Mineral Sulphides of Iron. 



197 



iron corrodes and dissolves porcelain, but it should be noted 

 that they made their fusions in carbon-resistance furnaces 

 without further protection from the air. 



Our unglazed crucibles appeared quite unattacked in an 

 atmosphere of hydrogen sulphide. Analyses revealed the 

 presence of about 0'25 per cent of silica in our preparations, 

 though we believe that most of this was derived from minute 

 fragments of the crucible, which are difficult to exclude entirely 

 when the cake of sulphide is broken out of the crucible. Thus 

 No. 7 gave 0*33 per cent, No. 10, 0*26 per cent, and JSTo. 3 

 gave 0*22 per cent and 0*24 per cent of silica in duplicate deter- 

 minations. This of course includes the silica in the original 

 pyrite, which, however, was negligible, — *04 per cent. 



Relation of the specific volume to the composition. — The 

 specific gravity* of each preparation was determined and from 



Table IV. f 

 Composition, density and specific volumes of pyrrhotites. 





Total 

 Sulphur 



Cal. FeS 



Cal. 



dissolved 



S. 



Sp. gr. 

 at 25° 



Cal. dens, 

 at 4° 



Cal. 

 Sp. V. 



1 



36'72 



99-59 



•41 



4-769 



4-755 



0-2103 



2 



36-86 



99-37 



•63 



4-768 



4-755 



0-2103 



3 



37-71 



98-04 



1-96 



4-691 



4-677 



0-2138 



4 



38-45 



96-89 



3-11 



4-657 



4-643 



0-2154 



5 



38-54 



96-73 



3-27 



4-646 



4-632 



0-2159 



6 



38-64 



96-57 



3-43 



4-648 



4-634 



0-2158 



7 



38-84 



96-26 



3-74 



4-633 



4-619 



0-2165 



8 



39-09 



95-86 



4-14 



4-602 



4-589 



0-2179 



9 



39-49 



95-23 



4-77 



4-598 



4-585 



0-2181 



10 



40-30 



93*96 



6-04 



4-533 



4-520 



0-2212 



f Conditions of formation. 



1. From pyrite, melted in H 2 S, kept a little above m. p. for 1 h. in nitro- 

 gen and then cooled in nitrogen. 



2. From sulphur and iron, otherwise like 1. 



3. From pyrite, heated to equilibrium in H 2 S at 1300°, then quickly 

 cooled. 



4. From pyrite, heated in H 2 S to 900°, then cooled in nitrogen. 



5. From pyrite, melted in H 2 S and cooled rather slowly in same. 



6. From marcasite, melted in H 2 S and cooled rather slowly in the same. 



7. From pyrite, heated to 800° 6 h. in H 2 S, then cooled in nitrogen. 



8. From pyrite, heated to 700° 2% h. in H 2 S, then cooled in nitrogen. 



9. From pyrite, heated to 600° 3h. in H 2 S, then cooled in nitrogen. 



10. From pyrite, heated to 600° 15 h. in H 2 S, then quickly cooled in the 

 same. 



*Day and Allen, Publication No v 31, p. 55, Carnegie Institution of Wash- 

 ington. 



