MANUAL OF NATURAL HISTORY. 621 



1, pure or "Native Sulphur/' massive, or in 

 acute octahedral crystals, H. = 1*5 — 2 5, sp. 

 gr. = 2-072, yellow, lustre resinous, brittle, 

 found in volcanic regions, also in beds of 

 gypsum; 2, as binoxide or " Sulphurous acid/' 

 gaseous, colourless, sp. gr. 2*222, destroys 

 colour, evolved from active volcanoes ; 3, as 

 hydrated teroxide or " Sulphuric acid/' liquid, 

 colourless, extremely acid, sp.gr. 1*85 — 1*86, 

 occurs in a diluted state in some volcanic 

 districts. Symb. S. 

 3. Family. — Seleniides. Minerals containing Sele- 

 nium or its compounds. Occurs native in sub- 

 metallic incrustations, grayish- or brownish- 

 black, sp. gr. = 4-3, with metals it forms 

 " Seleniurets." Compounds of this metalloid 

 when heated, give off an odour resembling 

 that of horse-radish. Synth. Se. 



4. Family. — Fluoriniides. Minerals containing 



chiefly compounds of Fluorine. Occur in com- 

 bination with metals forming " Fluorides/' 

 Symb. F. 



5. Family. — Chloriniides. Minerals containing 



principally compounds of Chlorine. Occur 

 with Hydrogen as " Hydrochloric acid/' or 

 with metals forming chlorides. Symb. CI. 



6. Family. — Brominiides. Mineral substances con- 



taining principally compounds of Bromine. 

 Occur with metals as "Bromides/' in various 

 waters, as in the Dead Sea, and in salt water. 

 Symb. Br. 



