosphorus). 

 Tribe 2. Gaknoidae (divided into three subtribes). 



a. Thiogaleuoideae ; gen. Thionites, Thiophyllites. 



/(. Selenogalenoidese; gen. Eucairites- 



c. Tellurogalenoidese ; gen. Tellurites, Telhiropliyllites. 

 Tribe 3. Bournoiioidea! ; gen. Bournonites, Empleclites. 

 Tribe 4. Pyriloidex ; gen. Pyrites, Pyritinus. 

 Tribe 5. Smaltoideœ ; gen. Smaltites, Algodonites. 

 Tribe 6. ArsenopyrUodeœ ; gen. Arsenopy rites. 



Suborder B. Spatojietallixea. 



Tribe 7. Spalometalloidese ; (Non-metallic Sulphur, Selenium, Phospliorus). 



Tribe 8. Sphaleroideœ ; gen ■ Sphalerites. 



Tribe 9. I'rousloidex ; gen. Pyrargyrites, Tennantites. 



The Metulloidea\ including alike the native metals and those artificially got, present 

 great ditt'erences of hardness and density, as well as in the value of v and in other char- 

 acters, and must be grouped in several genera or subgenera. The Galenoidece are conve- 

 niently divided into three subtribes of sulphids, selenids and tellurids. The first or 

 Thiogalenoidea» (H^2 — 3;?- = 7 — 8) embr icing the native sulphids of silver, lead 

 and copper, together with argyrodite, metacinnaliar, stibnite and bismutite ( H ^ 2 — 3 : 

 (; = 7 — • H ) includes the typical genus, Thionites. The second or Selenogalenoideœ 

 ( H ^ 2 — 3 : y = 8 — '.•'.') ) embraces the various selenids of silver, lead, copper, merciiry, 

 etc., of which emairite mny lie taken as a type. The third or Tellurogalenoidea" includes 

 the genus TellurUes, comprising the tellurids of silver, gold, lead, mercury, bismuth and 

 nickel ( H = 2;') — 30 : v = 95 — 10-.5 ). The soft. Hexible, foliated sulphids like stern- 

 bergite, argyropyrite, friesite, covelline and molyljdenite may constitute a second genus 

 of the first subtribc, with the name of Thioiihylliti's : and t(4radymite and uagj'agite 

 may form another gentis, Tellurophyllites. 



The tribe Bournonoideœ includes the large genus Bournonites ( H ^ 2 — 35 : v = 7'5 — 8) 

 consisting of doiil)le sulphids of antimony with lead, silver and copper, of which l)0ur- 

 nonite is a familiar example. The species of this genius present instructive examples of 

 progressive series, especially those represented by SIjoS^ . wPbS ; in which n has A'alues of 

 1, 2, 3, 4, 5, G, and in a related species, of 12. The large group of double sulphids of 



