Mineral Sulphides of Iron. 209 



of the sulphur vapor in which the pyrrhotite is melted, the 

 quantity of sulphur in the product should also be raised, and 

 the melting point with it. In accord with expectation, the 

 maximum heat absorption in melting was raised about 5° when 

 the change of state took place in an atmosphere of sulphur 

 vapor. The apparatus used was the same as that shown in fig. 6, 

 except that a second furnace below the one shown in the figure 

 was used for boiling the sulphur. At the bottom of the tube 

 were placed 100 grams of sulphur, and the temperature of the 

 lower furnace (measured outside the tube) was raised gradually 

 to a little above the boiling point of the sulphur, and only 

 after the sulphur burned freely at the top of the tube was the 

 temperature of the crucible raised through the melting inter- 

 val. The experimental data follow : 



El. A 



11740 m. v. 



1188 



11726 " 



1187 



11720 " 



1186 



The maximum heat absorption is only about 5° higher than 

 it is when the pyrrhotite melts in hydrogen sulphide. A care- 

 ful comparison with the latter on a succeeding day in the same 

 apparatus left no doubt as to the reality of rise in the temper- 

 ature and as to its order of magnitude. 



Melting temp, of pyrrhotite in H 2 S on the 

 succeeding day, with the same element 



and otherwise same conditions 11683 m. v. 1183° 



11686 m. v. 1183° 



Melting point of ferrous sulphide, FeS. — Since the melt- 

 ing temperature of pyrrhotite is raised by increasing the pres- 

 sure of sulphur vapor above it, pure ferrous sulphide must melt 

 at a temperature lower than any of the sulphur solutions. In 

 the effort to obtain this point the crucible containing the pyr- 

 rhotite was heated in a vacuum furnace. The dissolved sulphur 

 volatilized in vacuo, as expected, but there was a further loss, 

 though a slow one, which was found to be due to a dissoci- 

 ation of the ferrous sulphide into the elements, a circumstance 

 which naturally prevented the exact location of the melting 

 point. 



The apparatus employed is shown in fig. 14. A is a glazed 

 porcelain tube, closed at one end, 50 cra in length. The open 

 end is closed by the perforated brass plug D, through which 

 passes the porcelain tube B which protects the thermoelement 

 JE from the action of the fused sulphide. This plug has a side 

 tube also of brass which connects with the pump. An air- 

 tight joint between the tube and plug is made with Kotinski 

 cement, GO. It was found necessary also to close the tube B by 



