A N:o 24) The meltiiii*- and boilingpoints of metalloidsulphides. 9 



with olisteiiing lacets, resembliiio; the faces oii graiiis ot fused 

 pyromorphite. 



Tetradyinite Bic,Tc^, Bi^S^. Tetradymite sinters and 

 fuses at about 600° to a verv viscous fluid. — Crystallized 

 material from Schubkau was strongly siiitered at 602°, tetra- 

 dymite from Dolgelly fused completely at 600°, and t. from 

 Pitkäranta sintered very pronoiiiicedly at 593°. — Accordiiig 

 to M ö n k e m e y e r 1) the pure /^igTeg, which by immerous 

 mineralogists is supposed to be oiie of the chief constitiieuts 

 of the isomorphous mixtures, which are called tetradymite, 

 has the meltingpoiut 573°. 



Molybdenite MoSz- Molybdeiiite is infusible at very 

 high temperatures. This is even clear from its behaviour 

 before the blowpipe. 



Kermesite. SögSgO. The kermesite becomes a little darker 

 011 heating but does not show any other changes before the 

 fusion, wliich takes place at 517°. Satellate material from 

 South Ham, Quebec, was nearly unchanged after a conti- 

 nued heating to 513°, a little sintered at 516° and fused at 

 517°. Bundles of line crystalneedles from Bräunsdorf, near 

 Freiberg in Saxony possessed the meltingpoiut 518°. 



The knowledge of their meltingpoints may further the 

 speculations conceniing the occurrence and formation of the 

 metalloid-sulphides etc. in nature. 



The two arsenic-minerals, realgar and auripigment fuse 

 at a comparatively low temperature and their existence is 

 limited to such parts of the earths crust, which have a tem- 

 perature lower than 310° — 320°. The general increment of 

 heat in the earths crust is 1° for every 31 or 32 m of descent. 

 Accordingly the point of fusion of the minerals in ciuestioii 

 would be reached at a depth of about 10,000 m. In all such 

 regions, where volcanic activity has manifested itself in 

 comparatively recent geological times, the increase of lieat 

 is usually two or three times more rapid, which would place 

 the lower boundary of the zone, in which the arsenicsulphides 

 can exist, to 5,000 or 3,000 m. below the surface of the earth. 



1) Zeitschr. anoii,'. Ch. 46. 41.i (190.i). 



